Respiratory System
互联网
| Pathophysiologic manifestations | |
| Atelectasis | |
| Bronchiectasis | |
| Cyanosis | |
| Hypoxemia | |
| Disorders | |
| Adult respiratory distress syndrome | |
| Asbestosis | |
| Asthma | |
| Chronic bronchitis | |
| Chronic obstructive pulmonary disease | |
| Cor pulmonale | |
| Emphysema | |
| Idiopathic respiratory distress syndrome of the newborn | |
| Pneumothorax | |
| Pulmonary edema | |
| Pulmonary hypertension | |
| Respiratory failure | |
| Sudden infant death syndrome |
T he respiratory system's major function is gas exchange, in which air enters the body on inhalation (inspiration), travels throughout the respiratory passages, exchanging oxygen for carbon dioxide at the tissue level, and carbon dioxide is expelled on exhalation (expiration).
The upper airway ― composed of the nose, mouth, pharynx, and larynx ― allows airflow into the lungs. This area is responsible for warming, humidifying, and filtering the air, thereby protecting the lower airway from foreign matter.
The lower airway consists of the trachea, mainstem bronchi, secondary bronchi, bronchioles, and terminal bronchioles. These structures are anatomic dead spaces and function only as passageways for moving air into and out of the lung. Distal to each terminal bronchiole is the acinus, which consists of respiratory bronchioles, alveolar ducts, and alveolar sacs. The bronchioles and ducts function as conduits, and the alveoli are the chief units of gas exchange. These final subdivisions of the bronchial tree make up the lobules ― the functional units of the lungs. (See Structure of the lobule .)
In addition to warming, humidifying, and filtering inspired air, the lower airway protects the lungs with several defense mechanisms. Clearance mechanisms include the cough reflex and mucociliary system. The mucociliary system produces mucus, trapping foreign particles. Foreign matter is then swept to the upper airway for expectoration by specialized fingerlike projections called cilia. A breakdown in the epithelium of the lungs or the mucociliary system can cause the defense mechanisms to malfunction, and pollutants and irritants then enter and inflame the lungs. The lower airway also provides immunologic protection and initiates pulmonary injury responses .
The external component of respiration (ventilation or breathing) delivers inspired air to the lower respiratory tract and alveoli. Contraction and relaxation of the respiratory muscles moves air into and out of the lungs.
Normal expiration is passive; the inspiratory muscles cease to contract, and the elastic recoil of the lungs and the chest wall causes them to contract again. These actions raise the pressure within the lungs to above atmospheric pressure, moving air from the lungs to the atmosphere.
An adult lung contains an estimated 300 million alveoli; each alveolus is supplied by many capillaries. To reach the capillary lumen, oxygen must cross the alveolar capillary membrane.
The pulmonary alveoli promote gas exchange by diffusion ― the passage of gas molecules through respiratory membranes. In diffusion, oxygen passes to the blood, and carbon dioxide, a byproduct of cellular metabolism, passes out of the blood and is channeled away.
Circulating blood delivers oxygen to the cells of the body for metabolism and transports metabolic wastes and carbon dioxide from the tissues back to the lungs. When oxygenated arterial blood reaches tissue capillaries, the oxygen diffuses from the blood into the cells because of an oxygen tension gradient. The amount of oxygen available to cells depends on the concentration of hemoglobin (the principal carrier of oxygen) in the blood; the regional blood flow; the arterial oxygen content; and cardiac output.
|
STRUCTURE OF THE LOBULE
Each lobule contains terminal bronchioles and the acinus. The acinus consists of respiratory bronchioles and the alveolar sacs. <center></center> |
Because circulation is continuous, carbon dioxide does not normally accumulate in tissues. Carbon dioxide produced during cellular respiration diffuses from tissues to regional capillaries and is transported by the systemic venous circulation. When carbon dioxide reaches the alveolar capillaries, it diffuses into the alveoli, where the partial pressure of carbon dioxide is lower. Carbon dioxide is removed from the alveoli during exhalation.
For effective gas exchange, ventilation and perfusion at the alveolar level must match closely. (See Understanding ventilation and perfusion .) The ratio of ventilation to perfusion is called the / ratio. A / mismatch can result from ventilation-perfusion dysfunction or altered lung mechanics.
The amount of air reaching the lungs carrying oxygen depends on lung volume and capacity, compliance, and resistance to airflow. Changes in compliance can occur in either the lung or the chest wall. Destruction of the lung's elastic fibers, which occurs in adult respiratory distress syndrome, decreases lung compliance. The lungs become stiff, making breathing difficult. The alveolar capillary membrane may also be affected, causing hypoxia. Chest wall compliance is affected by disorders causing thoracic deformity, muscle spasm, and abdominal distention.
Respiration is also controlled neurologically by the lateral medulla oblongata of the brain stem. Impulses travel down the phrenic nerves to the diaphragm and then down the intercostal nerves to the intercostal muscles between the ribs. The rate and depth of respiration are controlled similarly.
Apneustic and pneumotaxic centers in the pons of the midbrain influence the pattern of breathing. Stimulation of the lower pontine apneustic center (by trauma, tumor, or cerebrovascular accident) produces forceful inspiratory gasps alternating with weak expiration. This pattern does not occur if the vagi are intact. The apneustic center continually excites the medullary inspiratory center and thus facilitates inspiration. Signals from the pneumotaxic center and afferent impulses from the vagus nerve inhibit the apneustic center and “turn off” inspiration.
|
UNDERSTANDING VENTILATION AND PERFUSION
Effective gas exchange depends on the relationship between ventilation and perfusion, expressed as the / ratio. The diagrams below show what happens when the / ratio is normal and abnormal.
|
In addition, chemoreceptors respond to the hydrogen ion concentration of arterial blood (pH), the partial pressure of arterial carbon dioxide (Pa CO 2 ), and the partial pressure of arterial oxygen (Pa O 2 ). Central chemoreceptors respond indirectly to arterial blood by sensing changes in the pH of the cerebrospinal fluid (CSF). Pa CO 2 also helps regulate ventilation by impacting the pH of CSF. If Pa CO 2 is high, the respiratory rate increases; if Pa CO 2 is low, the respiratory rate decreases. Information from peripheral chemoreceptors in the carotid and aortic bodies also responds to decreased Pa O 2 and decreased pH. Either of these changes results in increased respiratory drive within minutes.
PATHOPHYSIOLOGIC MANIFESTATIONS
Pathophysiologic manifestations of respiratory disease may stem from atelectasis, bronchiectasis, cyanosis, and hypoxemia.
Atelectasis
Atelectasis occurs when the alveolar sacs or entire lung segments expand incompletely, producing a partial or complete lung collapse. This phenomenon removes certain regions of the lung from gas exchange, allowing unoxygenated blood to pass unchanged through these regions and resulting in hypoxia. Atelectasis may be chronic or acute, and often occurs in patients undergoing upper abdominal or thoracic surgery. There are two major causes of collapse due to atelectasis: absorptional atelectasis, secondary to bronchial or bronchiolar obstruction, and compression atelectasis.
Absorption atelectasis
Bronchial occlusion, which prevents air from entering the alveoli distal to the obstruction, can cause absorption atelectasis ― the air present in the alveoli is absorbed gradually into the bloodstream, and eventually the alveoli collapse. This may result from intrinsic or extrinsic bronchial obstruction. The most frequent intrinsic cause is retained secretions or exudate forming mucous plugs. Disorders such as cystic fibrosis, chronic bronchitis, or pneumonia increase the risk of absorption atelectasis. Extrinsic bronchial atelectasis usually results from occlusion caused by foreign bodies, bronchogenic carcinoma, and scar tissue.
Impaired production of surfactant can also cause absorption atelectasis. Increasing surface tension of the alveolus due to reduced surfactant leads to collapse.
Compression atelectasis
Compression atelectasis results from external compression, which drives the air out and causes the lung to collapse. This may result from upper abdominal surgical incisions, rib fractures, pleuritic chest pain, tight chest dressings, and obesity (which elevates the diaphragm and reduces tidal volume). These situations inhibit full lung expansion or make deep breathing painful, thus resulting in this disorder.
Bronchiectasis
Bronchiectasis is marked by chronic abnormal dilation of the bronchi and destruction of the bronchial walls, and can occur throughout the tracheobronchial tree. It may also be confined to a single segment or lobe. This disorder is usually bilateral in nature and involves the basilar segments of the lower lobes.
There are three forms of bronchiectasis: cylindrical, fusiform (varicose), and saccular (cystic). (See Forms of bronchiectasis .) It results from conditions associated with repeated damage to bronchial walls with abnormal mucociliary clearance, which causes a breakdown of supporting tissue adjacent to the airways. (See Causes of bronchiectasis .)
In patients with bronchiectasis, sputum stagnates in the dilated bronchi and leads to secondary infection, characterized by inflammation and leukocytic accumulations. Additional debris collects within and occludes the bronchi. Increasing pressure from the retained secretions induces mucosal injury.
Cyanosis
Cyanosis is a bluish discoloration of the skin and mucous membranes. In most populations, it is readily detectable by a visible blue tinge on the nail beds and the lips. Central cyanosis indicates a decreased oxygen saturation of the hemoglobin in arterial blood, which is best observed in the buccal mucous membranes and the lips. Peripheral cyanosis is a slowed blood circulation of the fingers and toes that is best visualized by examining the nail bed area.
| CULTURAL DIVERSITY In patients with black or dark complexions, cyanosis may not be evident in the lip area or the nail beds. A better indicator in these individuals is to assess the membranes of the oral mucosa (buccal mucous membranes) and of the conjunctivae of the eyes. |
Cyanosis is caused by desaturation with oxygen or reduced hemoglobin amounts. It develops when 5 g of hemoglobin is desaturated, even if hemoglobin counts are adequate or reduced. Conditions that result in cyanosis include decreased arterial oxygenation (indicated by low Pa O 2 ), pulmonary or cardiac right-to-left shunts, decreased cardiac output, anxiety, and a cold environment.
An individual who is not cyanotic does not necessarily have adequate oxygenation. Inadequate oxygenation of the tissues occurs in severe anemia, resulting in inadequate hemoglobin concentration. It also occurs in carbon monoxide poisoning, in which hemoglobin binds to carbon monoxide instead of to oxygen. Although assessment of these patients does not reveal cyanosis, oxygenation is inadequate.
|
FORMS OF BRONCHIECTASIS
The three types of bronchiectasis are cylindrical, fusiform (or varicose), and saccular. In cylindrical bronchiectasis, bronchioles are usually symmetrically dilated, whereas in fusiform bronchiectasis, bronchioles are deformed. In saccular bronchiectasis, large bronchi become enlarged and balloonlike. <center></center> |
Others may appear cyanotic even though oxygenation is adequate ― as in polycythemia, an abnormal increase in red blood cell count. Because the hemoglobin count is increased and oxygenation occurs at a normal rate, the patient may still present with cyanosis.
