Approach to the Management of the Patient with Acute Respiratory Distress Syndrome
Chronic Obstructive Pulmonary Disease
Approach to the Patient With Cough
Approach to the Patient with Dyspnea
Idiopathic Pulmonary Fibrosis
Obstructive Sleep Apnea
Approach to the Patient with Pleural Disease
Approach to the Patient with a Solitary Pulmonary Nodule
Approach to the Patient with Suspected Pneumonia
APPROACH TO THE MANAGEMENT OF THE PATIENT WITH ACUTE RESPIRATORY DISTRESS SYNDROME
DEFINITION AND ETIOLOGY
Acute respiratory distress syndrome (ARDS, previously called adult respiratory distress syndrome) represents the abrupt onset of diffuse lung injury characterized by severe hypoxemia and generalized pulmonary infiltrates in the absence of cardiac failure. It has most often been associated with sepsis syndrome and bacterial or viral pneumonia. Other causes include major traumatic injury, aspiration of gastric contents, massive transfusion, inhalation injury, pancreatitis, near-drowning, fat embolism after long bone fractures, and drug overdose.
Structural changes: Inflammatory cells, especially neutrophils, accumulate within the alveolar space and are believed to contribute to lung injury by releasing granular enzymes and oxidants. Type I alveolar epithelial cells undergo cytopathic changes, and the alveolar basement membrane is damaged. Changes in cellular permeability allow interstitial and alveolar edema; hyaline membranes are then produced by aggregation of fibrin and other proteins in the alveolar space. As the process continues, intravascular thrombosis, loss of pulmonary microvasculature, and fibrotic distortion of septal architecture occur.
Physiologic changes: ARDS is associated with impaired gas exchange, altered lung mechanics, and pulmonary vascular changes. Lung compliance and functional residual capacity decrease, and work of breathing increases. The loss of microvasculature in the later stages leads to pulmonary hypertension.
CLINICAL PRESENTATION AND DIAGNOSIS
ARDS develops rapidly, usually within 12 to 72 hours of the predisposing event. Respiratory distress, severe hypoxemia, and generalized pulmonary infiltrates all are necessary for the diagnosis. The most widely accepted definition of hypoxemia in this setting is a ratio of the arterial oxygen tension (PaO2) to the fraction of inspired oxygen (FIO2) less than 200. Congestive heart failure as an alternative diagnosis can be excluded either clinically or by determining that the pulmonary artery occlusion pressure is less than 18 mm Hg. To date, no specific laboratory findings have been described.
PROGNOSIS AND MANAGEMENT
Therapy is primarily supportive. Well-controlled studies have failed to find a benefit for glucocorticoids in the management or prevention of ARDS. The selective pulmonary vasodilator nitric oxide has been shown to improve oxygenation and to reduce pulmonary artery pressures without affecting mortality. Mechanical ventilation is almost always needed, as is positive end-expiratory pressure (PEEP). The assist-control (A/C) ventilator mode is preferred by most experts. Lower ventilator tidal volumes (6 mL per kilogram rather than 10 to 15 mL per kilogram) have been proved to decrease ventilator-associated lung injury, such as barotrauma-induced pneumothorax, and to reduce mortality. Survival rates in the most recent studies have been 60% to 70%. The course is variable, lasting from a few days to several weeks. The average duration of mechanical ventilation is approximately 10 to 12 days. One-third of the deaths of patients with ARDS are related to the underlying disease or injury.
DEFINITION, EPIDEMIOLOGY, AND ETIOLOGY
Asthma is defined as intermittent, reversible airway obstruction in association with increased nonspecific bronchial reactivity and airway inflammation. It is one of the most common and expensive chronic illnesses in the United States, affecting 5% to 10% of the population. The incidence follows a bimodal age distribution, with an early peak from 4 to 10 years of age and second peak after 40 years of age. African American and Hispanic populations, particularly those in inner city areas, have both higher incidences and higher mortality rates than other groups. The basis for asthma is poorly understood. Multifactorial genetic factors likely contribute to susceptibility, but environmental exposures also are important. Among children, potential triggers include maternal cigarette smoking, infection with respiratory syncytial virus, and exposure to indoor allergens such as house dust mites, cockroaches, cats, and molds. Among adults, occupational asthma is prevalent in the lumber, plastics, and paint industries and among hospital workers with a sensitivity to latex.
