DYSPNEA

ESSENTIAL INQUIRIES

Fever.
Cough.
Chest pain.
Vital sign measurements; pulse oximetry.
Cardiac and chest examination.
Chest radiography.
Arterial blood gas measurement.

General Considerations

Dyspnea is a subjective experience or perception of uncomfortable breathing. However, the relationship between level of dyspnea and the severity of underlying disease varies widely across individuals. Dyspnea can result from conditions that increase the mechanical effort of breathing (eg, COPD, restrictive lung disease, respiratory muscle weakness), from conditions that produce compensatory tachypnea (eg, hypoxemia or acidosis), or from psychogenic origins. The following factors play a role in how and when dyspnea presents in patients: rate of onset, previous dyspnea, medications, comorbidities, psychological profile, and the severity of underlying disorder. In patients with established COPD, the patient-reported severity of dyspnea is superior to forced expiratory volume in 1 second (FEV1) in predicting quality of life and 5-year mortality.

Clinical Findings

A. Symptoms

The duration, severity, and periodicity of dyspnea influence the tempo of the clinical evaluation. Rapid onset, severe dyspnea in the absence of other clinical features should raise concern for pneumothorax, pulmonary embolism, or increased left ventricular end-diastolic pressure (LVEDP). Spontaneous pneumothorax is usually accompanied by chest pain and occurs most often in thin, young males, or in those with underlying lung disease. Pulmonary embolism should always be suspected when a patient with new dyspnea reports a recent history (previous 4 weeks) of prolonged immobilization, estrogen therapy, or other risk factors for deep venous thrombosis (DVT) (eg, previous history of thromboembolism, cancer, obesity, lower extremity trauma) and when the cause of dyspnea is not apparent. Silent myocardial infarction, which occurs more frequently in diabetic persons and women, can result in acute heart failure and dyspnea.

Accompanying symptoms provide important clues to various etiologies of dyspnea. When cough and fever are present, pulmonary disease (particularly infections) is the primary concern, although myocarditis, pericarditis, and septic emboli can also present in this manner. Chest pain should be further characterized as acute or chronic, pleuritic or exertional. Although acute pleuritic chest pain is
the rule in acute pericarditis and pneumothorax, must patients with pleuritic chest pain in the outpatient clinic have pleurisy due to acute viral respiratory tract infection. Periodic chest pain that precedes the onset of dyspnea is suspicious for myocardial ischemia as well as pulmonary embolism. When associated with wheezing, most cases of dyspnea are due to acute bronchitis; however, when acute bronchitis seems unlikely, the clinician should also consider new-onset asthma, foreign body, and vocal cord dysfunction.

When a patient reports prominent dyspnea with mild or no accompanying features, consider noncardiopulmonary causes of impaired oxygen delivery (anemia, methemoglobinemia, cyanide ingestion, carbon monoxide), metabolic acidosis due to a variety of conditions, panic disorder, and chronic pulmonary embolism.

B. Physical Examination

A focused physical examination should include evaluation of the head and neck, chest, heart, and lower extremities. Visual inspection of the patient’s respiratory pattern can suggest obstructive airway disease (pursed-lip breathing, use of extra respiratory muscles, barrel-shaped chest), pneumothorax (asymmetric excursion), or metabolic acidosis (Kussmaul respirations). Patients with impending upper airway obstruction (eg, epiglottitis, foreign body), or severe asthma exacerbation, sometimes assume a tripod position. Focal wheezing raises the suspicion for a foreign body or other bronchial obstruction. Maximum laryngeal height (the distance between the top of the thyroid cartilage and the suprasternal notch at end expiration) is a measure of hyperinflation. Obstructive airway disease is virtually nonexistent when a nonsmoking patient younger than 45 years has a maximum laryngeal height ≤ 4 cm (Table 2–2). Absent breath sounds suggests a pneumothorax. An accentuated pulmonic component of the second heart sound (loud P2) is a sign of pulmonary hypertension and pulmonary embolism.

A systematic review has identified several clinical predictors of increased LVEDP useful in the evaluation of dyspneic patients with no prior history of CHF (Table 2–3). When none is present, there is a very low probability (< 10%) of increased LVEDP, and when two or more are present, there is a very high probability (> 90%) of increased LVEDP.

C. Diagnostic Studies

Causes of dyspnea that can be managed without chest radiography are few: ingestions causing lactic acidosis, methemoglobinemia, and carbon monoxide poisoning. The diagnosis of pneumonia should be confirmed by chest radiography in most patients. When COPD exacerbation is severe enough to require hospitalization, results of chest radiography can influence management decisions in up to 20% of patients. Chest radiography is fairly sensitive and specific for new-onset CHF (represented by redistribution of pulmonary venous circulation) and can help guide treatment decisions in patients with dyspnea secondary to cardiac disease. End-expiratory chest radiography enhances detection of a small pneumothorax.

