hypoxia /hīpok″sē·ə/ [Gk, hypo + oxys, sharp, genein, to produce] , inadequate oxygen tension at the cellular level, characterized by tachycardia, hypertension, peripheral vasoconstriction, dizziness, and mental confusion. Mild hypoxia stimulates peripheral chemoreceptors to increase heart and respiration rates. The central mechanisms that regulate breathing fail in severe hypoxia, leading to irregular respiration, Cheyne-Stokes respiration, apnea, and respiratory and cardiac failure. Increased sensitivity to the depressant effect of opiates on the respiratory system is common in chronic hypoxia, causing severe depression of respiration or apnea from relatively small doses. If the availability of oxygen is inadequate for aerobic cellular metabolism, energy is provided by less efficient anaerobic pathways that produce metabolites other than carbon dioxide and water. The tissues most sensitive to hypoxia are the brain, heart, pulmonary vessels, and liver. Treatment may include cardiotonic and respiratory stimulant drugs, oxygen therapy, mechanical ventilation, and frequent analysis of blood gases. Compare hypoxemia. See also acute hypoxia, anoxia, chemoreceptor, chronic hypoxia, hyperventilation, respiratory center. −hypoxic, adj.