For asthma to develop, a complex immunologic reaction involving inflammatory cells and cytokines must be initiated and maintained. Although many cell types may be involved, lymphocytes, eosinophils, and mast cells predominate. Tissue damage involves the epithelium and the submucosal space, and hyperplasia of the airway smooth muscle occurs. Reversible airflow limitation is present, demonstrated by a reduction in the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) (less than 75% among adults) and an improvement in the FEV1 ‘more than 12% to 15% after inhalation of a b-agonist. Other physiologic changes include hyperinflation (increased residual volume) and increased airway resistance. Airway hyperresponsiveness is demonstrated by methacholine, histamine, or exercise testing. A positive result of a methacholine challenge is defined as a reduction in FEV1 of 20% or more with 8 mg per milliliter or less of methacholine. However, other diseases can be associated with airway hyperresponsiveness, such as chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), bronchiectasis, and seasonal allergic rhinitis.
CLINICAL FINDINGS AND DIAGNOSIS
The symptoms of asthma include cough, wheezing, chest tightness, and dyspnea. The diagnosis should be made through documentation of reversible airway obstruction (see earlier) in the setting of symptoms of the disease. Because of the intermittent nature of the disease, however, an occasional patient may have normal spirometric findings. If the history suggests asthma, the patient’s peak flow can be monitored at home. Variation in peak flows more than 10% generally is considered diagnostic of asthma. If this sign is not present and the patient still has symptoms, a methacholine challenge may be performed (see earlier). The methacholine challenge is particularly helpful in the evaluation of patients with cough variant asthma, who often have normal spirograms and no symptoms other than cough.
Differentiation of COPD from asthma among cigarette smokers can be difficult. COPD usually decreases diffusion capacity, which does not occur in asthma. Vocal cord dysfunction involves involuntary closure of the vocal cords, usually during inspiration but occasionally during expiration as well. The diagnosis is made through laryngoscopic visualization of inappropriate closure of the cords during inspiration or flattening of the inspiratory limb of a flow-volume loop. Upper airway obstruction due to tumors or strictures causes flattening in both the inspiratory and expiratory phases of the flow-volume loops. CHF can cause wheezing known as cardiac asthma.
A thorough history should be obtained to determine possible triggers such as exposure to allergens, use of nonsteroidal anti-inflammatory drugs, and occupational exposure to antigens. If indoor allergens are suspected, allergy skin testing should be undertaken to guide avoidance therapy. Exacerbating factors such as sinus disease, gastroesophageal reflux, and stressful life situations should be sought. Table 363.1 outlines the current definitions for asthma severity. Table 363.2 presents the appropriate treatments for each level.
Chronic maintenance therapy: In general, inhalation of glucocorticoids is the cornerstone of the management of all but the most mild asthma. These agents are effective and safe and counter the underlying inflammatory basis of the disease. The side effect of oral thrush can be minimized with the use of a spacer device or by rinsing the mouth after use. Fluticasone, budesonide, and beclomethasone are likely more potent than flunisolide or triamcinolone. Cromones such as nedocromil and cromolyn sodium are considered second-line agents for long-term control among adults. Little is known about the mechanism of action. Although these agents do have mast cell–stabilizing properties, the clinical importance of this effect is unclear.
Theophyllines are nonspecific phosphodiestrase inhibitors with weak bronchodilating effects and some antiinflammatory properties. They are classified as second-line agents for long-term control among patients with mild or moderate persistent asthma. Disadvantages include numerous drug–drug interactions and a narrow therapeutic window that can lead to seizures and arrhythmias with higher serum drug levels. Long-acting inhaled b-agonists include salmeterol and formoterol. These agents provide effective bronchodilation for more than 12 hours and have been shown to prevent nocturnal symptoms and diurnal peak flow fluctuations. They are primarily recommended for use with inhaled glucocorticoids in moderate persistent asthma. Because the pharmacokinetic properties make these drugs poor therapy for acute exacerbations, patients should always have a short-acting inhaled b-agonist to use for acute symptoms.