Cyanosis as a presenting condition must be interpreted in relation to the patient's underlying pathophysiology. Diagnosis of inadequate oxygenation may be confirmed by analyzing arterial blood gases and obtaining Pa O 2 measurements.
|
CAUSES OF BRONCHIECTASIS
Bronchiectasis results from conditions associated with repeated damage to bronchial walls and with abnormal mucociliary clearance, leading to a breakdown in the supporting tissue adjacent to the airways. Such conditions include:
|
Hypoxemia
Hypoxemia is reduced oxygenation of the arterial blood, evidenced by reduced Pa O 2 of arterial blood gases. It is caused by respiratory alterations, whereas hypoxia is a diminished oxygenation of tissues at the cellular level that may be caused by conditions affecting other body systems that are unrelated to alterations of pulmonary functioning. Low cardiac output or cyanide poisoning can result in hypoxia, in addition to alterations of respiration. Hypoxia can occur anywhere in the body. If hypoxia occurs in the blood, it is termed hypoxemia. Hypoxemia can lead to tissue hypoxia.
Hypoxemia can be caused by decreased oxygen content (P O 2 ) of inspired gas, hypoventilation, diffusion abnormalities, abnormal / ratios, and pulmonary right-to-left shunts. The physiologic mechanism for each cause of hypoxemia is variable. (See Major causes of hypoxemia .)
DISORDERS
Respiratory disorders can be acute or chronic. The following disorders include examples from each.
Adult respiratory distress syndrome
Adult respiratory distress syndrome (ARDS) is a form of pulmonary edema that can quickly lead to acute respiratory failure. Also known as shock lung, stiff lung, white lung, wet lung, or Da Nang lung, ARDS may follow direct or indirect injury to the lung. However, its diagnosis is difficult, and death can occur within 48 hours of onset if not promptly diagnosed and treated. A differential diagnosis needs to rule out cardiogenic pulmonary edema, pulmonary vasculitis, and diffuse pulmonary hemorrhage.
Causes
Common causes of ARDS include:
- injury to the lung from trauma (most common cause) such as airway contusion
- trauma-related factors, such as fat emboli, sepsis, shock, pulmonary contusions, and multiple transfusions, which increase the likelihood that microemboli will develop
- anaphylaxis
- aspiration of gastric contents
- diffuse pneumonia, especially viral pneumonia
- drug overdose, such as heroin, aspirin, or ethchlorvynol
- idiosyncratic drug reaction to ampicillin or hydrochlorothiazide
- inhalation of noxious gases, such as nitrous oxide, ammonia, or chlorine
- near drowning
- oxygen toxicity
- sepsis
- coronary artery bypass grafting
- hemodialysis
- leukemia
- acute miliary tuberculosis
- pancreatitis
- thrombotic thrombocytopenic purpura
- uremia
- venous air embolism.
|
MAJOR CAUSES OF HYPOXEMIA
The chart below lists the major causes of hypoxemia and contributing factors.
|
Pathophysiology
Injury in ARDS involves both the alveolar epithelium and the pulmonary capillary epithelium. A cascade of cellular and biochemical changes is triggered by the specific causative agent. Once initiated, this injury triggers neutrophils, macrophages, monocytes, and lymphocytes to produce various cytokines. The cytokines promote cellular activation, chemotaxis, and adhesion. The activated cells produce inflammatory mediators, including oxidants, proteases, kinins, growth factors, and neuropeptides, which initiate the complement cascade, intravascular coagulation, and fibrinolysis.
These cellular triggers result in increased vascular permeability to proteins, affecting the hydrostatic pressure gradient of the capillary. Elevated capillary pressure, such as results from insults of fluid overload or cardiac dysfunction in sepsis, greatly increases interstitial and alveolar edema, which is evident in dependent lung areas and can be visualized as whitened areas on chest X-rays. Alveolar closing pressure then exceeds pulmonary pressures, and alveolar closure and collapse begin.
In ARDS, fluid accumulation in the lung interstitium, the alveolar spaces, and the small airways causes the lungs to stiffen, thus impairing ventilation and reducing oxygenation of the pulmonary capillary blood. The resulting injury reduces normal blood flow to the lungs. Damage can occur directly ― by aspiration of gastric contents and inhalation of noxious gases ― or indirectly ― from chemical mediators released in response to systemic disease.
Platelets begin to aggregate and release substances, such as serotonin, bradykinin, and histamine, which attract and activate neutrophils. These substances inflame and damage the alveolar membrane and later increase capillary permeability. In the early stages of ARDS, signs and symptoms may be undetectable.
Additional chemotactic factors released include endotoxins (such as those present in septic states), tumor necrosis factor, and interleukin-1 (IL-1). The activated neutrophils release several inflammatory mediators and platelet aggravating factors that damage the alveolar capillary membrane and increase capillary permeability.
Histamines and other inflammatory substances increase capillary permeability, allowing fluids to move into the interstitial space. Consequently, the patient experiences tachypnea, dyspnea, and tachycardia. As capillary permeability increases, proteins, blood cells, and more fluid leak out, increasing interstitial osmotic pressure and causing pulmonary edema. Tachycardia, dyspnea, and cyanosis may occur. Hypoxia (usually unresponsive to increasing fraction of inspired oxygen [Fi O 2 ]), decreased pulmonary compliance, crackles, and rhonchi develop. The resulting pulmonary edema and hemorrhage significantly reduce lung compliance and impair alveolar ventilation.
The fluid in the alveoli and decreased blood flow damage surfactant in the alveoli. This reduces the ability of alveolar cells to produce more surfactant. Without surfactant, alveoli and bronchioles fill with fluid or collapse, gas exchange is impaired, and the lungs are much less compliant. Ventilation of the alveoli is further decreased. The burden of ventilation and gas exchange shifts to uninvolved areas of the lung, and pulmonary blood flow is shunted from right to left. The work of breathing is increased, and the patient may develop thick frothy sputum and marked hypoxemia with increasing respiratory distress.
Mediators released by neutrophils and macrophages also cause varying degrees of pulmonary vasoconstriction, resulting in pulmonary hypertension. The result of these changes is a / mismatch. Although the patient responds with an increased respiratory rate, sufficient oxygen cannot cross the alveolar capillary membrane. Carbon dioxide continues to cross easily and is lost with every exhalation. As both oxygen and carbon dioxide levels in the blood decrease, the patient develops increasing tachypnea, hypoxemia, and hypocapnia (low Pa CO 2 ).
Pulmonary edema worsens and hyaline membranes form. Inflammation leads to fibrosis, which further impedes gas exchange. Fibrosis progressively obliterates alveoli, respiratory bronchioles, and the interstitium. Functional residual capacity decreases and shunting becomes more serious. Hypoxemia leads to metabolic acidosis. At this stage, the patient develops increasing Pa CO 2 , decreasing pH and Pa O 2 , decreasing bicarbonate levels, and mental confusion. (See Looking at adult respiratory distress syndrome .)
The end result is respiratory failure. Systemically, neutrophils and inflammatory mediators cause generalized endothelial damage and increased capillary permeability throughout the body. Multisystem organ dysfunction syndrome (MODS) occurs as the cascade of mediators affects each system. Death may occur from the influence of both ARDS and MODS.
LOOKING AT ADULT RESPIRATORY DISTRESS SYNDROME
|
Signs and symptoms
The following signs and symptoms may occur:
- rapid, shallow breathing and dyspnea, which occur hours to days after the initial injury in response to decreasing oxygen levels in the blood
- increased rate of ventilation due to hypoxemia and its effects on the pneumotaxic center
- intercostal and suprasternal retractions due to the increased effort required to expand the stiff lung
- crackles and rhonchi, which are audible and result from fluid accumulation in the lungs
- restlessness, apprehension, and mental sluggishness, which occur as the result of hypoxic brain cells
- motor dysfunction, which occurs as hypoxia progresses
- tachycardia, which signals the heart's effort to deliver more oxygen to the cells and vital organs
- respiratory acidosis, which occurs as carbon dioxide accumulates in the blood and oxygen levels decrease
- metabolic acidosis, which eventually results from failure of compensatory mechanisms.
Complications
Possible complications of ARDS include:
- hypotension
- decreased urine output
- metabolic acidosis
- respiratory acidosis
- MODS
- ventricular fibrillation
- ventricular standstill.
Diagnosis
The following tests help diagnose ARDS:
- Arterial blood gas (ABG) analysis with the patient breathing room air initially reveals a reduced Pa O 2 (less than 60 mm Hg) and a decreased Pa CO 2 (less than 35 mm Hg). Hypoxemia, despite increased supplemental oxygen, is the hallmark of ARDS; the resulting blood pH reflects respiratory alkalosis. As ARDS worsens, ABG values show respiratory acidosis evident by an increasing Pa CO 2 (over 45 mm Hg), metabolic acidosis evident by a decreasing bicarbonate (HCO 3 less than 22 mEq/L), and a declining Pa O 2 despite oxygen therapy.
- Pulmonary artery catheterization identifies the cause of edema by measuring pulmonary capillary wedge pressure (PCWP of 12 mm Hg or less in ARDS).
- Pulmonary artery mixed venous blood indicates hypoxemia.
- Serial chest X-rays in early stages show bilateral infiltrates; in later stages, lung fields with a ground-glass appearance and “whiteouts” of both lung fields (with irreversible hypoxemia) may be observed.
- Sputum analysis, including Gram stain and culture and sensitivity, identifies causative organisms.
- Blood cultures identify infectious organisms.
- Toxicology testing screens for drug ingestion.
- Serum amylase rules out pancreatitis.
Treatment
Therapy is focused on correcting the causes of ARDS and preventing progression of hypoxemia and respiratory acidosis; it may involve:
- mechanical ventilation and intubation to increase lung volume, open airways, and improve oxygenation
- positive end-expiratory pressure (may be added to increase lung volume and open alveoli)
- pressure-controlled inverse ratio ventilation to reverse the conventional inspiration-to-expiration ratio and minimize the risk of barotrauma (mechanical breaths are pressure-limited to prevent increased damage to the alveoli)
- permissive hypercapnia to limit peak inspiratory pressure (although carbon dioxide removal is compromised, treatment is not given for subsequent changes in blood hydrogen and oxygen concentration)
- sedatives, narcotics, or neuromuscular blockers such as vecuronium bromide, which may be given during mechanical ventilation to minimize restlessness, oxygen consumption, and carbon dioxide production and to facilitate ventilation
- high-dose corticosteroids (may be given when ARDS is due to fatty emboli, to optimize cellular membranes)
- sodium bicarbonate, which may reverse severe metabolic acidosis
- intravenous fluid administration to maintain blood pressure by treating hypovolemia
- vasopressors to maintain blood pressure
- antimicrobial drugs to treat nonviral infections
- diuretics to reduce interstitial and pulmonary edema
- correction of electrolyte and acid-base imbalances to maintain cellular integrity, particularly the sodium-potassium pump
- fluid restriction to prevent increase of interstitial and alveolar edema.
Asbestosis
Considered a form of pneumoconiosis, asbestosis is characterized by diffuse interstitial pulmonary fibrosis. Prolonged exposure to airborne particles causes pleural plaques and tumors of the pleura and peritoneum. Asbestosis may develop 15 to 20 years after regular exposure to asbestos has ended. It is a potent co-carcinogen and increases the smoker's risk for lung cancer. An asbestos worker who smokes is 90 times more likely to develop lung cancer than a smoker who has never worked with asbestos.
Causes
Common causes of this disorder include:
- prolonged inhalation of asbestos fibers; people at high risk include workers in the mining, milling, construction, fireproofing, and textile industries
- asbestos used in paints, plastics, and brake and clutch linings
- family members of asbestos workers who may be exposed to stray fibers from the worker's clothing
- exposure to fibrous asbestos dust in deteriorating buildings or in waste piles from asbestos plants.
