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Cardiovascular effects of d-tubocurarine and pancuronium in newborn lambs during normoxic and hypoxia

Abstract:

Nondepolarizing muscle relaxants are administered to hypoxic neonates (including those with severe cyanotic congenital heart disease) to reduce oxygen consumption. However, it is unknown whether paralysis actually reduces oxygen consumption or whether the drugs used affect the cardiovascular system of neonates. Therefore, we studied the effects of d-tubocurarine and pancuronium induced muscle paralysis on oxygen consumption, cardiac output, and tissue oxygen delivery in healthy nor-moxic and hypoxic 1- to 3-day-old lambs. We measured intravascular pressures, cardiac output and its distribution (microspheres), and blood gases and pH during: 1) spontaneous respiration with room air (control); 2) spontaneous respiration with a Pao2 of 27-33 mm Hg (hypoxia); 3) mechanical ventilation with room air; 4) mechanical ventilation with room air and paralysis with d-tubocurarine (0.3 mg/kg) or pancuronium (0.1 mg/kg); and 5) mechanical ventilation with hypoxia and paralysis. Mechanical ventilation, with or without muscle paralysis, had no effect on the oxygen delivery or oxygen consumption of normoxic animals. Hypoxia and spontaneous ventilation had no effect on oxygen consumption, but hypoxia, paralysis, and mechanical ventilation reduced it 35% (p < 0.002 d-tubocurarine) and 50% (p < 0.001 pancuronium). Cardiac output was unaffected by oxygenation, mechanical ventilation, or muscle paralysis. However, blood flow to the brain and heart increased during hypoxia, which maintained normal oxygen delivery to these organs. During hypoxia and spontaneous ventilation, mean pulmonary arterial pressures increased 34% (d-tubocurarine) and 54% (pancuronium) above control; during hypoxia, muscle paralysis, and mechanical ventilation, it increased 81%. Myocardial blood flows and right ventricular rate-pressure products increased during hypoxia and were greatest during hypoxia, paralysis, and mechanical ventilation. Serum lactate levels increased 30-50% during hypoxia and spontaneous ventilation and remained elevated for the rest of the study. These data indicate that muscle paralysis and mechanical ventilation reduce the total body oxygen consumption of hypoxic lambs, but have no effect on the oxygen consumption of normoxic lambs. They also show that muscle paralysis increases the level of hypoxic pulmonary vasocon-striction, but that paralysis does not interfere with hypoxia induced bkp_redistribution of blood flow. We conclude that similar muscle relaxant induced changes may be beneficial to most hypoxic neonates, but that the pulmonary vascular effects, if similar to those found in our lambs, may be undesirable in neonates with pumonary vascular or right-sided heart disease. © 1986 International Pediatric Research Foundation, Inc.