INTRODUCTION

Dyspnea is the perception of an inability to breathe comfortably [1]. The adult patient with acute dyspnea presents difficult challenges in diagnosis and management. The emergency clinician must work through a wide differential diagnosis while providing appropriate initial treatment for a potentially life-threatening illness. Airway, breathing, and circulation are the emergency clinician's primary focus when beginning management of the acutely dyspneic patient. Once these are stabilized, further clinical investigation and treatment can proceed.

For the purpose of this review, we will use the term "dyspnea" to encompass all patients with disordered or inadequate breathing. This topic review will provide a differential diagnosis of the life-threatening and common causes of dyspnea in the adult, describe important historical and clinical findings that can help to narrow the differential diagnosis, discuss the use of common diagnostic studies, and provide recommendations for initial management and disposition. Detailed discussions of specific diagnoses are found elsewhere in the program.

PATHOPHYSIOLOGY

The respiratory system is designed to maintain homeostasis with respect to gas exchange and acid-base status. Derangements in oxygenation as well as acidemia lead to breathing discomfort. The development of dyspnea is a complex phenomenon generally involving stimulation of a variety of mechanoreceptors throughout the upper airway, lungs, and chest wall, and chemoreceptors at the carotid sinus and the medulla. The pathophysiology of dyspnea is discussed in detail elsewhere. (See "Physiology of dyspnea" and "Oxygenation and mechanisms of hypoxemia".)

EPIDEMIOLOGY

Dyspnea is a common chief complaint among patients who come to the emergency department (ED). A chief complaint of dyspnea or shortness of breath made up 3.5 percent of the more than 115 million visits to United States EDs in 2003. Other dyspnea-related chief complaints (cough, chest discomfort) comprised 7.6 percent [2].

According to one prospective observational study, the most common diagnoses among elderly patients presenting to an ED with a complaint of acute shortness of breath and manifesting signs of respiratory distress (eg, respiratory rate >25, SpO2 <93 percent) are decompensated heart failure, pneumonia, chronic obstructive pulmonary disease, pulmonary embolism, and asthma [3].