Moderate hypothermia with low flow rate cardiopulmonary bypass used in surgeries for congenital heart defects.

Low flow rate perfusion has been recommended in profound hypothermic cardiopulmonary bypass (CPB) in recent years. However, most patients with congenital heart defects are still operated on under moderate hypothermic CPB, where high flow rate perfusion has been adopted by most perfusionists. Fifty patients with congenital heart defects, ranging from 1 to 11 yr of age and 6.5 to 25 kg of weight, were included in the trial. Once on CPB, a high flow rate of 2.37 +/- 0.39 L/min/m was used to cool the patient to 27.3 degrees C +/- 0.84 degrees C rectal temperature, followed by a low flow rate of 1.31 +/- 0.09 L/min/m until the main intracardiac repair was completed and rewarming started. High flow rate was still used in rewarming the patients to a rectal temperature of 35 degrees C-36 degrees C. The total CPB, cross-clamp, and low flow rate perfusion time were 86.4 +/- 26.6, 46.4 +/- 22.3, and 40.7 +/- 22.4 min, respectively. After 24-99 min low flow rate perfusion, venous oxygen saturation remained above 80% for all the patients, and lactate concentration did not increase. Only three patients showed slight metabolic acidosis during CPB and required an extra 6-12 mEq sodium bicarbonate. Average urine output was 199 +/- 155 (50-600) ml during CPB. All patients recovered well after operation. No surgical death or neurologic complications occurred. Low flow rate perfusion might be safely used in moderate hypothermic CPB as long as the oxygen saturation of returned venous blood was kept above 80%.