Leukotriene modulators (zafirlukast, montelukast, zileuton) diminish the production of leukotrienes and have shown efficacy in control of asthma induced by allergens, exercise, or aspirin. The most recent guidelines suggest that these drugs be used to manage mild, persistent asthma as alternatives to inhaled glucocorticoids, theophylline, and cromones.
Quick relief medications: Patients may need quick relief if symptoms worsen acutely. However, because patients’ perceptions of airflow limitation do not correlate well with the actual degree of obstruction, home peak flow monitoring should be used to guide therapy. More than a 20% decrease in peak flow should be an indication for attention and treatment by the patient, whereas a 50% decline from baseline always necessitates an aggressive approach by the treating physician. All patients should have an action plan to begin treatment at home. This can include increased use of short-acting inhaled b-agonists, such as albuterol, and initial oral glucocorticoid therapy if there is insufficient response to the b-agonists. Although systemic glucocorticoids are the most effective asthma medications, toxicity necessitates that ongoing use be as limited as possible. The initial daily dose of prednisone for patients with an acute, severe exacerbation is 60 to 120 mg. The dose can be tapered gradually on the basis of clinical response.
CHRONIC OBSTRUCTIVE PULMONARY DISEASE
Chronic obstructive pulmonary disease (COPD) is a group of disorders that have in common the presence of persistent airflow obstruction. Chronic bronchitis is characterized clinically by chronic cough and sputum production for at least 3 months for 2 successive years without other known causes. Emphysema is a condition with abnormal permanent enlargement of airspaces distal to the terminal bronchioles accompanied by nonfibrotic destruction of walls. Asthma is characterized by reversible airway narrowing and increased responsiveness to various stimuli. Many patients have features of more than one of these diseases and are given the less specific diagnosis COPD.
INCIDENCE AND EPIDEMIOLOGY
The overall prevalence in the United States is 4% to 6% among men and 1% to 3% among women. COPD is recognized among 10% to 15% of adults older than 55 years. As of 1990, COPD was the fourth leading cause of death in the United States and accounted for more than 13% of all hospitalizations.
ETIOLOGY AND PATHOGENESIS
Cigarette smoking is the most important risk factor and accounts for nearly 90% of all cases of COPD. Current smokers have 10 times the relative risk of nonsmokers. There is, however, marked individual variation in susceptibility; only 10% to 15% of smokers experience COPD. It has not been clearly established that passive smoke exposure causes COPD. The mechanisms by which smoking leads to COPD are not well understood. In the case of emphysema, the disease seems to be caused by an imbalance between lung proteases and antiproteases that leads to increased lung destruction. An inherited deficiency of a1 protease inhibitor is associated with premature emphysema. In chronic bronchitis, pathologic changes in the airways include an inflammatory cell response, goblet cell proliferation, and an increase in smooth muscle.
COPD typically manifests later in life. The insidious development of dyspnea is the hallmark symptom. A cough is frequent and often is attributed to smoker’s cough early in disease. The cough usually is productive of mucoid sputum. There may be a history of frequent respiratory infections. Some patients with COPD have abnormal gas exchange with hypoxemia or hypercapnea. Hypoxemia may be associated with cognitive or personality changes, polycythemia, and cyanosis. Chronic hypercapnea may cause headache.
During the physical examination, it is important to assess maximum expiratory flow for persons at high risk. This can be assessed easily with forced expiratory time (FET). Healthy persons can exhale completely within 4 seconds. An FET longer than 6 seconds signifies substantial obstruction. Other physical signs develop only when the disease is moderate to severe. Overinflation of the lungs can increase the anteroposterior diameter of the thorax, lower and flatten the diaphragm, and reduce respiratory excursion. The accessory breathing muscles (neck and intercostals) contribute more to ventilation. Wheezing with tidal respirations may be evident. With advanced emphysema, the breath sounds are diminished because of a reduction in flow and an increase in lung inflation. Signs of pulmonary hypertension and right-sided heart failure, such as peripheral edema and hepatic congestion, usually represent advanced disease.