Pathophysiology
Asbestosis occurs when lung spaces become filled with asbestos fibers. The inhaled asbestos fibers (about 50 μ × 0.5 μ in size) travel down the airway and penetrate respiratory bronchioles and alveolar walls. Coughing attempts to expel the foreign matter. Mucus production and goblet cells are stimulated to protect the airway from the debris and aid in expectoration. Fibers then become encased in a brown, iron-rich proteinlike sheath in sputum or lung tissue, called asbestosis bodies. Chronic irritation by the fibers continues to affect the lower bronchioles and alveoli. The foreign material and inflammation swell airways, and fibrosis develops in response to the chronic irritation. Interstitial fibrosis may develop in lower lung zones, affecting lung parenchyma and the pleurae. Raised hyaline plaques may form in the parietal pleura, the diaphragm, and the pleura adjacent to the pericardium. Hypoxia develops as more alveoli and lower airways are affected.
Signs and symptoms
The following signs and symptoms may occur:
- dyspnea on exertion
- dyspnea at rest with extensive fibrosis
- severe, nonproductive cough in nonsmokers
- productive cough in smokers
- clubbed fingers due to chronic hypoxia
- chest pain (often pleuritic) due to pleural irritation
- recurrent respiratory tract infections as pulmonary defense mechanisms begin to fail
- pleural friction rub due to fibrosis
- crackles on auscultation attributed to air moving through thickened sputum
- decreased lung inflation due to lung stiffness
- recurrent pleural effusions due to fibrosis
- decreased forced expiratory volume due to diminished alveoli
- decreased vital capacity due to fibrotic changes.
Complications
Possible complications of asbestosis include:
- pulmonary fibrosis due to progression of asbestosis
- respiratory failure
- pulmonary hypertension
- cor pulmonale.
Diagnosis
- Chest X-rays may show fine, irregular, linear, and diffuse infiltrates. Extensive fibrosis is revealed by a honeycomb or ground-glass appearance. Chest X-rays may also show pleural thickening and calcification, bilateral obliteration of the costophrenic angles and, in later stages, an enlarged heart with a classic “shaggy” border.
- Pulmonary function studies may identify decreased vital capacity, forced vital capacity (FVC), and total lung capacity; decreased or normal forced expiratory volume in 1 second (FEV 1 ); a normal ratio, or FEV 1 to FVC; and reduced diffusing capacity for carbon monoxide when fibrosis destroys alveolar walls and thickens the alveolar capillary membrane.
- Arterial blood gas analysis may reveal decreased Pa O 2 and Pa CO 2 from hyperventilation.
Treatment
Asbestosis can't be cured. The goal of treatment is to relieve symptoms and control complications; it may involve:
- chest physiotherapy (such as controlled coughing and postural drainage with chest percussion and vibration) to help relieve respiratory signs and symptoms and manage hypoxia and cor pulmonale
- aerosol therapy to liquefy mucus
- inhaled mucolytics to liquefy and mobilize secretions
- increased fluid intake to 3 L daily
- antibiotics to treat respiratory tract infections
- oxygen administration to relieve hypoxia
- diuretics to decrease inflammation and edema
- digoxin to enhance cardiac output
- salt restriction to prevent fluid retention and thickened secretions.
Asthma
Asthma is a chronic reactive airway disorder causing episodic airway obstruction that results from bronchospasms, increased mucus secretion, and mucosal edema. It is a type of chronic obstructive pulmonary disease (COPD), a long-term pulmonary disease characterized by increased airflow resistance; other types of COPD include chronic bronchitis and emphysema.
Although asthma strikes at any age, about 50% of patients are younger than age 10; twice as many boys as girls are affected in this age group. One-third of patients develops asthma between ages 10 and 30, and the incidence is the same in both sexes in this age group. Moreover, approximately one-third of all patients share the disease with at least one immediate family member.
Asthma may result from sensitivity to extrinsic or intrinsic allergens. Extrinsic, or atopic, asthma begins in childhood; typically, patients are sensitive to specific external allergens.
| AGE ALERT Extrinsic asthma is commonly accompanied by other hereditary allergies, such as eczema and allergic rhinitis, in childhood populations. |
Intrinsic, or nonatopic, asthmatics react to internal, nonallergenic factors; external substances cannot be implicated in patients with intrinsic asthma. Most episodes occur after a severe respiratory tract infection, especially in adults. However, many asthmatics, especially children, have both intrinsic and extrinsic asthma.
| CULTURAL DIVERSITY A significant number of adults acquire an allergic form of asthma or exacerbation of existing asthma from exposure to agents in the workplace. Irritants such as chemicals in flour, acid anhydrides, toluene di-isocyanates, screw flies, river flies, and excreta of dust mites in carpet have been identified as agents that trigger asthma. |
Causes
Extrinsic allergens include:
- pollen
- animal dander
- house dust or mold
- kapok or feather pillows
- food additives containing sulfites
- other sensitizing substances.
Intrinsic allergens include:
- irritants
- emotional stress
- fatigue
- endocrine changes
- temperature variations
- humidity variations
- exposure to noxious fumes
- anxiety
- coughing or laughing
- genetic factors (see below).
Pathophysiology
There are two genetic influences identified with asthma, namely the ability of an individual to develop asthma (atopy) and the tendency to develop hyperresponsiveness of the airways independent of atopy. A locus of chromosome 11 associated with atopy contains an abnormal gene that encodes a part of the immunoglobulin E (IgE) receptor. Environmental factors interact with inherited factors to cause asthmatic reactions with associated bronchospasms.
In asthma, bronchial linings overreact to various stimuli, causing episodic smooth muscle spasms that severely constrict the airways. (See Pathophysiology of asthma .) IgE antibodies, attached to histamine-containing mast cells and receptors on cell membranes, initiate intrinsic asthma attacks. When exposed to an antigen such as pollen, the IgE antibody combines with the antigen.
On subsequent exposure to the antigen, mast cells degranulate and release mediators. Mast cells in the lung interstitium are stimulated to release both histamine and the slow-reacting substance of anaphylaxis. Histamine attaches to receptor sites in the larger bronchi, where it causes swelling in smooth muscles. Mucous membranes become inflamed, irritated, and swollen. The patient may experience dyspnea, prolonged expiration, and an increased respiratory rate.
The slow-reacting substance of anaphylaxis (SRS-A) attaches to receptor sites in the smaller bronchi and causes local swelling of the smooth muscle. SRS-A also causes prostaglandins to travel via the bloodstream to the lungs, where they enhance the effect of histamine. A wheeze may be audible during coughing; the higher the pitch, the narrower is the bronchial lumen. Histamine stimulates the mucous membranes to secrete excessive mucus, further narrowing the bronchial lumen. Goblet cells secrete viscous mucus that is difficult to cough up, resulting in coughing, rhonchi, increased-pitch wheezing, and increased respiratory distress. Mucosal edema and thickened secretions further block the airways. (See Looking at a bronchiole in asthma .)
On inhalation, the narrowed bronchial lumen can still expand slightly, allowing air to reach the alveoli. On exhalation, increased intrathoracic pressure closes the bronchial lumen completely. Air enters but cannot escape. The patient develops a barrel chest and hyperresonance to percussion.
Mucus fills the lung bases, inhibiting alveolar ventilation. Blood is shunted to alveoli in other lung parts, but still can't compensate for diminished ventilation.
PATHOPHYSIOLOGY OF ASTHMA
|
Hyperventilation is triggered by lung receptors to increase lung volume because of trapped air and obstructions. Intrapleural and alveolar gas pressures rise, causing a decreased perfusion of alveoli. Increased alveolar gas pressure, decreased ventilation, and decreased perfusion result in uneven / ratios and mismatching within different lung segments.
Hypoxia triggers hyperventilation by stimulation of the respiratory center, which in turn decreases Pa CO 2 and increases pH, resulting in a respiratory alkalosis. As the obstruction to the airways increases in severity, more alveoli are affected. Ventilation and perfusion remain inadequate, and CO 2 retention develops. Respiratory acidosis results and respiratory failure occurs.
|
LOOKING AT A BRONCHIOLE IN ASTHMA
Asthma is characterized by bronchospasms, increased mucus secretion, and mucosal edema, which contribute to airway narrowing and obstruction. Shown below is a normal bronchiole in cross section and an obstructed bronchiole, as it occurs in asthma. <center></center> |
If status asthmaticus occurs, hypoxia worsens and expiratory flows and volumes decrease even further. If treatment is not initiated, the patient begins to tire out. (See Averting an asthma attack .) Acidosis develops as arterial carbon dioxide increases. The situation becomes life-threatening as no air becomes audible upon auscultation (a silent chest) and Pa CO 2 rises to over 70 mm Hg.
Signs and symptoms
Patients with mild asthma have adequate air exchange and are asymptomatic between attacks; they may have the following signs and symptoms:
- wheezing due to edema of the airways
- coughing due to stimulation of the cough reflex to eliminate the lungs of excess mucus and irritants
- histamine-induced production of thick, clear, or yellow mucus
- dyspnea on exertion due to narrowing of airways and inability to take in the increased oxygen that is required for exercise.
Patients with moderate asthma have normal or below normal air exchange and may exhibit:
- respiratory distress at rest due to narrowed airways and decreased oxygenation to the tissues
- hyperpnea (abnormal increase in the depth and rate of respiration) due to the body's attempt to take in more oxygen
- barrel chest due to air trapping and retention
- diminished breath sounds due to air trapping.
Patients with severe asthma have continuous signs and symptoms that include:
- marked respiratory distress due to failure of compensatory mechanisms and decreased oxygenation levels
- marked wheezing due to increased edema and increased mucus in the lower airways
- absent breath sounds due to severe bronchoconstriction and edema
- pulsus paradoxus greater than 10 mm Hg
- chest wall contractions due to use of accessory muscles.
|
AVERTING AN ASTHMA ATTACK
The following flow chart shows pathophysiologic changes that occur with asthma. Treatments and interventions show where the physiologic cascade would be altered to stop an asthma attack. <center></center> |
Complications
Possible complications include:
- status asthmaticus
- respiratory failure.
Diagnosis
The following tests help diagnose asthma:
- Pulmonary function studies reveal signs of airway obstructive disease, low-normal or decreased vital capacity, and increased total lung and residual capacities. Pulmonary function may be normal between attacks. Pa O 2 and Pa CO 2 usually are decreased, except in severe asthma, when Pa CO 2 may be normal or increased, indicating severe bronchial obstruction.
- Serum IgE levels may increase from an allergic reaction.
- Sputum analysis may indicate presence of Curschmann's spirals (casts of airways), Charcot-Leyden crystals, and eosinophils.
- Complete blood count with differential reveals increased eosinophil count.
- Chest X-rays can be used to diagnose or monitor the progress of asthma and may show hyperinflation with areas of atelectasis.
- Arterial blood gas analysis detects hypoxemia (decreased Pa O 2 ; decreased, normal, or increasing Pa CO 2 ) and guides treatment.
- Skin testing may identify specific allergens; results read in 1 or 2 days detect an early reaction, and after 4 or 5 days reveal a late reaction.
- Bronchial challenge testing evaluates the clinical significance of allergens identified by skin testing.
- Electrocardiography shows sinus tachycardia during an attack; severe attack may show signs of cor pulmonale (right axis deviation, peaked P wave) that resolve after the attack.
