Hypoksemia

Hypoksemia is a condition of abnormally low oxygen in arterial blood. Clinically it is defined by a reduced PaO2 or SaO2, commonly PaO2 <80 mmHg or SaO2 <95% at sea level, though thresholds vary with altitude and testing method. It lowers arterial oxygen content (CaO2) and may reflect reduced oxygen uptake, transport, or delivery.

Causes include decreased inspired oxygen (high altitude, airway obstruction), hypoventilation, diffusion impairment, ventilation–perfusion mismatch, and shunt. Anemia or abnormal hemoglobin can reduce oxygen content even with normal PaO2.

Symptoms range from dyspnea and tachypnea to confusion and tachycardia. Cyanosis is not always present, especially in chronic hypoxemia or anemia.

Diagnosis relies on arterial blood gas measurement of PaO2, PaCO2, and SaO2, supported by pulse oximetry. Further evaluation includes chest imaging and tests to identify causes, such as ventilation–perfusion scans or diffusion studies.

Management targets the underlying cause and improving oxygen delivery; supplementary oxygen is common, and mechanical ventilation may be required for severe cases. Chronic hypoxemia is managed with long-term oxygen therapy and treatment of the underlying disease. Prognosis depends on the cause and response to therapy.