LABORATORY STUDIES AND DIAGNOSTIC TESTS
Pulmonary function tests: The central diagnostic feature is reduced expiratory airflow due to airway narrowing. Spirometry is the standard test and is useful for detecting obstruction, staging severity, and following the disease course. A reduction in forced expiratory volume in 1 second (FEV1) in relation to the forced vital capacity (FVC)—the FEV1/FVC ratio—is the standard indicator of obstruction. The FEV1 is the best measure of severity; it correlates with exercise tolerance and survival. Measurements of lung volume reveal increased residual volume, functional residual capacity, and sometimes total lung capacity (TLC). Emphysema causes a greater increase in TLC than do other lung diseases and reduces carbon monoxide diffusing capacity because of the loss of alveolar–capillary surface area.
Radiologic studies: Chest radiography has limited usefulness in diagnosing or staging COPD. The main use of this modality is in detecting other parenchymal lung or cardiovascular diseases that manifest with similar symptoms. With advanced emphysema a chest radiograph may reveal hyperinflation of the lungs with a low, flat diaphragm and an increase in the retrosternal airspace on the lateral projection. The emphysematous lungs may appear radiolucent because of bullous changes. High-resolution computed tomography may document evidence of emphysema.
Arterial blood gas analysis: The analysis may reveal hypoxemia, particularly with exercise, and hypercapnea, particularly in advanced disease. The relation between gas exchange abnormalities and other measures of lung function is poor. Two characteristic patterns of disease can be defined with blood gas findings. Patients with severe dyspnea, mild hypoxemia, and normal-to-low arterial PCO2 have been called pink puffers (type A COPD), reflecting their color and increased breathing effort. Patients with severe hypoxemia, carbon dioxide retention, right-sided heart failure, but little dyspnea are called blue bloaters (type B COPD), reflecting their bloated, cyanotic appearance and low ventilation. These differences may reflect variations in ventilation–perfusion (
) mismatching and central respiratory drive. Most patients, however, fall between these two extremes.
Prevention: Primary and secondary prevention strategies include avoidance or discontinuation of cigarette smoking and a1 protease inhibitor replacement for persons with both proven genetic deficiency and abnormal lung function. Tertiary prevention to reduce complications of symptomatic disease include smoking cessation, influenza and pneumococal vaccination, and pulmonary rehabilitation.
Oxygen therapy: Oxygen is the only therapy proven to prolong survival. Studies have justified the long-term use of oxygen therapy for severe resting hypoxemia (arterial Po2 55 mm Hg or less). For patients with an arterial Po2 between 56 and 59 mm Hg, oxygen therapy is indicated if erythrocytosis (hematocrit 55% or more) or cor pulmonale is present. The decision for long-term therapy should be made only when the patient has been in stable condition with optimal therapy for at least 30 days.
Symptomatic treatment: Medical treatment is directed at the reversible component of airway obstruction and control of secretions. Bronchodilators used to improve symptoms and increase airway caliber include b2-agonists, anticholinergics, and methylxanthines such as theophylline. b2-Agonists are best administered by means of inhalation with an emphasis on proper technique. The most common side effects are tremor and tachycardia. Anticholinergics such as ipratropium bromide have recently gained prominence in the management of COPD. They, too, are best administered by means of inhalation. Oral theophylline improves bronchial tone, diaphragmatic function, respiratory drive, and mucociliary clearance. The target therapeutic level is typically 10 to 20 µg per milliliter. Side effects occur even within this range; they include tremor, insomnia, irritability, and gastrointestinal upset. More serious side effects, including vomiting, arrhythmias, hypotension, and seizures, generally develop at higher blood levels.
Glucocorticoids can be beneficial to some patients with stable symptoms. A limited trial is probably justified for patients who cannot be treated with standard bronchodilators alone. Treatment should be continued only for, the minority who have marked improvement in pulmonary function. Inhaled steroids are safer, but their effectiveness has not been as well established. Oral or intravenous steroids are clearly indicated for patients experiencing acute flare-ups of COPD.
