Acute respiratory failure. Pathophysiology, causes, and clinical manifestations.

Acute respiratory failure is a common life-threatening process with myriad causes. It is characterized by a failure of oxygenation or ventilation, or both. Hypoxemia is common to all causes of respiratory failure, whereas PaCO2 may be normal, decreased, or elevated. These abnormalities result from several pathophysiologic processes, including intrapulmonary venoarterial shunt, alveolar hypoventilation, diffusion impairment, and ventilation-perfusion mismatch. Type I failure results from processes that lead to hypocapnia or normocapnia; type II failure is distinguished by the presence of hypercapnia. The clinical manifestations of acute respiratory failure are nonspecific; for this reason, a high index of suspicion and early examination of arterial blood gases are essential to successful management.