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The cardiovascular and metabolic effects of halothane in normoxic and hypoxic newborn lambs

Abstract:

Oxygen consumption, cardiac output, and tissue oxygen delivery were measured in normoxic and hypoxic 1-3-day-old lambs during the following six conditions: 1) (control) paralysis with pancuronium and controlled ventilation with room air; 2) paralysis, controlled ventilation and hypoxia (Pa(O2) = 30 ± 3 mmHg, [SD]; 3) paralysis, controlled ventilation with room air and 0.5 MAC halothane; 4) paralysis, controlled ventilation, hypoxia and 0.5 MAC halothane; 5) paralysis, controlled ventilation, hypoxia, and 1 MAC halothane; and 6) paralysis, controlled ventilation, hypoxia, and 1 MAC halothane. During normoxia, 0.5 and 1 MAC halothane decreased total body oxygen consumption, cardiac output, and arterial blood pressure. One-half MAC halothane had no effect on blood flow to any organ except muscle, whose flow decreased 64%. One MAC halothane decreased blood flow to the brain, heart, kidney, muscle, and gut. Both concentrations of halothane decreased serum catecholamine levels below control values and prevented hypoxia from increasing catecholamine levels. Hypoxia decreased the oxygen consumption about 40% from the immediately previous normoxic value, whether the animals were anesthetized or not. Tissue oxygen delivery followed changes in blood flow. The cardiac output, arterial blood pressure, and heart rate of anesthetized, hypoxic animals were not different from those in the previous normoxic condition. Halothane did not prevent bkp_redistribution of blood flow to the heart and brain of hypoxic animals, nor did halothane prevent hypoxic pulmonary vasoconstriction. Halothane did prevent the increase in serum catecholamine levels that occurs in unanesthetized, hypoxic animals. If halothane has similar effects in humans, it may be useful in treating hypoxic infants in the operating room and intensive care unit.