Control of secretions is important for patients with a chronic productive cough. These patients should be encouraged to drink several glasses of fluid each day, but excessive hydration is not warranted. The patients also should be taught the technique of controlled coughing, which involves deep inspiration, breath-holding for a few seconds, and then coughing two or three times. The use of mucolytic agents (iodinated glycerol, nebulized acetylcysteine, or recombinant DNase) to thin secretions and promote clearance is controversial. Because cough is an essential protective mechanism, cough suppression therapy is not recommended. For acute exacerbations, when sputum changes color and increases in volume, treatment with antibiotics for 7 to 10 days is indicated. Oral antibiotics such as trimethoprim–sulfamethoxazole, amoxicillin, amoxicillin–clavulanate, tetracycline, or erythromycin are commonly chosen to cover pathogens colonizing the respiratory tract, including Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis.
APPROACH TO THE PATIENT WITH COUGH
EPIDEMIOLOGY AND PATHOPHYSIOLOGY
Coughing is the fifth most common symptom among patients at outpatient clinics in the United States. The cough reflex is subserved by vagal afferent pathways arising from the trachea, intrapulmonary airways, and larynx. Although it is an important natural defense mechanism, excessive coughing generates considerable intrathoracic pressure and may be associated with complications such as pneumothorax, syncope, subconjunctival hemorrhage, cervical disc prolapse, urinary incontinence, and esophageal perforation.
The differential diagnosis is extensive (Table 352.2). Acute cough usually is caused by viral or bacterial upper respiratory infection. It also, however, can be a manifestation of more serious conditions such as acute bacterial pneumonia, congestive heart failure, pulmonary embolism, asthma, or aspiration. These conditions usually are accompanied by other symptoms, such as dyspnea or fever. Chronic cough (cough that persists for more than 1 month) is most commonly caused by asthma, gastroesophageal reflux (GER), postnasal drip, chronic bronchitis, or bronchiectasis. Smoking is also a common cause of coughing.
The best approach is to exclude first the most common conditions associated with chronic dry coughing—postnasal drip, asthma, and GER. Often the history and physical examination are sufficient to suggest one of these diagnoses, and a therapeutic trial can then be undertaken. If further diagnostic evaluation for these conditions is necessary, the tests performed should be based on the initial suspicion, as follows: for possible postnasal drip, allergy tests and sinus computed tomography (CT); for suspected asthma, peak expiratory flow measurements at home and a bronchoprovocation test with histamine or methacholine; and for possible GER, 24-hour pH monitoring and perhaps endoscopic examination of the esophagus. A chest radiograph is recommended for most patients, unless a cause is quickly apparent and the cough improves with therapy. If the diagnosis remains elusive, studies such as full pulmonary function tests, lung CT, and fiberoptic bronchoscopy should be considered.
Specific therapies: Many of the causes of chronic cough have specific therapies. The most straightforward is discontinuation of an offending medication, such as an angiotensin-converting enzyme (ACE) inhibitor, although it may take weeks for the cough to resolve. Postnasal drip is managed with glucocorticoid nasal sprays and an antihistamine with or without a short course of nasal decongestants; an antibiotic is used if purulent sinusitis is suspected. GER is managed with histamine 2 blockers or proton pump inhibitors, asthma with bronchodilators and inhaled glucocorticoids.
Nonspecific therapy: Opiates such as codeine are the most effective antitussive agents, but they cause physical dependence, respiratory depression, nausea and vomiting, and constipation. Non-narcotic antitussives include dextromethorphan, a synthetic morphine derivative with no analgesic or sedative properties. It is a constituent of many nonprescription cough remedies. Mucolytic agents such as acetylcysteine often are used to facilitate expectoration by reducing sputum viscosity in patients with chronic bronchitis, but there is little evidence that these agents are beneficial. Local anesthetics such as aerosolized lidocaine should be reserved for cases of severe, intractable cough, because they remove reflexes that protect the lungs from noxious substances.