Treatment
Correcting asthma typically involves:
- prevention, by identifying and avoiding precipitating factors such as environmental allergens or irritants, which is the best treatment
- desensitization to specific antigens ― helpful if the stimuli can't be removed entirely ― which decreases the severity of attacks of asthma with future exposure
- bronchodilators (such as theophylline, aminophylline, epinephrine, albuterol, metaproterenol, and terbutaline) to decrease bronchoconstriction, reduce bronchial airway edema, and increase pulmonary ventilation
- corticosteroids (such as hydrocortisone and methylprednisolone) to decrease bronchoconstriction, reduce bronchial airway edema, and increase pulmonary ventilation
- subcutaneous epinephrine to counteract the effects of mediators of an asthma attack
- mast cell stabilizers (cromolyn sodium and nedocromil sodium), effective in patients with atopic asthma who have seasonal disease. When given prophylactically, they block the acute obstructive effects of antigen exposure by inhibiting the degranulation of mast cells, thereby preventing the release of chemical mediators responsible for anaphylaxis
- low-flow humidified oxygen, which may be needed to treat dyspnea, cyanosis, and hypoxemia. However, the amount delivered should maintain Pa O 2 between 65 and 85 mm Hg, as determined by arterial blood gas analysis
- mechanical ventilation ― necessary if the patient doesn't respond to initial ventilatory support and drugs, or develops respiratory failure
- relaxation exercises such as yoga to help increase circulation and to help a patient recover from an asthma attack.
Chronic bronchitis
Chronic bronchitis is inflammation of the bronchi caused by irritants or infection. A form of chronic obstructive pulmonary disease (COPD), bronchitis may be classified as acute or chronic. In chronic bronchitis, hypersecretion of mucus and chronic productive cough last for 3 months of the year and occur for at least 2 consecutive years. The distinguishing characteristic of bronchitis is obstruction of airflow.
|
CHANGES IN CHRONIC BRONCHITIS
In chronic bronchitis, irritants inflame the tracheobronchial tree over time, leading to increased mucus production and a narrowed or blocked airway. As the inflammation continues, goblet and epithelial cells hypertrophy. Because the natural defense mechanisms are blocked, the airways accumulate debris in the respiratory tract. Shown below is a cross section of these changes. <center></center> |
| CULTURAL DIVERSITY COPD is more prevalent in an urban versus rural environment, and is also related to occupational factors (mineral or organic dusts). |
| AGE ALERT Children of parents who smoke are at higher risk for respiratory tract infection that can lead to chronic bronchitis. |
Causes
Common causes of chronic bronchitis include:
- exposure to irritants
- cigarette smoking
- genetic predisposition
- exposure to organic or inorganic dusts
- exposure to noxious gases
- respiratory tract infection.
Pathophysiology
Chronic bronchitis occurs when irritants are inhaled for a prolonged time. The irritants inflame the tracheobronchial tree, leading to increased mucus production and a narrowed or blocked airway. As the inflammation continues, changes in the cells lining the respiratory tract result in resistance of the small airways and severe / imbalance, which decreases arterial oxygenation.
Chronic bronchitis results in hypertrophy, hyperplasia of the mucous glands, increased goblet cells, ciliary damage, squamous metaplasia of the columnar epithelium, and chronic leukocytic and lymphocytic infiltration of bronchial walls. (See Changes in chronic bronchitis .) Hypersecretion of the goblet cells blocks the free movement of the cilia, which normally sweep dust, irritants, and mucus away from the airways. With mucus and debris accumulating in the airway, the defenses are altered, and the individual is prone to respiratory tract infections.
Additional effects include widespread inflammation, airway narrowing, and mucus within the airways. Bronchial walls become inflamed and thickened from edema and accumulation of inflammatory cells, and the effects of smooth muscle bronchospasm further narrow the lumen. Initially, only large bronchi are involved but eventually, all airways are affected. Airways become obstructed and closure occurs, especially on expiration. The gas is then trapped in the distal portion of the lung. Hypoventilation occurs, leading to a / mismatch and resultant hypoxemia.
Hypoxemia and hypercapnia occur secondary to hypoventilation. Pulmonary vascular resistance (PVR) increases as inflammatory and compensatory vasoconstriction in hypoventilated areas narrows the pulmonary arteries. Increased PVR leads to increased afterload of the right ventricle. With repeated inflammatory episodes, scarring of the airways occurs and permanent structural changes develop. Respiratory infections can trigger acute exacerbations, and respiratory failure can occur.
Patients with chronic bronchitis have a diminished respiratory drive. The resulting chronic hypoxia causes the kidneys to produce erythropoietin, which stimulates excessive red blood cell production and leads to polycythemia. Although hemoglobin levels are high, the amount of reduced (not fully oxygenated) hemoglobin that is in contact with oxygen is low; therefore, cyanosis occurs.
Signs and symptoms
The following signs and symptoms may occur:
- copious gray, white, or yellow sputum due to hypersecretion of goblet cells
- productive cough to expectorate mucus that is produced by the lungs
- dyspnea due to obstruction of airflow to the lower tracheobronchial tree
- cyanosis related to diminished oxygenation and cellular hypoxia; reduced oxygen is supplied to the tissues
- use of accessory muscles for breathing due to compensated attempts to supply the cells with increased oxygen
- tachypnea due to hypoxia
- pedal edema due to right-sided heart failure
- neck vein distention due to right-sided heart failure
- weight gain due to edema
- wheezing due to air moving through narrowed respiratory passages
- prolonged expiratory time due to the body's attempt to keep airways patent
- rhonchi due to air moving through narrow, mucus-filled passages
- pulmonary hypertension caused by involvement of small pulmonary arteries, due to inflammation in the bronchial walls and spasms of pulmonary blood vessels from hypoxia.
Complications
Possible complications of this disorder include:
- cor pulmonale (right ventricular hypertrophy with right-sided heart failure) due to increased right ventricular end-diastolic pressure
- pulmonary hypertension
- heart failure, resulting in increased venous pressure, liver engorgement, and dependent edema
- acute respiratory failure.
Diagnosis
The following tests help diagnose chronic bronchitis:
- Chest X-rays may show hyperinflation and increased bronchovascular markings.
- Pulmonary function studies indicate increased residual volume, decreased vital capacity and forced expiratory flow, and normal static compliance and diffusing capacity.
- Arterial blood gas analysis reveals decreased Pa O 2 and normal or increased Pa CO 2 .
- Sputum analysis may reveal many microorganisms and neutrophils.
- Electrocardiography may show atrial arrhythmias; peaked P waves in leads II, III, and aV F ; and occasionally, right ventricular hypertrophy.
Treatment
Correcting chronic bronchitis typically involves:
- avoidance of air pollutants (most effective)
- smoking cessation
- antibiotics to treat recurring infections
- bronchodilators to relieve bronchospasms and facilitate mucociliary clearance
- adequate hydration to liquefy secretions
- chest physiotherapy to mobilize secretions
- ultrasonic or mechanical nebulizers to loosen and mobilize secretions
- corticosteroids to combat inflammation
- diuretics to reduce edema
- oxygen to treat hypoxia.
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD), also called chronic obstructive lung disease (COLD), results from emphysema, chronic bronchitis, asthma, or a combination of these disorders. Usually, more than one of these underlying conditions coexist; bronchitis and emphysema often occur together. (See “ Asthma ,” “ Chronic bronchitis ,” and “ Emphysema ” for a review of these conditions.)
COPD is the most common lung disease and affects an estimated 17 million Americans; the incidence is rising. The disease is not always symptomatic and may cause only minimal disability. However, COPD worsens with time.
Causes
Common causes of COPD may include:
- cigarette smoking
- recurrent or chronic respiratory tract infections
- air pollution
- allergies
- familial and hereditary factors such as deficiency of alpha 1 -antitrypsin.
Pathophysiology
Smoking, one of the major causes of COPD, impairs ciliary action and macrophage function and causes inflammation in the airways, increased mucus production, destruction of alveolar septa, and peribronchiolar fibrosis. Early inflammatory changes may reverse if the patient stops smoking before lung disease becomes extensive.
The mucus plugs and narrowed airways cause air trapping, as in chronic bronchitis and emphysema. Hyperinflation occurs to the alveoli on expiration. On inspiration, airways enlarge, allowing air to pass beyond the obstruction; on expiration, airways narrow and gas flow is prevented. Air trapping (also called ball valving) occurs commonly in asthma and chronic bronchitis. (See Air trapping in chronic obstructive pulmonary disease .)
Signs and symptoms
The following signs and symptoms may occur:
- reduced ability to perform exercises or do strenuous work due to diminished pulmonary reserve
- productive cough due to stimulation of the reflex by mucus
- dyspnea on minimal exertion
- frequent respiratory tract infections
- intermittent or continuous hypoxemia
- grossly abnormal pulmonary function studies
- thoracic deformities.
Complications
Possible complications of COPD include:
- overwhelming disability
- cor pulmonale
- severe respiratory failure
- death.
|
AIR TRAPPING IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE
In chronic obstructive pulmonary disease, mucus plugs and narrowed airways trap air (also called ball valving). During inspiration, the airways enlarge and gas enters; on expiration, the airways narrow and air can't escape. This commonly occurs in asthma and chronic bronchitis. <center></center> |
Diagnosis
The following tests help diagnose COPD:
- Arterial blood gas analysis determines oxygen need by indicating degree of hypoxia and helps avoid carbon dioxide narcosis.
- Chest X-rays support underlying diagnosis.
- Pulmonary function studies support diagnosis of underlying condition.
- Electrocardiography may show arrhythmias consistent with hypoxemia.
Treatment
Managing COPD typically involves:
- bronchodilators to alleviate bronchospasms and enhance mucociliary clearance of secretions
- effective coughing to remove secretions
- postural drainage to help mobilize secretions
- chest physiotherapy to mobilize secretions
- low oxygen concentrations as needed (high flow rates of O 2 can lead to narcosis)
- antibiotics to allow treatment of respiratory tract infections
- pneumococcal vaccination and annual influenza vaccinations as important preventive measures
- smoking cessation
- installation in the home of an air conditioner with an air filter and avoidance of allergens, which may be helpful
- increased fluid intake to thin mucus
- use of a humidifier to thin secretions.
Cor pulmonale
Cor pulmonale (also called right ventricular failure) is a condition in which hypertrophy and dilation of the right ventricle develop secondary to disease affecting the structure or function of the lungs or their vasculature. It can occur at the end stage of various chronic disorders of the lungs, pulmonary vessels, chest wall, and respiratory control center. Cor pulmonale doesn't occur with disorders stemming from congenital heart disease or with those affecting the left side of the heart.
| CULTURAL DIVERSITY Cor pulmonale is more prevalent in countries where the incidence of obstructive lung disease is high, such as in the United Kingdom. |
About 85% of patients with cor pulmonale also have chronic obstructive pulmonary disease (COPD), and about 25% of patients with bronchial COPD eventually develop cor pulmonale. The disorder is most common in smokers and in middle-aged and elderly males; however, its incidence in females is rising. Because cor pulmonale occurs late in the course of the individual's underlying condition and with other irreversible diseases, the prognosis is poor.
| AGE ALERT In children, cor pulmonale may be a complication of cystic fibrosis, hemosiderosis, upper airway obstruction, scleroderma, extensive bronchiectasis, neuromuscular diseases that affect respiratory muscles, or abnormalities of the respiratory control area. |
Causes
Common causes of cor pulmonale include:
- disorders that affect the pulmonary parenchyma
- COPD
- bronchial asthma
- primary pulmonary hypertension
- vasculitis
- pulmonary emboli
- external vascular obstruction resulting from a tumor or aneurysm
- kyphoscoliosis
- pectus excavatum (funnel chest)
- muscular dystrophy
- poliomyelitis
- obesity
- high altitude.
