Hypoxemia

Hypoxemia is a lower-than-normal level of oxygen in arterial blood, usually defined by a reduced partial pressure of arterial oxygen (PaO2) or decreased arterial oxygen saturation (SaO2). At sea level, normal PaO2 is about 75–100 mmHg and SaO2 is about 95–100%. Hypoxemia can occur with or without symptoms and is not the same as hypoxia, which denotes inadequate oxygen delivery to tissues.

Causes and mechanisms include ventilation-perfusion mismatch, diffusion impairment, and intracardiac or intrapulmonary shunts, as well as reduced inspired oxygen tension from high altitude or hypoventilation. Common conditions associated with hypoxemia are chronic obstructive pulmonary disease, interstitial lung disease, pneumonia, acute respiratory distress syndrome, pulmonary edema, pulmonary embolism, and obesity hypoventilation syndrome. Acute events such as surgery or trauma can also produce hypoxemia.

Assessment typically involves arterial blood gas analysis to measure PaO2 and SaO2, and pulse oximetry for continuous noninvasive monitoring. The PaO2/FiO2 ratio is used to assess the severity of hypoxemia in respiratory failure. Clinically, signs may include tachypnea, tachycardia, cyanosis, or altered mental status, though presentation varies.

Management focuses on resolving the underlying cause and restoring adequate oxygenation. Supplemental oxygen is standard, with targets often keeping SpO2 in the range of 92–96% (or 88–92% in some COPD cases). Severe cases may require noninvasive or invasive mechanical ventilation, and treatment is guided by the specific etiology, with careful monitoring for CO2 retention in susceptible patients.