EPIDEMIOLOGY AND PATHOPHYSIOLOGY
Cystic fibrosis (CF) is an autosomal recessive disorder; it affects 1 in 3,000 U.S. whites, 1 in 15,000 African Americans, and 1 in 90,000 Asian Americans. The CF gene encodes for the CF transmembrane conductance regulator (CFTR). In CF, one of the chloride ion channels of epithelial cells is either absent or dysfunctional. This leads to decreased water content and increased viscosity of various secretions, including those in the lung and the pancreas. In addition, the high sodium concentrations in airway secretions may inactivate the antimicrobial peptides secreted by airway epithelial cells.
Pulmonary and sinus disease: Symptoms generally begin in childhood. A self-perpetuating destructive inflammatory reaction is manifested by bronchitis, bronchiolitis, bronchiectasis, and a progressive decline in pulmonary function. Infection is predominantly caused by Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa organisms. P. aeruginosa eventually becomes the dominant organism in more than 90% of patients; a mucoid strain eventually replaces other pathogens. Acute exacerbations consist of increased coughing, sputum production, and dyspnea. Hemoptysis and pneumothorax are complications of more advanced disease. Clubbing of the fingers and toes is a universal finding. Mechanical obstruction of the sinus ostia by viscous mucus can occur and is followed by bacterial infection. Nasal polyposis is common.
Pancreatic and gastrointestinal disease: Most patients have exocrine pancreatic insufficiency and malabsorption; acute pancreatitis occurs in 10% of cases. Diabetes mellitus occurs among 15% of patients. It is slow in onset and nonketotic. Episodes of complete or partial intestinal obstruction occur among 10% to 20% of adult patients. Other gastrointestinal complications include gastroesophageal reflux, peptic ulceration, Crohn’s disease, cholelithiasis, and elevated levels of liver enzymes.
Other complications: Men with CF have obstructive azoospermia and are infertile. Women have normal fertility. Nondestructive, episodic arthritis, most commonly involving the lower limbs and fingers, occurs among some patients. Patients are susceptible to osteopenia and osteoporosis.
The diagnosis is based on a positive result of a sweat chloride test (more than 60 mEq per liter) or results of genetic tests that demonstrate two CF alleles and symptoms compatible with CF. The sweat test is highly sensitive (96% in adults) and specific for CF, although false-positive results can occur if the patient has hypoadrenalism, hypothyroidism, or nephrogenic diabetes insipidus. Chest radiographs first show overinflation, peribronchial cuffing, and small infiltrates and then show bronchiectasis and diffuse fibrosis, which is most marked in the upper lobes. Almost all patients have panopacification of the paranasal sinuses. Malabsorption is characterized by elevated fecal fat levels and decreased serum levels of fat-soluble vitamins.
PROGNOSIS AND MANAGEMENT
In the United States in 1997, the median survival period was 30.6 years. Prognostic factors include genotype, pulmonary function, results of chest radiographs, and nutritional status. The forced expiratory volume in 1 second (FEV1) is the single most sensitive predictor of mortality. An FEV1 less than 30% of predictive is associated with a 45% 2-year mortality risk. About 95% of patients die of pulmonary complications.
Pulmonary and sinus disease: The mainstays of treatment are chest physical therapy and antibiotics, although the bacterial pathogens rarely are eradicated. For exacerbations, intervenous antibiotics are usually given for 2 weeks. The use of prophylactic antibiotics, including aerosolized forms, is controversial. Inhaled bronchodilators such as b2-agonists and ipratropium bromide are indicated for those who respond. Recombinant human DNase alters the rheologic qualities of the sputum by cutting the size of DNA molecules. Oral glucocorticoids slow the decline in pulmonary function but cause serious side effects. Inhalation of steroids has been less well studied but seems reasonable in the care of patients with an asthmatic component to the disease. Oxygen therapy is given to patients with hypoxemia. A final therapeutic option for a few patients is lung transplantation. Sinus disease is managed with antibiotics, nasal irrigation, nasal steroids, and, if necessary, surgical drainage.
Pancreatic and gastrointestinal disease: Malabsorption is managed with oral pancreatic enzymes. Diabetes necessitates dietary control and insulin; the use of oral hypoglycemic agents is controversial. Intestinal obstruction is treated with rehydration, nasogastric suction, and hyperosmolar enemas. Surgery rarely is needed.