Pathophysiology
In cor pulmonale, pulmonary hypertension increases the heart's workload. To compensate, the right ventricle hypertrophies to force blood through the lungs. As long as the heart can compensate for the increased pulmonary vascular resistance, signs and symptoms reflect only the underlying disorder.
Severity of right ventricular enlargement in cor pulmonale is due to increased afterload. An occluded vessel impairs the heart's ability to generate enough pressure. Pulmonary hypertension results from the increased blood flow needed to oxygenate the tissues.
In response to hypoxia, the bone marrow produces more red blood cells, causing polycythemia. The blood's viscosity increases, which further aggravates pulmonary hypertension. This increases the right ventricle's workload, causing heart failure. (See Cor pulmonale: An overview .)
In chronic obstructive disease, increased airway obstruction makes airflow worse. The resulting hypoxia and hypercarbia can have vasodilatory effects on systemic arterioles. However, hypoxia increases pulmonary vasoconstriction. The liver becomes palpable and tender because it is engorged and displaced downward by the low diaphragm. Hepatojugular reflux may occur.
Compensatory mechanisms begin to fail and larger amounts of blood remain in the right ventricle at the end of diastole, causing ventricular dilation. Increasing intrathoracic pressures impede venous return and raise jugular venous pressure. Peripheral edema can occur and right ventricular hypertrophy increases progressively. The main pulmonary arteries enlarge, pulmonary hypertension increases, and heart failure occurs.
|
COR PULMONALE: AN OVERVIEW
Although pulmonary restrictive disorders (such as fibrosis or obesity), obstructive disorders (such as bronchitis), or primary vascular disorders (such as recurrent pulmonary emboli) may cause cor pulmonale, these disorders share the following common pathway. <center></center> |
Signs and symptoms
Patients in early stages of cor pulmonale may present with:
- chronic productive cough to clear secretions from the lungs
- exertional dyspnea due to hypoxia
- wheezing respirations as airways narrow
- fatigue and weakness due to hypoxemia.
Patients with progressive cor pulmonale may present with:
- dyspnea at rest due to hypoxemia
- tachypnea due to response to decreased oxygenation to the tissues
- orthopnea due to pulmonary edema
- dependent edema due to right-sided heart failure
- distended neck veins due to pulmonary hypertension
- enlarged, tender liver related to polycythemia and decreased cardiac output
- hepatojugular reflux (distention of the jugular vein induced by pressing over the liver) due to right-sided heart failure
- right upper quadrant discomfort due to liver involvement
- tachycardia due to decreased cardiac output and increasing hypoxia
- weakened pulses due to decreased cardiac output
- decreased cardiac output
- pansystolic murmur at the lower left sternal border with tricuspid insufficiency, which increases in intensity when the patient inhales.
Complications
Possible complications of cor pulmonale include:
- biventricular failure as the heart hypertrophies in an attempt to circulate the blood
- hepatomegaly
- edema
- ascites
- pleural effusions
- thromboembolism due to polycythemia.
Diagnosis
The following tests help diagnose cor pulmonale:
- Pulmonary artery catheterization shows increased right ventricular and pulmonary artery pressures, resulting from increased pulmonary vascular resistance. Both right ventricular systolic and pulmonary artery systolic pressures are over 30 mm Hg, and pulmonary artery diastolic pressure is higher than 15 mm Hg.
- Echocardiography demonstrates right ventricular enlargement.
- Angiography shows right ventricular enlargement.
- Chest X-rays reveal large central pulmonary arteries and right ventricular enlargement.
- Arterial blood gas analysis detects decreased Pa O 2 (usually less than 70 mm Hg and rarely more than 90 mm Hg).
- Electrocardiography shows arrhythmias, such as premature atrial and ventricular contractions and atrial fibrillation during severe hypoxia, and also right bundle branch block, right axis deviation, prominent P waves, and an inverted T wave in right precordial leads.
- Pulmonary function studies reflect underlying pulmonary disease.
- Magnetic resonance imaging measures right ventricular mass, wall thickness, and ejection fraction.
- Cardiac catheterization measures pulmonary vascular pressures.
- Laboratory testing may reveal hematocrit typically over 50%; serum hepatic tests may show an elevated level of aspartate aminotransferase levels with hepatic congestion and decreased liver function, and serum bilirubin levels may be elevated if liver dysfunction and hepatomegaly exist.
Treatment
Therapy of cor pulmonale has three aims: reducing hypoxemia and pulmonary vasoconstriction, increasing exercise tolerance, and correcting the underlying condition when possible. Treatment may involve:
- bed rest to reduce myocardial oxygen demands
- digoxin to increase the strength of contraction of the myocardium
- antibiotics to treat an underlying respiratory tract infection
- a potent pulmonary artery vasodilator, such as diazoxide, nitroprusside, or hydralazine, to reduce primary pulmonary hypertension
- continuous administration of low concentrations of oxygen to decrease pulmonary hypertension, polycythemia, and tachypnea
- mechanical ventilation to reduce the workload of breathing in the acute disease
- a low-sodium diet with restricted fluid to reduce edema
- phlebotomy to decrease excess red blood cell mass that occurs with polycythemia
- small doses of heparin to decrease the risk of thromboembolism
- tracheotomy, which may be required if the patient has an upper airway obstruction
- corticosteroids to treat vasculitis or an underlying autoimmune disorder.
Emphysema
Emphysema, a form of chronic obstructive pulmonary disease, is the abnormal, permanent enlargement of the acini accompanied by destruction of alveolar walls. Obstruction results from tissue changes rather than mucus production, which occurs with asthma and chronic bronchitis. The distinguishing characteristic of emphysema is airflow limitation caused by lack of elastic recoil in the lungs.
Emphysema appears to be more prevalent in males than females; about 65% of patients with well-defined emphysema are men and 35% are women.
| AGE ALERT Aging is a risk factor for emphysema. Senile emphysema results from degenerative changes; stretching occurs without destruction in the smooth muscle. Connective tissue is not usually affected. |
Causes
Emphysema is usually caused by:
- deficiency of alpha 1 -antitrypsin
- cigarette smoking.
Pathophysiology
Primary emphysema has been linked to an inherited deficiency of the enzyme alpha 1 -antitrypsin, a major component of alpha 1 -globulin. Alpha 1 -antitrypsin inhibits the activation of several proteolytic enzymes; deficiency of this enzyme is an autosomal recessive trait that predisposes an individual to develop emphysema because proteolysis in lung tissues is not inhibited. Homozygous individuals have up to an 80% chance of developing lung disease; if the individual smokes, he has a greater chance of developing emphysema. Patients who develop emphysema before or during their early forties and those who are nonsmokers are believed to have a deficiency of alpha 1 -antitrypsin.
In emphysema, recurrent inflammation is associated with the release of proteolytic enzymes from lung cells. This causes irreversible enlargement of the air spaces distal to the terminal bronchioles. Enlargement of air spaces destroys the alveolar walls, which results in a breakdown of elasticity and loss of fibrous and muscle tissue, thus making the lungs less compliant.
In normal breathing, the air moves into and out of the lungs to meet metabolic needs. A change in airway size compromises the ability of the lungs to circulate sufficient air. In patients with emphysema, recurrent pulmonary inflammation damages and eventually destroys the alveolar walls, creating large air spaces. (See A look at abnormal alveoli .) The alveolar septa are initially destroyed, eliminating a portion of the capillary bed and increasing air volume in the acinus. This breakdown leaves the alveoli unable to recoil normally after expanding and results in bronchiolar collapse on expiration. The damaged or destroyed alveolar walls cannot support the airways to keep them open. (See Air trapping in emphysema .) The amount of air that can be expired passively is diminished, thus trapping air in the lungs and leading to overdistention. Hyperinflation of the alveoli produces bullae (air spaces) and air spaces adjacent to the pleura (blebs). Septal destruction also decreases airway calibration. Part of each inspiration is trapped due to increased residual volume and decreased calibration. Septal destruction may affect only the respiratory bronchioles and alveolar ducts, leaving alveolar sacs intact (centriacinar emphysema), or it can involve the entire acinus (panacinar emphysema), with damage more random and involving the lower lobes of the lungs.
| AGE ALERT Panacinar emphysema tends to occur in the elderly with alpha 1 -antitrypsin deficiency, whereas centriacinar emphysema occurs in smokers with chronic bronchitis. |
Associated pulmonary capillary destruction usually allows a patient with severe emphysema to match ventilation to perfusion. This process prevents the development of cyanosis. The lungs are usually enlarged; therefore, the total lung capacity and residual volume increase.
|
A LOOK AT ABNORMAL ALVEOLI
In the patient with emphysema, recurrent pulmonary inflammation damages and eventually destroys the alveolar walls, creating large air spaces. The damaged alveoli can't recoil normally after expanding, and so bronchioles collapse on expiration, trapping air in the lungs and causing overdistention. As the alveolar walls are destroyed, the lungs become enlarged, and the total lung capacity and residual volume then increase. Shown below are changes that occur during emphysema. <center></center> |
Signs and symptoms
The following signs and symptoms may occur:
- tachypnea related to decreased oxygenation
- dyspnea on exertion, which is often the initial symptom
- barrel-shaped chest due to the lungs overdistending and overinflating
- prolonged expiration and grunting, which occur because the accessory muscles are used for inspiration and abdominal muscles are used for expiration
- decreased breath sounds due to air-trapping in the alveoli and destruction of alveoli
- clubbed fingers and toes related to chronic hypoxic changes
- decreased tactile fremitus on palpation as air moves through poorly functional alveoli
- decreased chest expansion due to hypoventilation
- hyperresonance on chest percussion due to overinflated air spaces
- crackles and wheezing on inspiration as bronchioles collapse.
Complications
Possible complications of emphysema include:
- right ventricular hypertrophy (cor pulmonale)
- respiratory failure
- recurrent respiratory tract infections.
Diagnosis
- Chest X-rays in advanced disease may show a flattened diaphragm, reduced vascular markings at the lung periphery, overaeration of the lungs, a vertical heart, enlarged anteroposterior chest diameter, and large retrosternal air space.
- Pulmonary function studies indicate increased residual volume and total lung capacity, reduced diffusing capacity, and increased inspiratory flow.
- Arterial blood gas analysis usually reveals reduced Pa O 2 and a normal Pa CO 2 until late in the disease process.
- Electrocardiography may show tall, symmetrical P waves in leads II, III, and aV F ; vertical QRS axis and signs of right ventricular hypertrophy are seen late in the disease.
- Complete blood count usually reveals an increased hemoglobin level late in the disease when the patient has persistent severe hypoxia.
|
AIR TRAPPING IN EMPHYSEMA
Once alveolar walls are damaged or destroyed, they can't support and keep the airways open. The alveolar walls then lose their capability of elastic recoil. Collapse then occurs on expiration, as shown below. <center></center> |
Treatment
Correcting this disorder typically involves:
- avoiding smoking to preserve remaining alveoli
- avoiding air pollution to preserve remaining alveoli
- bronchodilators, such as beta-adrenergic blockers and albuterol and ipratropium bromide, to reverse bronchospasms and promote mucociliary clearance
- antibiotics to treat respiratory tract infections
- pneumovax to prevent pneumococcal pneumonia
- adequate hydration to liquefy and mobilize secretions
- chest physiotherapy to mobilize secretions
- oxygen therapy at low settings to correct hypoxia
- flu vaccine to prevent influenza
- mucolytics to thin secretions and aid in expectoration of mucus
- aerosolized or systemic corticosteroids
- transtracheal catheterization to enable the patient to receive oxygen therapy at home.
