Hypoxia: physiological causes

Hypoxia management in the intensive care unit requires addressing underlying physiological causes rather than reflexively increasing the fraction of inspired oxygen (FiO2). While increasing oxygen concentration provides a temporary fix, it fails to treat the root pathology in four out of five primary causes of hypoxia: shunt, dead space, diffusion abnormalities, and hypoventilation. Effective clinical assessment involves distinguishing between oxygenation, which relies on diffusion, and ventilation, which requires convective gas movement. For instance, nitrogen washout illustrates how excessive oxygen can exacerbate atelectasis by removing the stabilizing nitrogen in the alveoli. Clinicians must systematically investigate factors like pulmonary embolism, pneumonia, or mechanical ventilator failure to provide definitive treatment. Relying solely on oxygen supplementation ignores the mechanical or pathological barriers to gas exchange, often delaying necessary interventions such as anticoagulation, antibiotics, or lung-protective ventilation strategies.