GENERAL APPROACH TO RESPIRATORY DISTRESS
INTRODUCTION AND DEFINITIONS
Dyspnea is a feeling of difficult, labored, or uncomfortable breathing, often described as “shortness of breath,” “breathlessness,” or “not getting enough air.”1-3 Dyspnea is usually caused by pulmonary or cardiac disease. Tachypnea is rapid breathing. Orthopnea is dyspnea in the recumbent position; it is most often the result of left ventricular failure but can 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 lying on one side (lateral decubitus position) but not the other side. Trepopnea can occur when one lung is more diseased than the other and the patient lies on the side of the more affected lung where gravity increases blood flow to the worse lung and reduces it to the better lung.4 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 from multiple pathophysiologic mechanisms.1 Sensory information about respiratory activity generated by multiple afferent receptors integrates within the CNS at both the subcortical and cortical levels. The sensation of dyspnea occurs 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).5-8 Physical signs associated with dyspnea include tachypnea and tachycardia; use of the accessory respiratory muscles, including the sternocleidomastoid, sternoclavicular, and intercostals; nasal flaring; 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.2,9
TABLE 62-1Common Causes of Dyspnea in the ED |Favorite Table|Download (.pdf) TABLE 62-1 Common Causes of Dyspnea in the ED
Most Common Causes
Obstructive airway disease: asthma, chronic obstructive pulmonary disease
Decompensated heart failure/cardiogenic pulmonary edema
Ischemic heart disease: unstable angina and myocardial infarction
Most Immediately Life-Threatening Causes
Upper airway obstruction: foreign body, angioedema, hemorrhage
Neuromuscular weakness: myasthenia gravis, Guillain-Barré syndrome, botulism