Idiopathic respiratory distress syndrome of the newborn
Also known as respiratory distress syndrome (RDS) and hyaline membrane disease, this disorder is the most common cause of neonatal death; in the United States alone, it kills about 40,000 newborns every year.
| AGE ALERT The syndrome occurs most exclusively in infants born before 37 weeks' gestation; it occurs in about 60% of those born before gestational week 28. |
Idiopathic respiratory distress syndrome (IRDS) of the newborn is marked by widespread alveolar collapse. Occurring mainly in premature infants and in sudden infant death syndrome, it strikes apparently healthy infants. It is most common in infants of diabetic mothers and in those delivered by cesarean section, or it may occur suddenly after antepartum hemorrhage.
In IRDS of the newborn, the premature infant develops a widespread alveolar collapse due to surfactant deficiency. If untreated, the syndrome causes death within 72 hours of birth in up to 14% of infants weighing under 5.5 lbs (2,500 g). Aggressive management and mechanical ventilation can improve the prognosis, although some surviving infants are left with bronchopulmonary dysplasia. Mild cases of the syndrome subside after about 3 days.
Causes
Common causes of this syndrome include:
- lack of surfactant
- premature birth.
Pathophysiology
Surfactant, a lipoprotein present in alveoli and respiratory bronchioles, helps to lower surface tension, maintain alveolar patency, and prevent alveolar collapse, particularly at the end of expiration.
Although the neonatal airways are developed by gestational week 27, the intercostal muscles are weak, and the alveoli and capillary blood supply are immature. Surfactant deficiency causes a higher surface tension. The alveoli are not allowed to maintain patency and begin to collapse.
With alveolar collapse, ventilation is decreased and hypoxia develops. The resulting pulmonary injury and inflammatory reaction lead to edema and swelling of the interstitial space, thus impeding gas exchange between the capillaries and the functional alveoli. The inflammation also stimulates production of hyaline membranes composed of white fibrin accumulation in the alveoli. These deposits further reduce gas exchange in the lung and decrease lung compliance, resulting in increased work of breathing.
Decreased alveolar ventilation results in decreased / ratio and pulmonary arteriolar vasoconstriction. The pulmonary vasoconstriction can result in increased right cardiac volume and pressure, causing blood to be shunted from the right atrium through a patent foramen ovale to the left atrium. Increased pulmonary resistance also results in deoxygenated blood passing through the ductus arteriosus, totally bypassing the lungs, and causing a right-to-left shunt. The shunt further increases hypoxia.
Because of immature lungs and an already increased metabolic rate, the infant must expend more energy to ventilate collapsed alveoli. This further increases oxygen demand and contributes to cyanosis. The infant attempts to compensate with rapid shallow breathing, causing an initial respiratory alkalosis as carbon dioxide is expelled. The increased effort at lung expansion causes respirations to slow and respiratory acidosis to occur, leading to respiratory failure.
Signs and symptoms
The following signs and symptoms may occur:
| AGE ALERT Suspect idiopathic respiratory distress syndrome of the newborn in a patient with a history that includes preterm birth (before gestational week 28), cesarean delivery, maternal history of diabetes, or antepartal hemorrhage. |
- rapid, shallow respirations due to hypoxia
- intercostal, subcostal, or sternal retractions due to hypoxia
- nasal flaring due to hypoxia
- audible expiratory grunting; the grunting is a natural compensatory mechanism that produces positive end-expiratory pressure (PEEP) to prevent further alveolar collapse
- hypotension due to cardiac failure
- peripheral edema due to cardiac failure
- oliguria due to vasoconstriction of kidneys.
In severe cases, the following may also occur:
- apnea due to respiratory failure
- bradycardia due to cardiac failure
- cyanosis from hypoxemia, right-to-left shunting through the foramen ovale, or right-to-left shunting through the atelectatic lung areas
- pallor due to decreased circulation
- frothy sputum due to pulmonary edema and atelectasis
- low body temperature, resulting from an immature nervous system and inadequate subcutaneous fat
- diminished air entry and crackles on auscultation due to atelectasis.
Complications
Possible complications include:
- respiratory failure
- cardiac failure
- bronchopulmonary dysplasia.
Diagnosis
The following tests help diagnose IRDS:
- Chest X-rays may be normal for the first 6 to 12 hours in 50% of patients, although later films show a fine reticulonodular pattern and dark streaks, indicating air-filled, dilated bronchioles.
- Arterial blood gas analysis reveals a diminished Pa O 2 level; a normal, decreased, or increased Pa CO 2 level; and a reduced pH, indicating a combination of respiratory and metabolic acidosis.
- Lecithin-sphingomyelin ratio helps to assess prenatal lung development and infants at risk for this syndrome; this test is usually ordered if a cesarean section will be performed before gestational week 36.
Treatment
Correcting this syndrome typically involves:
- warm, humidified, oxygen-enriched gases administered by oxygen hood or, if such treatment fails, by mechanical ventilation to promote adequate oxygenation and reverse hypoxia
- mechanical ventilation with PEEP or continuous positive airway pressure (CPAP) administered by a tight-fitting face mask or endotracheal tube; this forces the alveoli to remain open on expiration and promotes increased surface area for exchange of oxygen and carbon dioxide
- high-frequency oscillation ventilation if the neonate can't maintain adequate gas exchange; this provides satisfactory minute volume (the total air breathed in 1 minute) with lower airway pressures
- radiant warmer or an Isolette to help maintain thermoregulation and reduce metabolic demands
- intravenous fluids to promote adequate hydration and maintain circulation with capillary refill of less than 2 seconds; fluid and electrolyte balance is also maintained
- sodium bicarbonate to control acidosis
- tube feedings or total parenteral nutrition to maintain adequate nutrition if the neonate is too weak to eat
- drug therapy with pancuronium bromide, a paralytic agent, preventing spontaneous respiration during mechanical ventilation
- prophylactic antibiotics for underlying infections
- diuretics to reduce pulmonary edema
- synthetic surfactant to prevent atelectasis and maintain alveolar integrity
- vitamin E to prevent complications associated with oxygen therapy
| AGE ALERT Corticosteroids may be administered to the mother to stimulate surfactant production in a fetus at high risk for preterm birth. |
- delayed delivery of an infant (if premature labor) to possibly prevent idiopathic respiratory distress syndrome.
Pneumothorax
Pneumothorax is an accumulation of air in the pleural cavity that leads to partial or complete lung collapse. When the air between the visceral and parietal pleurae collects and accumulates, increasing tension in the pleural cavity can cause the lung to progressively collapse. Air is trapped in the intrapleural space and determines the degree of lung collapse. Venous return to the heart may be impeded to cause a life-threatening condition called tension pneumothorax.
The most common types of pneumothorax are open, closed, and tension.
Causes
Common causes of open pneumothorax include:
- penetrating chest injury (gunshot or stab wound)
- insertion of a central venous catheter
- chest surgery
- transbronchial biopsy
- thoracentesis or closed pleural biopsy.
Causes of closed pneumothorax include:
- blunt chest trauma
- air leakage from ruptured blebs
- rupture resulting from barotrauma caused by high intrathoracic pressures during mechanical ventilation
- tubercular or cancerous lesions that erode into the pleural space
- interstitial lung disease, such as eosinophilic granuloma.
Tension pneumothorax may be caused by:
- penetrating chest wound treated with an air-tight dressing
- fractured ribs
- mechanical ventilation
- high-level positive end-expiratory pressure that causes alveolar blebs to rupture
- chest tube occlusion or malfunction.
Pathophysiology
A rupture in the visceral or parietal pleura and chest wall causes air to accumulate and separate the visceral and parietal pleurae. Negative pressure is destroyed and the elastic recoil forces are affected. The lung recoils by collapsing toward the hilus.
Open pneumothorax (also called sucking chest wound or communicating pneumothorax) results when atmospheric air (positive pressure) flows directly into the pleural cavity (negative pressure). As the air pressure in the pleural cavity becomes positive, the lung collapses on the affected side, resulting in decreased total lung capacity, vital capacity, and lung compliance. / imbalances lead to hypoxia.
Closed pneumothorax occurs when air enters the pleural space from within the lung, causing increased pleural pressure, which prevents lung expansion during normal inspiration. Spontaneous pneumothorax is another type of closed pneumothorax.
| AGE ALERT Spontaneous pneumothorax is common in older patients with chronic pulmonary disease, but it may also occur in healthy, tall, young adults. |
Both types of closed pneumothorax can result in a collapsed lung with hypoxia and decreased total lung capacity, vital capacity, and lung compliance. The range of lung collapse is between 5% and 95%.
Tension pneumothorax results when air in the pleural space is under higher pressure than air in the adjacent lung. The air enters the pleural space from the site of pleural rupture, which acts as a one-way valve. Air is allowed to enter into the pleural space on inspiration but cannot escape as the rupture site closes on expiration. More air enters on inspiration and air pressure begins to exceed barometric pressure. Increasing air pressure pushes against the recoiled lung, causing compression atelectasis. Air also presses against the mediastinum, compressing and displacing the heart and great vessels. The air cannot escape, and the accumulating pressure causes the lung to collapse. As air continues to accumulate and intrapleural pressures rise, the mediastinum shifts away from the affected side and decreases venous return. This forces the heart, trachea, esophagus, and great vessels to the unaffected side, compressing the heart and the contralateral lung. Without immediate treatment, this emergency can rapidly become fatal. (See Understanding tension pneumothorax .)
|
UNDERSTANDING TENSION PNEUMOTHORAX
In tension pneumothorax, air accumulates intrapleurally and cannot escape. As intrapleural pressure rises, the ipsilateral lung is affected and also collapses. <center></center> |
Signs and symptoms
The following signs and symptoms may occur:
- sudden, sharp pleuritic pain exacerbated by chest movement, breathing, and coughing
- asymmetrical chest wall movement due to collapse of the lung
- shortness of breath due to hypoxia
- cyanosis due to hypoxia
- respiratory distress
- decreased vocal fremitus related to collapse of the lung
- absent breath sounds on the affected side due to collapse of the lung
- chest rigidity on the affected side due to decreased expansion
- tachycardia due to hypoxia
- crackling beneath the skin on palpation (subcutaneous emphysema), which is due to air leaking into the tissues.
Tension pneumothorax produces the most severe respiratory symptoms, including:
- decreased cardiac output
- hypotension due to decreased cardiac output
- compensatory tachycardia
- tachypnea due to hypoxia
- lung collapse due to air or blood in the intrapleural space
- mediastinal shift due to increasing tension
- tracheal deviation to the opposite side
- distended neck veins due to intrapleural pressure, mediastinal shift, and increased cardiovascular pressure
- pallor related to decreased cardiac output
- anxiety related to hypoxia
- weak and rapid pulse due to decreased cardiac output.
Complications
Possible complications include:
- decreased cardiac output
- hypoxemia
- cardiac arrest.
