28 Shortness of Breath
Dyspnea, or breathlessness, has been defined as patient awareness of respiratory discomfort, unpleasant sensation of labored breathing, or shortness of breath. Dyspnea can be caused by increased rigidity of lung tissue, increased airway resistance, enhanced ventilation during exercise, or any combination of these factors.
Some investigators have suggested that determining the cause of dyspnea is often facilitated by first classifying it into different types, such as wheezing dyspnea, dyspnea on exertion, paroxysmal nocturnal dyspnea, hyperventilation, and dyspnea of cerebral origin. Perhaps a simpler classification is acute, chronic, or recurrent. The common causes of dyspnea include chronic obstructive pulmonary disease (COPD), asthma, congestive heart failure (CHF), anxiety, obesity, and poor physical condition.
Acute dyspnea in children is most frequently caused by asthma, bronchiolitis, croup, and epiglottitis. On rare occasions, it may result from foreign body aspiration. An acute onset of dyspnea in a woman who is pregnant or is taking oral contraceptives suggests pulmonary embolism. Pulmonary embolism should also be suspected if dyspnea occurs in patients who have recently undergone surgery, in people who have had prolonged recumbency, and in patients who have a history of phlebitis or cardiac arrhythmias (dysrhythmias).
The most common cause of chronic and recurrent shortness of breath in children is asthma. In children, a nocturnal cough or nocturnal wheezing is due to asthma until proven otherwise. In elderly patients, chronic dyspnea is frequently caused by COPD and heart failure, which are rare conditions in patients younger than 30 years. As dyspnea develops in these elderly patients, they decrease their physical activity; the resulting deconditioning confounds the clinical picture.
In the elderly, the most common causes of dyspnea are heart failure, chronic obstructive lung disease, and asthma. Other common causes are pneumonia and parenchymal lung disease. Acute dyspnea in the elderly can be caused by heart failure, asthma, COPD, pulmonary embolism, pneumonia, and pneumothorax.
Chronic dyspnea is more common in people who are heavy smokers, because smoking is one of the most important factors in the development of emphysema, chronic bronchitis, and COPD. Obese and physically inactive patients frequently complain of recurrent dyspnea on minimal exertion because of their poor cardiopulmonary reserve.
The duration of dyspnea, precipitating factors such as exercise and exposure to allergens, nighttime and/or daytime occurrence, the number of pillows used when sleeping, concomitant coughing, chest pain, and palpitations are factors that assist the physician in making an accurate diagnosis.
In patients with acute dyspnea, the physician should consider the possibility of pulmonary embolus, asthma, upper airway obstruction, foreign body aspiration, panic disorder, hyperventilation, pneumonia, pneumothorax, pulmonary edema, and, occasionally, respiratory failure. Asthma is usually episodic and often precipitated by allergens, exercise, cold exposure, or infections. It is characterized by bilateral wheezing and a decreased respiratory flow rate.
Upper airway obstruction can be caused by aspiration, vocal cord paralysis, tumors, and epiglottic and laryngeal edema. In cases of foreign body aspiration (more common in children) the onset of respiratory difficulty is acute. When acute respiratory difficulty occurs during eating, especially in the intoxicated or semiconscious patient, foreign body aspiration is probable. When complete respiratory obstruction occurs, severe respiratory distress, cyanosis, gasping, and loss of consciousness occur quickly. Incomplete respiratory obstruction causes tachypnea, inspiratory stridor, and localized wheezing.
Patients with acute dyspnea due to hyperventilation are usually anxious. They often complain of numbness and tingling in the perioral region and the extremities. These patients also often complain of lightheadedness, sighing respiration, and an inability to “get enough air in.”
When dyspnea occurs in one lateral position but not in the other (trepopnea), unilateral lung disease, pleural effusion, or obstruction of the proximal tracheobronchial tree should be suspected. Dyspnea in the upright position that is relieved by recumbency (platypnea) may be seen in patients with intracardiac shunts, vascular lung shunts, and parenchymal lung shunts.
When chest pain accompanies acute dyspnea, spontaneous pneumothorax, pulmonary embolism, chest trauma, and myocardial infarction should be suspected. Pulmonary embolism is a common cause of acute dyspnea in adults. Patients usually appear severely ill and may also complain of chest pain, faintness, and, occasionally, loss of consciousness. Peripheral cyanosis, low blood pressure, and rales may be present.
When fever, chills, and cough are associated with acute dyspnea, pneumonia is most likely. When dyspnea on exertion, paroxysmal nocturnal dyspnea, and peripheral edema are associated with chronic or acute dyspnea, heart failure is most likely. Pulmonary embolism is most often associated with pleuritic pain, cough, leg swelling, or leg pain and occasionally with wheezing and hemoptysis.
When acute dyspnea is caused by severe anemia of acute onset, associated symptoms include dizziness, weakness, and sweating and, possibly, signs of hemorrhage (e.g., hypotension, tachycardia, rapid and shallow respirations). When acute dyspnea is a manifestation of anxiety or panic disorder, the patient also usually complains of dizziness, lightheadedness, palpitations, and paresthesias. The patients do not appear dyspneic and often complain of “not being able to take in enough air.” Patients who complain of dyspnea at rest have either a severe physiologic impairment or anxiety hyperventilation.
The most common causes of chronic dyspnea on exertion are cardiac and pulmonary. Although paroxysmal nocturnal dyspnea is most frequently caused by cardiac pathology, some asthmatic patients experience symptoms primarily when recumbent, usually at night. Associated findings are often helpful in differentiating pulmonary from cardiac causes of dyspnea. When dyspnea is caused primarily by lung disease, the dyspnea is intensified by effort, there is a daily productive cough, the respirations are shallow and rapid, and postural changes have little or no effect. When dyspnea has a cardiac cause, it is intensified by recumbency and the respirations are shallow but not necessarily rapid.
Other clues also help differentiate pulmonary from cardiac causes of dyspnea on exertion. When the cause is pulmonary, the rate of recovery to normal respiration is fast, and dyspnea abates a few minutes after cessation of exercise. However, patients with dyspnea due to cardiac causes remain dyspneic much longer after cessation of exercise. Likewise, in these patients, the heart rate also takes longer to return to pre-exercise levels. Patients with pulmonary dyspnea do not usually have dyspnea at rest. Patients with severe cardiac dyspnea demonstrate a volume of respiration that is greater than normal at all levels of exercise; they also experience dyspnea sooner after the start of exertion.