Causes of respiratory distress are multifactorial and include the findings of dyspnea, hypoxia, hypercapnia, and cyanosis. Despite the increasing reliance on ancillary studies and technology, the evaluation of respiratory distress depends on a careful history and physical examination.
Dyspnea is the subjective feeling of difficult, labored, or uncomfortable breathing. There is no single pathophysiologic mechanism that causes dyspnea. However, most patients with dyspnea have a cardiac or a pulmonary cause.
The initial assessment of any patient with dyspnea should be directed toward identifying respiratory failure. Dyspnea is a subjective complaint difficult to quantify. Vital signs (including pulse oximetry) and general impression will identify those in significant distress. Tachycardia, tachypnea, stridor, and the use of accessory respiratory muscles point to significant respiratory distress. Other significant signs include lethargy, agitation, altered mental status, and inability to speak due to breathlessness. In patients with any of these signs or symptoms, oxygen should be administered immediately. When there is no improvement, the need for aggressive airway management and mechanical ventilation should be anticipated. Lack of these significant signs and symptoms indicates a lesser degree of distress, thereby allowing for a detailed history and physical examination that often may help identify the etiology of dyspnea.
Diagnosis and Differential
The history and physical examination should be the primary aids in identifying the etiology of dyspnea. However, ancillary testing may aid in determining the severity and specific cause (Table 29-1). Overall clinical gestalt is important, as are specific findings of an S3 gallop and jugular venous distention. Pulse oximetry is a rapid but insensitive screen for disorders of gas exchange. Arterial blood gas (ABG) analysis has improved sensitivity but does not take into account work of breathing. ABG analysis may also demonstrate a metabolic acidosis, which can be a common cause of hyperpnea. A chest radiograph may identify pulmonary and cardiac causes of dyspnea. In addition, an abnormal electrocardiogram or elevated cardiac enzymes may point toward a cardiac cause of dyspnea. A peak expiratory flow rate may indicate reactive airway disease. Additional laboratory tests that may prove helpful include a complete blood count, B-type natriuretic peptide, and D-dimer assay. Uncommonly, the cause of dyspnea may not be identified. Specialized testing that may be indicated include computed tomography of the chest, echocardiography, pulmonary function testing, cardiac stress testing, nuclear medicine scans, or combined cardiopulmonary exercise testing.
Table 29-1 Causes of Dyspnea ||Download (.pdf)
Table 29-1 Causes of Dyspnea
|Most Common Causes||Most Immediately Life-Threatening|
|Obstructive airway disease; asthma, COPD||Upper airway obstruction: foreign body, angioedema, hemorrhage|
|Congestive heart failure/cardiogenic pulmonary edema||Tension pneumothorax|
|Ischemic heart disease: unstable angina and myocardial infarction||Pulmonary embolism|
|Pneumonia||Neuromuscular weakness: myasthenia gravis, Guillain-Barré syndrome, botulism|
Emergency Department Care and Disposition