Nutritional management: Nutritional deficiencies are caused by malabsorption, decreases in food intake, and an increase in metabolic requirements due to the disease. Malabsorption must be controlled. Most patients need vitamin A and E supplementation. Enteral feedings should be offered to patients who lose weight despite aggressive dietary measures.
Genetic counseling: Patients and their relatives should be offered nondirective counseling concerning carrier testing and the risks of having a CF-affected child. Gene therapy: CFTR vectors have been given to CF patients, either to the nose or lungs or both. The efficacy and safety of this intervention are under study.
APPROACH TO THE PATIENT WITH DYSPNEA
DEFINITIONS AND PATHOPHYSIOLOGY
The term dyspnea is used to describe a variety of perceptions of difficulty or distress relating to breathing. Several factors may be identified that help determine whether a given pathophysiologic condition is associated with dyspnea. There may be an increased ventilatory requirement or a reduced ventilatory capacity. Even if ventilatory requirements are within a person’s capacity, the ventilatory effort may be increased by such factors as abnormal lung mechanics or respiratory muscle fatigue. Finally, for any condition to cause dyspnea, there must be sensory perceptions related to breathing and ventilatory stimuli.
Acute dyspnea: Dyspnea developing over minutes to days most often reflects an acute cardiac or pulmonary process. Cardiovascular causes include thromboembolism, pericardial disease, and pulmonary edema due to myocardial or valvular dysfunction. Pulmonary processes likely in this context include diffuse airway obstruction; pneumonia; upper airway obstruction; compression of the lung by chest wall trauma or diaphragmatic or pleural processes; rapidly progressive inflammatory disease; or diffuse lung injury with noncardiogenic pulmonary edema.
Chronic dyspnea: Longstanding dyspnea is more likely to present diagnostic difficulty. Table 351.1 categorizes causes of chronic dyspnea according to pathophysiologic mechanism.
HISTORY AND PHYSICAL EXAMINATION
It is important to establish the acuity of the symptoms and to determine the patient’s current and past activity levels. Patients may have unconsciously reduced their activity levels to avoid symptoms of breathlessness. One should identify environmental, temporal, and postural factors that worsen the symptoms and ask about associated symptoms such as chest pain, cough, or syncope. The physical examination has to be comprehensive. Although attention should be directed at cardiorespiratory findings, signs of systemic diseases such as collagen vascular disorders, thyroid disease, or neurologic syndromes also should be sought.
LABORATORY STUDIES AND DIAGNOSTIC TESTS
Acute dyspnea: For acutely ill patients, chest radiography to evaluate for pulmonary infiltrates or edema and arterial blood gas analysis to assess the adequacy of gas exchange are almost always indicated. Peak expiratory flow rates provide an objective measure of the severity of airflow obstruction among patients with airway disease. Electrocardiography (ECG) is indicated whenever cardiac disease is known or suspected. Additional studies that might be indicated on the basis of the initial evaluation include perfusion lung scanning to evaluate for thromboembolism, echocardiography to assess valvular or ventricular dysfunction, and analysis of respiratory secretions or lung tissue to identify infectious agents or noninfectious inflammatory processes.
Chronic dyspnea: The cause often is evident from the results of history, examination, and basic screening tests such as hematocrit and blood chemistries. Additional tests should be selected with specific goals; no set sequence of diagnostic studies can be recommended. The most useful tests usually are measures of pulmonary function, including simple spirometry, lung volume, and diffusing capacity. Chest radiography usually is indicated to demonstrate focal or diffuse disease of the lung parenchyma and to assess cardiac size. Exercise testing may uncover dysfunction of a diseased organ system that had been adequately compensated at rest. A comprehensive exercise test includes measurement of respiratory gas exchange, ventilation, heart rate and blood pressure, ECG, pulse oximetry, and when appropriate, arterial blood gas analysis. The following studies are reserved for selected patients: spirometry with bronchoprovocation when asthma is suspected despite normal results of pulmonary function tests, echocardiography chiefly for identifying valvular lesions and resting or exercise ventricular dysfunction, bronchoscopy for finding focal obstructing lesions of the airways, and computed tomography for confirming the presence of interstitial inflammatory diseases, which may require histologic examination for specific diagnosis.