Absent diastolic cerebral blood flow velocity after circulatory arrest but not after low flow in infants.

It is controversial whether profound hypothermia (15 degrees C) provides adequate cerebral protection during a limited period of total circulatory arrest during pediatric cardiac surgery. In the present study, transcranial Doppler echography was used to monitor the blood flow velocity (BFV) pattern in the middle cerebral artery (MCA). The purpose of the study was to investigate the influence of a period of circulatory arrest on MCA BFV, as judged from the reperfusion flow velocity pattern. The MCA BFV was studied in 22 small children undergoing profound hypothermic cardiac operations after induction of anesthesia. Twelve of the children had a period of profound hypothermic circulatory arrest (15 to 74 minutes; arrest group). Circulation was maintained in the remaining 10 children (nonarrest group). Time-averaged MCA BFV was decreased and diastolic BFV was absent immediately after cardiopulmonary bypass in 10 of 12 children in the arrest group. In contrast, only 1 of 10 patients in the nonarrest group (p < 0.05) showed this pattern. Diastolic BFV normalized 54 to 328 minutes after the arrest in the arrest group. Circulatory arrest during profound hypothermia is followed by a period of low cerebral perfusion, whereby time-averaged MCA BFV is decreased and MCA BFV is absent during diastole. We speculate that this can be explained by an increase in intracranial pressure after brain edema.