Moderate Hypothermia with Low Flow Rate Cardiopulmonary Bypass in Congenital Heart Defect Surgery

Abstract

Low flow rate perfusion has been recommended in profound hypothemric cardiopulmonary bypass (CPB) in recent years, but has not been used in moderate hypothermic CPB. In this report, 30 patients with congenital heart defects, from 2 to 11 years old and weighing 11.5 to 25 kg. were selected to be the subjects of moderate hypothermia with low flow rate perfusion. Once on CPB, a high flow rate of 2.27 ± 0.36 L/min/m2 was used to cool the patient to 25.6 ± 0.84°C rectal, 24.1 ± 1.32°C esophageal, and 23.8 ± 1.4°C tympanic temperature, followed by a low flow rate of 1.23 ± 0.09 Llmin/m2 until the main intracardiac repair was completed. Rewarming to a rectal temperature of 34.5–35.0°C was accomplished with a high flow rate of 2.70 ± 0.22 L/min/m2 until weaning. The total CPB, cross clamp, and low flow rate perfusion times were 95.4 ± 34.6 min, 51.4 ± 20.2 min, and 45.7 ± 22.4 min respectively. A second group of five patients from 1.5 to 4 years old and from 6 to 11 kg were operated on with profound hypothermic circulatory arrest. A high flow rate of 2.35 ± 0.43 L/min/m2 was used to cool the temperature to 19.3 ± 0.8°C rectal, 17.5 ± 2.2°C esophageal, and 17.8 ± 1.5°C tympanic, and then the circulation was temporarily arrested. The CPB and arrest time were 55.0 ± 10.7 min and 44.7 ± 3.8 min respectively. Among the patients under moderate hyperthermia with low flow rate perfusion, only one showed metabolic acidosis during cardiopulmonary bypass and received an extra 12 mEq sodium bicarbonate. After 27 to 99 min low flow rate perfusion. the venous oxygen saturation was still greater than 80% for each patient and lactate concentration did not increase. In contrast, among those cases using profound hypothermic circulatory arrest, the blood gas analysis after two min of rewarming demonstrated an obvious metabolic acidosis and increase in lactate concentration. An extra 9 to 24 mEq sodium bicarbonate was needed in each of five patients for acidosis correction. After the sodium bicarbonate administration, the blood gases returned to normal while the lactate concentration still increased progressively. The data from this study suggest that low flow rate perfusion may safely be used in moderate hyperthermic CPB as long as we monitor the oxygen saturation of returned venous blood, keeping it above 80%.