Pathophysiology
Clinical meaning
Acute respiratory failure occurs when the respiratory system fails to maintain adequate gas exchange, classified as Type I (hypoxemic, PaO2 < 60 mmHg) or Type II (hypercapnic, PaCO2 > 50 mmHg with acidosis). Type I failure results from ventilation-perfusion (V/Q) mismatch, shunt, or diffusion impairment seen in pneumonia, pulmonary edema, ARDS, and pulmonary embolism. Type II failure results from inadequate alveolar ventilation due to respiratory center depression (opioids, brainstem injury), neuromuscular disease (Guillain-Barré, myasthenia gravis), or severe airway obstruction (COPD exacerbation, asthma). Early signs include restlessness, anxiety, tachypnea, and accessory muscle use. Late signs include confusion, lethargy, cyanosis, and bradycardia indicating imminent respiratory arrest. Oxygen supplementation treats Type I failure, while ventilatory support (BiPAP or intubation) is needed for Type II failure.