Diagnosis
The following tests help diagnose pneumothorax:
- Chest X-rays confirm the diagnosis by revealing air in the pleural space and, possibly, a mediastinal shift.
- Arterial blood gas analysis may reveal hypoxemia, possibly with respiratory acidosis and hypercapnia. Pa O 2 levels may decrease at first, but typically return to normal within 24 hours.
Treatment
Treatment depends on the type of pneumothorax.
Spontaneous pneumothorax with less than 30% of lung collapse, no signs of increased pleural pressure, and no dyspnea or indications of physiologic compromise, may be corrected with:
- bed rest to conserve energy and reduce oxygenation demands
- monitoring of blood pressure and pulse for early detection of physiologic compromise
- monitoring of respiratory rate to detect early signs of respiratory compromise
- oxygen administration to enhance oxygenation and improve hypoxia
- aspiration of air with a large-bore needle attached to a syringe to restore negative pressure within the pleural space.
Correction of pneumothorax with more than 30% of lung collapse may include:
- thoracostomy tube placed in the second or third intercostal space in the midclavicular line to try to re-expand the lung by restoring negative intrapleural pressure
- connection of the thoracostomy tube to underwater seal or to low-pressure suction to re-expand the lung
- if recurrent spontaneous pneumothorax, thoracotomy and pleurectomy may be performed, which causes the lung to adhere to the parietal pleura.
Open (traumatic) pneumothorax may be corrected with:
- chest tube drainage to re-expand the lung
- surgical repair of the lung.
Correction of tension pneumothorax typically involves:
- immediate treatment with large-bore needle insertion into the pleural space through the second intercostal space to re-expand the lung
- insertion of a thoracostomy tube if large amounts of air escape through the needle after insertion
- analgesics to promote comfort and encourage deep breathing and coughing.
Pulmonary edema
Pulmonary edema is an accumulation of fluid in the extravascular spaces of the lungs. It is a common complication of cardiac disorders and may occur as a chronic condition or may develop quickly and rapidly become fatal.
Causes
Pulmonary edema is caused by left-sided heart failure due to:
- arteriosclerosis
- cardiomyopathy
- hypertension
- valvular heart disease.
Factors that predispose the patient to pulmonary edema include:
- barbiturate or opiate poisoning
- cardiac failure
- infusion of excessive volume of intravenous fluids or overly rapid infusion
- impaired pulmonary lymphatic drainage (from Hodgkin's disease or obliterative lymphangitis after radiation)
- inhalation of irritating gases
- mitral stenosis and left atrial myxoma (which impairs left atrial emptying)
- pneumonia
- pulmonary venoocclusive disease.
Pathophysiology
Normally, pulmonary capillary hydrostatic pressure, capillary oncotic pressure, capillary permeability, and lymphatic drainage are in balance. When this balance changes, or the lymphatic drainage system is obstructed, fluid infiltrates into the lung and pulmonary edema results. If pulmonary capillary hydrostatic pressure increases, the compromised left ventricle requires increased filling pressures to maintain adequate cardiac output. These pressures are transmitted to the left atrium, pulmonary veins, and pulmonary capillary bed, forcing fluids and solutes from the intravascular compartment into the interstitium of the lungs. As the interstitium overloads with fluid, fluid floods the peripheral alveoli and impairs gas exchange.
If colloid osmotic pressure decreases, the hydrostatic force that regulates intravascular fluids (the natural pulling force) is lost because there is no opposition. Fluid flows freely into the interstitium and alveoli, impairing gas exchange and leading to pulmonary edema. (See Understanding pulmonary edema .)
A blockage of the lymph vessels can result from compression by edema or tumor fibrotic tissue, and by increased systemic venous pressure. Hydrostatic pressure in the large pulmonary veins rises, the pulmonary lymphatic system cannot drain correctly into the pulmonary veins, and excess fluid moves into the interstitial space. Pulmonary edema then results from the accumulation of fluid.
Capillary injury, such as occurs in adult respiratory distress syndrome or with inhalation of toxic gases, increases capillary permeability. The injury causes plasma proteins and water to leak out of the capillary and move into the interstitium, increasing the interstitial oncotic pressure, which is normally low. As interstitial oncotic pressure begins to equal capillary oncotic pressure, the water begins to move out of the capillary and into the lungs, resulting in pulmonary edema.
Signs and symptoms
Early signs and symptoms may include:
- dyspnea on exertion due to hypoxia
- paroxysmal nocturnal dyspnea due to decreased expansion of the lungs
- orthopnea due to decreased ability of the diaphragm to expand
- cough due to stimulation of cough reflex by excessive fluid
- mild tachypnea due to hypoxia
- increased blood pressure due to increased pulmonary pressures and decreased oxygenation
- dependent crackles as air moves through fluid in the lungs
- neck vein distention due to decreased cardiac output and increased pulmonary vascular resistance
- tachycardia due to hypoxia.
Later stages of pulmonary edema may include the following signs and symptoms:
- labored, rapid respiration due to hypoxia
- more diffuse crackles as air moves through fluid in the lungs
- cough, producing frothy, bloody sputum
- increased tachycardia due to hypoxemia
- arrhythmias due to hypoxic myocardium
- cold, clammy skin due to peripheral vasoconstriction
- diaphoresis due to decreased cardiac output and shock
- cyanosis due to hypoxia
- decreased blood pressure due to decreased cardiac output and shock
- thready pulse due to decreased cardiac output and shock.
Complications
Possible complications include:
- respiratory failure
- respiratory acidosis
- cardiac arrest.
Diagnosis
The following tests help diagnose pulmonary edema:
- Arterial blood gas analysis usually reveals hypoxia with variable Pa CO 2 , depending on the patient's degree of fatigue. Respiratory acidosis may occur.
- Chest X-rays show diffuse haziness of the lung fields and, usually, cardiomegaly and pleural effusion.
- Pulse oximetry may reveal decreasing Sa O 2 levels.
- Pulmonary artery catheterization identifies left-sided heart failure and helps rule out adult respiratory distress syndrome.
- Electrocardiography may show previous or current myocardial infarction.
|
UNDERSTANDING PULMONARY EDEMA
In pulmonary edema, diminished function of the left ventricle causes blood to back up into pulmonary veins and capillaries. The increasing capillary hydrostatic pressure pushes fluid into the interstitial spaces and alveoli. The following illustrations show a normal alveolus and an alveolus affected by pulmonary edema. <center></center> |
Treatment
Correcting this disorder typically involves:
- high concentrations of oxygen administered by nasal cannula to enhance gas exchange and improve oxygenation
- assisted ventilation to improve oxygen delivery to the tissues and promote acid-base balance
- diuretics, such as furosemide, ethacrynic acid, and bumetanide, to increase urination, which helps mobilize extravascular fluid
- positive inotropic agents, such as digoxin and amrinone, to enhance contractility in myocardial dysfunction
- pressor agents to enhance contractility and promote vasoconstriction in peripheral vessels
- antiarrhythmics for arrhythmias related to decreased cardiac output
- arterial vasodilators such as nitroprusside to decrease peripheral vascular resistance, preload, and afterload
- morphine to reduce anxiety and dyspnea, and to dilate the systemic venous bed, promoting blood flow from pulmonary circulation to the periphery.
Pulmonary hypertension
Pulmonary hypertension is indicated by a resting systolic pulmonary artery pressure (PAP) above 30 mm Hg and a mean PAP above 18 mm Hg. Primary or idiopathic pulmonary hypertension is characterized by increased PAP and increased pulmonary vascular resistance. This form is most common in women ages 20 to 40 and is usually fatal within 3 to 4 years.
| AGE ALERT Mortality is highest in pregnant women. |
Secondary pulmonary hypertension results from existing cardiac or pulmonary disease, or both. The prognosis in secondary pulmonary hypertension depends on the severity of the underlying disorder.
The patient may have no signs or symptoms of the disorder until lung damage becomes severe. In fact, it may not be diagnosed until an autopsy is performed.
Causes
Causes of primary pulmonary hypertension are unknown, but may include:
- hereditary factors
- altered immune mechanisms.
Secondary pulmonary hypertension results from hypoxemia as the result of the following.
Conditions causing alveolar hypoventilation:
- chronic obstructive pulmonary disease
- sarcoidosis
- diffuse interstitial pneumonia
- malignant metastases
- scleroderma
- obesity
- kyphoscoliosis.
Conditions causing vascular obstruction:
- pulmonary embolism
- vasculitis
- left atrial myxoma
- idiopathic venoocclusive disease
- fibrosing mediastinitis
- mediastinal neoplasm.
Conditions causing primary cardiac disease:
- patent ductus arteriosus
- atrial septal defect
- ventricular septal defect.
Conditions causing acquired cardiac disease:
- rheumatic valvular disease
- mitral stenosis.
Pathophysiology
In primary pulmonary hypertension, the smooth muscle in the pulmonary artery wall hypertrophies for no reason, narrowing the small pulmonary artery (arterioles) or obliterating it completely. Fibrous lesions also form around the vessels, impairing distensibility and increasing vascular resistance. Pressures in the left ventricle, which receives blood from the lungs, remain normal. However, the increased pressures generated in the lungs are transmitted to the right ventricle, which supplies the pulmonary artery. Eventually, the right ventricle fails (cor pulmonale). Although oxygenation is not severely affected initially, hypoxia and cyanosis eventually occur. Death results from cor pulmonale.
Alveolar hypoventilation can result from diseases caused by alveolar destruction or from disorders that prevent the chest wall from expanding sufficiently to allow air into the alveoli. The resulting decreased ventilation increases pulmonary vascular resistance. Hypoxemia resulting from this / mismatch also causes vasoconstriction, further increasing vascular resistance and resulting in pulmonary hypertension.
Coronary artery disease or mitral valvular disease causing increased left ventricular filling pressures may cause secondary pulmonary hypertension. Ventricular septal defect and patent ductus arteriosus cause secondary pulmonary hypertension by increasing blood flow through the pulmonary circulation via left-to-right shunting. Pulmonary emboli and chronic destruction of alveolar walls, as in emphysema, cause secondary pulmonary hypertension by obliterating or obstructing the pulmonary vascular bed. Secondary pulmonary hypertension can also occur by vasoconstriction of the vascular bed, such as through hypoxemia, acidosis, or both. Conditions resulting in vascular obstruction can also cause pulmonary hypertension because blood is not allowed to flow appropriately through the vessels.
Secondary pulmonary hypertension can be reversed if the disorder is resolved. If hypertension persists, hypertrophy occurs in the medial smooth muscle layer of the arterioles. The larger arteries stiffen and hypertension progresses. Pulmonary pressures begin to equal systemic blood pressure, causing right ventricular hypertrophy and eventually cor pulmonale.
Primary cardiac diseases may be congenital or acquired. Congenital defects cause a left-to-right shunt, re-routing blood through the lungs twice and causing pulmonary hypertension. Acquired cardiac diseases, such as rheumatic valvular disease and mitral stenosis, result in left ventricular failure that diminishes the flow of oxygenated blood from the lungs. This increases pulmonary vascular resistance and right ventricular pressure.
