Cerebral blood flow velocity in pediatric patients is reduced after cardiopulmonary bypass with profound hypothermia.

Transcranial Doppler sonography of the middle cerebral artery was used to determine whether cerebral perfusion was detectable in low flow states during operations with cardiopulmonary bypass in pediatric patients. Quantitative and qualitative differences in cerebral blood flow velocity after rewarming in patients treated with continuous low-flow bypass or deep hypothermic circulatory arrest were assessed. To determine whether the alterations in cerebrovascular resistance pattern observed in our patients undergoing profound hypothermia was more a function of perfusion technique than of minimum temperature during operation, a third group of patients treated with moderate hypothermia was studied. The three patient groups were the arrest group (N = 16), comprised of patients undergoing circulatory arrest at 18 degrees to 20 degrees C; the low-flow group (N = 16), patients treated with continuous low-flow (cardiac index 0.5 L/min per square meter) bypass at 18 degrees to 20 degrees C; and the moderate group (N = 5), patients treated with moderate hypothermia at 24 degrees to 28 degrees C. Flow velocity was detectable in all patients in the low-flow group, with mean arterial pressures as low as 15 mm Hg. Mean flow velocity was reduced after bypass as compared with prebypass values in both the arrest and low-flow groups (p = 0.0001). Mean flow velocity increased after bypass in the moderate group (p = 0.0001). A Doppler waveform pattern consistent with high cerebrovascular resistance was found in 67% of patients in the arrest group and 44% of those in the low-flow group. None of the patients in the moderate group exhibited such a pattern. Patients treated with profound hypothermia who underwent a period of cold full-flow reperfusion before rewarming did not exhibit this high resistance pattern after rewarming. The present findings indicate that profound hypothermia may evoke changes in the cerebral vasculature that result in decreased mean cerebral blood flow velocity after cardiopulmonary bypass rewarming. A period of cold full-flow reperfusion before rewarming may prevent these alterations and improve cerebral perfusion during rewarming.