A normal chest radiograph has substantial diagnostic value. When there is no physical examination evidence of COPD or CHF and the chest radiograph is normal, the major remaining causes of dyspnea include pulmonary embolism, Pneumocystis jiroveci infection (initial radiograph may be normal in up to 25% ), upper airway obstruction, foreign body, anemia, and metabolic acidosis. If a patient has tachycardia and hypoxemia but a normal chest radiograph and electrocardiogram (ECG), then further tests to exclude pulmonary emboli are warranted (see Chapter 9), provided blood tests exclude significant anemia or metabolic acidosis. High-resolution chest CT is particularly useful in the evaluation of pulmonary embolism and has the added benefit of providing information about interstitial and alveolar lung disease.

Serum or whole blood brain natriuretic peptide (BNP or NT-proBNP) testing can be useful in distinguishing cardiac from noncardiac causes of dyspnea in the emergency department, since elevated BNP levels are both sensitive and specific for increased LVEDP in symptomatic persons. Cut points for ruling out acute heart failure increase with age, with one study recommending < 300  g/L to rule out heart failure, and three cut points for ruling-in heart failure (> 450 ng/L for age < 50 years; > 900 ng/L for age 50–75 years; and > 1800 ng/L for age > 75 years).

Persistent uncertainty following clinical examination and routine diagnostic testing warrants arterial blood gas measurement. With two notable exceptions (carbon monoxide poisoning and cyanide toxicity), arterial blood gas measurement distinguishes increased mechanical effort causes of dyspnea (respiratory acidosis with or without hypoxemia) from compensatory tachypnea (respiratory alkalosis with or without hypoxemia or metabolic acidosis) from psychogenic dyspnea (respiratory alkalosis). Carbon monoxide and cyanide impair oxygen delivery with minimal alterations in Po2; percent carboxyhemoglobin identifies carbon monoxide toxicity. Cyanide poisoning should be considered in a patient with profound lactic acidosis following exposure to burning vinyl (such as a theater fire or industrial accident). Suspected carbon monoxide poisoning or methemoglobinemia can also be confirmed with venous carboxyhemoglobin or methemoglobin levels.

Because arterial blood gas testing is impractical in most outpatient settings, pulse oximetry has assumed a central role in the office evaluation of dyspnea. Oxygen saturation values above 96% almost always correspond with a Po2 > 70 mm Hg, and values < 94% almost always represent clinically significant hypoxemia. Important exceptions to this rule include carbon monoxide toxicity, which leads to a normal oxygen saturation (due to the similar wavelengths of oxyhemoglobin and carboxyhemoglobin), and methemoglobinemia, which results in an oxygen saturation of about 85% that fails to increase with supplemental oxygen. A delirious or obtunded patient with obstructive lung disease warrants immediate measurement of arterial blood gases to exclude hypercapnia and the need for intubation, regardless of the oxygen saturation. When pulse oximetry yields equivocal results, assessment of desaturation with ambulation (eg, a brisk walk around the clinic) can be a useful finding (eg, when Pneumocystis jiroveci pneumonia is suspected) for confirming impaired gas exchange.

Episodic dyspnea can be challenging if an evaluation cannot be performed during symptoms. Life-threatening causes include recurrent pulmonary embolism, myocardial ischemia, and reactive airway disease. When associated with audible wheezing, vocal cord dysfunction should be considered, particularly in a young woman who does not respond to asthma therapy. Spirometry is very helpful in further classifying patients with obstructive airway disease but is rarely needed in the initial or emergent evaluation of patients with acute dyspnea.

Differential Diagnosis

Acute dyspnea, particularly as the chief complaint, demands urgent evaluation. Urgent and emergent conditions causing acute dyspnea include pneumonia, COPD, asthma, pneumothorax, pulmonary embolism, cardiac disease (eg, CHF, acute myocardial infarction, valvular dysfunction, arrhythmia, cardiac shunt), metabolic acidosis, cyanide toxicity, methemoglobinemia, and carbon monoxide poisoning. 

Treatment

The treatment of urgent or emergent causes of dyspnea should aim to relieve the underlying cause. Pending diagnosis, patients with hypoxemia should be immediately provided supplemental oxygen unless significant hypercapnia is present or strongly suspected pending arterial blood gas measurement. Dyspnea frequently occurs in patients nearing the end of life; whereas opioid therapy can provide substantial relief independent of the severity of hypoxemia, oxygen therapy appears to be most beneficial to patients with significant hypoxemia (see Chapter 5). There appears to be limited benefit of supplemental oxygen when patients with life-limiting illness have Pao2 > 55 mm Hg. In patients with severe COPD and hypoxemia, oxygen therapy improves mortality and exercise performance. Current clinical trials are attempting to determine benefits of supplemental oxygen in patients with COPD and moderate hypoxemia at rest or desaturation with exercise. Pulmonary rehabilitation programs are another therapeutic option for patients with moderate to severe COPD or interstitial pulmonary fibrosis.

When to Refer

• Patients with advanced COPD should be referred to a pulmonologist, and patients with CHF or valvular heart disease should be referred to a cardiologist following acute stabilization.
• Cyanide toxicity should be managed in conjunction with a toxicologis.

When to Admit

• Impaired gas exchange from any cause or high risk of pulmonary embolism pending definitive diagnosis.
• Suspected cyanide poisoning.