Signs and symptoms
The following signs and symptoms may occur:
- increasing dyspnea on exertion from left ventricular failure
- fatigue and weakness from diminished oxygenation to the tissues
- syncope due to diminished oxygenation to brain cells
- difficulty breathing due to left ventricular failure
- shortness of breath due to left ventricular failure
- pain with breathing due to lactic acidosis buildup in the tissues
- ascites due to right ventricular failure
- neck vein distention due to right ventricular failure
- restlessness and agitation due to hypoxia
- decreased level of consciousness, confusion, and memory loss due to hypoxia
- decreased diaphragmatic excursion and respiration due to hypoventilation
- possible displacement of point of maximal impulse beyond the midclavicular line due to fluid accumulation
- peripheral edema due to right ventricular failure
- easily palpable right ventricular lift due to altered cardiac output and pulmonary hypertension
- reduced carotid pulse
- palpable and tender liver due to pulmonary hypertension
- tachycardia due to hypoxia
- systolic ejection murmur due to pulmonary hypertension and altered cardiac output
- split S 2 , S 3 , and S 4 sounds due to pulmonary hypertension and altered cardiac output
- decreased breath sounds due to fluid accumulation in the lungs
- loud, tubular breath sounds due to fluid accumulation in the lungs.
Complications
Possible complications of pulmonary hypertension include:
- cor pulmonale
- cardiac failure
- cardiac arrest.
Diagnosis
The following tests help diagnose pulmonary hypertension:
- Arterial blood gas analysis reveals hypoxemia.
- Electrocardiography in right ventricular hypertrophy shows right axis deviation and tall or peaked P waves in inferior leads.
- Cardiac catheterization reveals increased PAP, with systolic pressure above 30 mm Hg. It may also show an increased pulmonary capillary wedge pressure (PCWP) if the underlying cause is left atrial myxoma, mitral stenosis, or left ventricular failure; otherwise, PCWP is normal.
- Pulmonary angiography detects filling defects in pulmonary vasculature, such as those that develop with pulmonary emboli.
- Pulmonary function studies may show decreased flow rates and increased residual volume in underlying obstructive disease; in underlying restrictive disease, they may show reduced total lung capacity.
- Radionuclide imaging detects abnormalities in right and left ventricular functioning.
- Open lung biopsy may determine the type of disorder.
- Echocardiography allows the assessment of ventricular wall motion and possible valvular dysfunction. It can also demonstrate right ventricular enlargement, abnormal septal configuration consistent with right ventricular pressure overload, and reduction in left ventricular cavity size.
- Perfusion lung scanning may produce normal or abnormal results, with multiple patchy and diffuse filling defects that don't suggest pulmonary embolism.
Treatment
Managing this disorder typically involves:
- oxygen therapy to correct hypoxemia and resulting increased pulmonary vascular resistance
- fluid restriction in right ventricular failure to decrease workload of the heart
- digoxin to increase cardiac output
- diuretics to decrease intravascular volume and extravascular fluid accumulation
- vasodilators to reduce myocardial workload and oxygen consumption
- calcium channel blockers to reduce myocardial workload and oxygen consumption
- bronchodilators to relax smooth muscles and increase airway patency
- beta-adrenergic blockers to improve oxygenation
- treatment of the underlying cause to correct pulmonary edema
- heart-lung transplant in severe cases.
Respiratory failure
When the lungs can't adequately maintain arterial oxygenation or eliminate carbon dioxide, acute respiratory failure results, which can lead to tissue hypoxia. In patients with normal lung tissue, respiratory failure is indicated by a Pa CO 2 above 50 mm Hg and a Pa O 2 below 50 mm Hg. These levels do not apply to patients with chronic obstructive pulmonary disease (COPD), who have a consistently high Pa CO 2 (hypercapnia) and a low Pa O 2 (hypoxemia). Acute deterioration in arterial blood gas values for these patients and corresponding clinical deterioration signify acute respiratory failure.
Causes
Conditions that can result in alveolar hypoventilation, / mismatch, or right-to-left shunting can lead to respiratory failure; these include:
- COPD
- bronchitis
- pneumonia
- bronchospasm
- ventilatory failure
- pneumothorax
- atelectasis
- cor pulmonale
- pulmonary edema
- pulmonary emboli
- central nervous system disease
- central nervous system trauma
- central nervous system depressant drugs, such as anesthetics, sedation, and hypnotics
- neuromuscular diseases, such as poliomyelitis or amyotrophic lateral sclerosis.
Pathophysiology
Respiratory failure results from impaired gas exchange. Any condition associated with alveolar hypoventilation, / mismatch, and intrapulmonary (right-to-left) shunting can cause acute respiratory failure if left untreated.
Decreased oxygen saturation may result from alveolar hypoventilation, in which chronic airway obstruction reduces alveolar minute ventilation. Pa O 2 levels fall and Pa CO 2 levels rise, resulting in hypoxemia.
Hypoventilation can occur from a decrease in the rate or duration of inspiratory signal from the respiratory center, such as with central nervous system conditions or trauma or central nervous system depressant drugs. Neuromuscular diseases, such as poliomyelitis or amytrophic lateral sclerosis, can result in alveolar hypoventilation if the condition affects normal contraction of the respiratory muscles. The most common cause of alveolar hypoventilation is airway obstruction, often seen with COPD (emphysema or bronchitis).
The most common cause of hypoxemia ― V/Q imbalance ― occurs when conditions such as pulmonary embolism or adult respiratory distress syndrome interrupt normal gas exchange in a specific lung region. Too little ventilation with normal blood flow or too little blood flow with normal ventilation may cause the imbalance, resulting in decreased Pa O 2 levels and, thus, hypoxemia.
Decreased Fi O 2 is also a cause of respiratory failure, although it is uncommon. Hypoxemia results from inspired air that does not contain adequate oxygen to establish an adequate gradient for diffusion into the blood ― for example, at high altitudes or in confined, enclosed spaces.
The hypoxemia and hypercapnia characteristic of respiratory failure stimulate strong compensatory responses by all of the body systems, including the respiratory, cardiovascular, and central nervous systems. In response to hypoxemia, for example, the sympathetic nervous system triggers vasoconstriction, increases peripheral resistance, and increases the heart rate. Untreated / imbalances can lead to right-to-left shunting in which blood passes from the heart's right side to its left without being oxygenated.
Tissue hypoxemia occurs, resulting in anaerobic metabolism and lactic acidosis. Respiratory acidosis occurs from hypercapnia. Heart rate increases, stroke volume increases, and heart failure may occur. Cyanosis occurs due to increased amounts of unoxygenated blood. Hypoxia of the kidneys results in release of erythropoietin from renal cells, which causes the bone marrow to increase production of red blood cells ― an attempt by the body to increase the blood's oxygen-carrying capacity.
The body responds to hypercapnia with cerebral depression, hypotension, circulatory failure, and an increased heart rate and cardiac output. Hypoxemia or hypercapnia (or both) causes the brain's respiratory control center first to increase respiratory depth (tidal volume) and then to increase the respiratory rate. As respiratory failure worsens, intercostal, supraclavicular, and suprasternal retractions may also occur.
Signs and symptoms
The following signs and symptoms may occur:
- cyanosis of oral mucosa, lips, and nail beds due to hypoxemia
- nasal flaring due to hypoxia
- ashen skin due to vasoconstriction
- use of accessory muscles for respiration
- restlessness, anxiety, agitation, and confusion due to hypoxic brain cells and alteration in level of consciousness
- tachypnea due to hypoxia
- cold, clammy skin due to vasoconstriction
- dull or flat sound on percussion if the patient has atelectasis or pneumonia
- diminished breath sounds over areas of hypoventilation.
Complications
Possible complications include:
- tissue hypoxia
- metabolic acidosis
- cardiac arrest.
Diagnosis
- Arterial blood gas analysis indicates respiratory failure by deteriorating values and a pH below 7.35. Patients with COPD may have a lower than normal pH compared with their previous levels.
- Chest X-rays identify pulmonary diseases or conditions, such as emphysema, atelectasis, lesions, pneumothorax, infiltrates, and effusions.
- Electrocardiography can demonstrate arrhythmias; these are commonly found with cor pulmonale and myocardial hypoxia.
- Pulse oximetry reveals a decreasing Sa O 2 .
- White blood cell count detects underlying infection.
- Abnormally low hemoglobin and hematocrit levels signal blood loss, which indicates decreased oxygen-carrying capacity.
- Hypokalemia may result from compensatory hyperventilation, the body's attempt to correct acidosis.
- Hypochloremia usually occurs in metabolic alkalosis.
- Blood cultures may identify pathogens.
- Pulmonary artery catheterization helps to distinguish pulmonary and cardiovascular causes of acute respiratory failure and monitors hemodynamic pressures.
Treatment
Correcting this disorder typically involves:
- oxygen therapy to promote oxygenation and raise Pa O 2
- mechanical ventilation with an endotracheal or a tracheostomy tube if needed to provide adequate oxygenation and to reverse acidosis
- high-frequency ventilation, if patient doesn't respond to treatment, to force the airways open, promoting oxygenation and preventing collapse of alveoli
- antibiotics to treat infection
- bronchodilators to maintain patency of the airways
- corticosteroids to decrease inflammation
- fluid restrictions in cor pulmonale to reduce volume and cardiac workload
- positive inotropic agents to increase cardiac output
- vasopressors to maintain blood pressure
- diuretics to reduce edema and fluid overload
- deep breathing with pursed lips if patient is not intubated and mechanically ventilated to help keep airway patent
- incentive spirometry to increase lung volume.
Sudden infant death syndrome
Sudden infant death syndrome (SIDS) is the leading cause of death among apparently healthy infants, ages 1 month to 1 year. Also called crib death, it occurs at a rate of 2 in every 1,000 live births; about 7,000 infants die of SIDS in the United States each year. The peak incidence occurs between ages 2 and 4 months.
| CULTURAL DIVERSITY The incidence of SIDS is slightly higher in preterm infants, Inuit infants, disadvantaged black infants, infants of mothers younger than age 20, and infants of multiple births. The incidence is also 10 times higher in SIDS siblings and in infants of mothers who are drug addicts. |
Causes
Common causes of SIDS include:
- hypoxemia, possibly due to apnea or immature respiratory system
- re-breathing of carbon dioxide, as occurs when infant is face down on the mattress.
Pathophysiology
It has been suggested that the infant with SIDS may have damage to the respiratory control center in the brain from chronic hypoxemia. The infant may also have periods of sleep apnea and eventually dies during an episode.
Normally, increased carbon dioxide levels stimulate the respiratory center to initiate breathing until very high levels actually depress the ventilatory effort. In infants who experience SIDS or near-miss episodes of SIDS, the child may not respond to increasing carbon dioxide levels, showing only depressed ventilation. In these infants, an episode of apnea may occur and carbon dioxide levels increase; however, the child is not stimulated to breathe. Apnea continues until very high levels of carbon dioxide completely suppress the ventilatory effort and the child ceases to breathe.
Signs and symptoms
The following signs and symptoms may occur:
- history indicating that the infant was found not breathing
- mottling of the skin due to cyanosis
- apnea and absence of pulse due to severe hypoxemia.
Complications
Possible complications include:
- death
- brain damage from near-miss episodes.
Diagnosis
Autopsy is performed to rule out other causes of death.
Treatment
Treatment measures associated with SIDS typically involve:
- resuscitation to restore circulation and oxygenation (usually futile)
- emotional support to the family
- prevention of SIDS in high-risk infants or those who have had near-miss episodes.
| AGE ALERT Infants at risk for SIDS should be monitored at home on an apnea monitor until the age of vulnerability has passed. Also, parents should be educated in prompt emergency treatment of detected apnea. |
