부산대학교 도서관

Summary Inadequate gas exchange (respiratory failure) is the most common reason for admission to critical care and associated with high mortality rates. Effective gas exchange requires adequate ventilation, diffusion, and perfusion. Hypoxaemia (low blood oxygen saturation) will result if any of these are inadequate, whereas hypercapnia typically results from inadequate ventilation. Two different types of respiratory failure can be considered clinically—normocapnic (sometimes called ‘Type 1’), where oxygenation is impaired but ventilation and therefore clearance of carbon dioxide (CO2) is not, and hypercapnic (‘Type 2’), where inadequate ventilation impairs CO2 clearance as well as oxygenation. In physiological terms—and regardless of the underlying disease process—hypoxaemia always results from one of five possible causes: less inspired oxygen (e.g. high altitude), hypoventilation, impaired diffusion across the alveolar membrane, inequality of ventilation and perfusion (‘V/Q mismatch’), and shunting (blood flow that does not participate in gas exchange). Increasing the inspired oxygen may seem the obvious treatment for respiratory failure; however, unnecessary hyperoxia likely also carries inherent risk of harm and may not fully resolve the situation either. This chapter reviews these topics in detail and considers how investigations (e.g. arterial blood gases) can be used to target respiratory failure treatment.