低酸素症

Hypoxia is categorized into four types based on cause. Anemic hypoxia results from insufficient red blood cells or abnormal hemoglobin. Ischemic hypoxia occurs when blood circulation to tissues is impaired or blocked. Histotoxic hypoxia happens when cells cannot utilize delivered oxygen due to toxins like cyanide. Hypoxemic hypoxia involves low arterial oxygen pressure from pulmonary diseases or low environmental oxygen.

Carbon monoxide binds to hemoglobin with over 200 times greater affinity than oxygen, displacing oxygen from its binding sites. This reduces hemoglobin's oxygen-carrying capacity and lowers arterial oxygen pressure, creating a severe form of hypoxemic hypoxia. Even trace amounts of carbon monoxide can cause life-threatening hypoxia.

Hypoxia is detected through bluish discoloration of the skin and mucosae, particularly visible in nailbeds. This cyanosis becomes apparent when hemoglobin saturation drops below 75%, and is especially noticeable in fair-skinned individuals. The discoloration reflects inadequate oxygen supply to body tissues.

Treatment involves administering 100% oxygen at normal atmospheric pressure or using hyperbaric oxygen chambers that supply higher-than-normal oxygen levels. These methods effectively displace carbon monoxide from hemoglobin, providing life-saving intervention. Hyperbaric oxygen therapy is particularly effective for severe carbon monoxide poisoning cases.

Ischemic hypoxia results from impaired or blocked blood circulation to tissues, preventing efficient oxygen delivery despite adequate oxygen availability in the blood. The stagnant blood flow means tissues cannot receive sufficient oxygen, even when hemoglobin is properly saturated. This type differs from other hypoxia forms because the problem is circulatory, not respiratory or cellular.

In histotoxic hypoxia, cells cannot efficiently utilize delivered oxygen due to metabolic poisons such as cyanide. These toxins interfere with cellular respiration mechanisms, preventing cells from extracting and using oxygen even when it is abundantly available. The oxygen supply reaches tissues normally, but cellular dysfunction prevents its utilization.

Hypoxemic hypoxia occurs when arterial oxygen pressure is reduced, caused by abnormal ventilation-perfusion coupling, pulmonary diseases affecting ventilation, or breathing air with low oxygen content. Carbon monoxide poisoning represents a special case of hypoxemic hypoxia. These conditions prevent adequate oxygen from entering the bloodstream in the first place.