GENERAL APPROACH TO RESPIRATORY DISTRESS
Dyspnea is a subjective feeling of difficult, labored, or uncomfortable breathing, which patients often describe as "shortness of breath," "breathlessness," or "not getting enough air."1 Dyspnea is frequently associated with other respiratory symptoms or signs. Tachypnea is rapid breathing. Orthopnea is dyspnea in the recumbent position. It is most often the result of left ventricular failure, but can also be seen with diaphragmatic paralysis or chronic obstructive pulmonary disease. Paroxysmal nocturnal dyspnea is orthopnea that awakens the patient from sleep, prompting an upright posture in order to resolve breathlessness. Trepopnea is dyspnea associated with only one of several recumbent positions. Trepopnea can occur with unilateral diaphragmatic paralysis, with ball-valve airway obstruction, or after surgical pneumonectomy. Platypnea is the opposite of orthopnea: dyspnea in the upright position. Platypnea results from the loss of abdominal wall muscular tone and, in rare cases, from right-to-left intracardiac shunting, as occurs from a patent foramen ovale. Hyperpnea is essentially hyperventilation and is defined as minute ventilation in excess of metabolic demand. Respiratory distress is a term used by the physician, combining the patient's subjective sensation of dyspnea with signs indicating difficulty breathing. Ventilatory or respiratory failure occurs when the lungs and ventilatory muscles cannot move enough air in and out of the alveoli to adequately oxygenate arterial blood and eliminate carbon dioxide.
Dyspnea is a complex sensation that arises from the interaction of multiple pathophysiologic mechanisms.1,2 Sensory information about respiratory activity generated by multiple afferent receptors is integrated within the CNS at both the subcortical and cortical levels. The current explanation for the sensation of dyspnea is when imbalance exists among the inspiratory drive, efferent activity to the respiratory muscles, and feedback from these afferent receptors.
Dyspnea is a feature of several disorders seen in the ED (Table 62-1). The presence or degree of dyspnea is difficult to measure, although categorical scales (e.g., the Borg or Fletcher scales) and visual analog scales can be used to gauge response to therapy.1,3 Assess for evidence of impending respiratory failure: marked tachypnea and tachycardia; stridor; use of the accessory respiratory muscles, including the sternocleidomastoid, sternoclavicular, and intercostals; inability to speak normally as a consequence of breathlessness; agitation or lethargy as a consequence of hypoxemia; depressed consciousness due to hypercapnia; and paradoxical abdominal wall movement when the abdominal wall retracts inward with inspiration, indicating diaphragmatic fatigue. In patients with these signs, give oxygen and be prepared for more advanced measures (discussed elsewhere). Lesser degrees of dyspnea allow for a more detailed medical history, physical examination, and indicated ancillary tests.
TABLE 62-1Common Causes of Dyspnea in the ED