Hypoxic

Hypoxic is an adjective describing conditions related to hypoxia, a deficiency in the amount of oxygen that reaches tissues. Hypoxia can affect any organ, but the brain and heart are particularly sensitive. The term is used in clinical and physiological contexts to describe regions or periods of inadequate oxygenation.

There are several mechanisms by which hypoxia occurs. Hypoxic (or hypoxemic) hypoxia results from low arterial oxygen tension, which can arise from high altitude, lung disease, or impaired gas exchange. Anemic hypoxia occurs when there is insufficient functional hemoglobin to carry oxygen, even if the lungs and blood flow are normal. Circulatory or stagnant hypoxia is due to reduced blood flow, limiting oxygen delivery to tissues. Histotoxic hypoxia happens when cells cannot utilize oxygen effectively, as seen with certain toxins such as cyanide. In practice, mixtures of these mechanisms can contribute to tissue hypoxia.

Diagnosis relies on measurements of oxygen in the blood and tissues. Arterial blood gas testing can show low PaO2, while pulse oximetry indicates reduced oxygen saturation (SaO2). Lactate levels may rise with anaerobic metabolism during hypoxia. Chronic hypoxia can trigger compensatory changes, such as increased red blood cell production (polycythemia).

Management aims to restore oxygen delivery and correct the underlying cause. This may involve supplemental oxygen or mechanical ventilation, treatment of lung disease, measures to improve blood flow, transfusion for anemia, or antidotes and supportive care for toxic causes. Distinguishing hypoxic from ischemic or histotoxic etiologies guides appropriate therapy and prognosis.