Lactic acid changes during and after hypothermic cardiopulmonary bypass in infants

Infants undergoing open-heart surgery with hypothermic cardiopulmonary bypass experience markedly elevated lactate and glucose levels. Reports in infants less than 10 kg show the elevated lactate to be progressive during the operative period. The pathogenesis of the hyperglycemia is not clear but may be caused by excess glucose administration, inadequate insulin response, or glucose regulatory hormone levels of glucagon, cortisol, and growth hormone. The purpose of this study is to confirm these findings and to investigate their pathogenesis. Serial blood samples were taken preoperatively, intraoperatively, and postoperatively during hypothermic cardiopulmonary bypass in nine infants of less than 10 kg. Samples were analyzed for levels of lactate, glucose, and regulatory hormones insulin, growth hormone, glucagon, and cortisol. Our study did not show a progressive accumulation of lactate. The elevated lactate level appears to come from the pump prime solution. The hyperglycemia is also from the pump prime solution, and there do not appear to be elevated levels of regulatory hormones intraoperatively. Insulin response during hypothermia is blunted; however, on rewarming the patient in the immediate postoperative period, a brisk insulin response is seen. The changes in levels of lactate and glucose and the regulatory hormones return to baseline at 24 hours with no further significant changes in the next 48 hours.