Hypoxia

Hypoxia is a condition in which tissues are deprived of an adequate oxygen supply, leading to cellular stress and potential dysfunction. It reflects inadequate oxygen delivery to cells, which can occur even when blood oxygen levels are normal if delivery or utilization is impaired. Hypoxia is distinct from hypoxemia, which specifically denotes reduced oxygen content in the arterial blood; hypoxia refers to tissue-level oxygen deficiency.

There are several forms of hypoxia. Hypoxic (or hypoxemic) hypoxia results from insufficient oxygen in the lungs or impaired transfer of oxygen to the blood, such as at high altitude, due to ventilation-perfusion mismatch, or diffusion impairment. Anemic hypoxia occurs when oxygen transport is reduced because of low hemoglobin or dysfunctional hemoglobin. Circulatory (ischemic) hypoxia arises from inadequate blood flow to tissues, as seen in shock or heart failure. Histotoxic hypoxia happens when cells cannot utilize oxygen effectively, as in cyanide poisoning or certain metabolic toxins.

Causes are varied and include respiratory diseases (chronic obstructive pulmonary disease, pneumonia), acute lung injury, severe asthma, airway obstruction, anemia, carbon monoxide exposure, methemoglobinemia, cardiovascular collapse, and toxin exposure. The underlying pathophysiology involves a failure to meet tissue oxygen demand, leading to shifts toward anaerobic metabolism and lactate accumulation, with potential organ dysfunction if prolonged.

Common signs and diagnostic approaches include shortness of breath, rapid or shallow breathing, tachycardia, confusion, or agitation. Measurement tools include pulse oximetry and arterial blood gas analysis, which assess oxygen saturation, partial pressure of oxygen, and other parameters. Evaluation also seeks the underlying cause through history, imaging, and laboratory tests.

Treatment targets the cause and the oxygen supply. Supplemental oxygen is a cornerstone, with escalation to advanced support such as ventilation when needed. Specific interventions include treating anemia, removing or counteracting toxins (for example, hyperbaric oxygen for certain poisonings, methylene blue for methemoglobinemia), and addressing altitude exposure or cardiovascular compromise. Prognosis hinges on the cause, duration, and the speed of restoration of adequate tissue oxygenation.