Cerebral blood flow velocity patterns during cardiac surgery utilizing profound hypothermia with low-flow cardiopulmonary bypass or circulatory arrest in neonates and infants.

To examine the effects of low-flow cardiopulmonary bypass (CPB) and circulatory arrest (PHCA) on cerebral pressure-flow velocity relationships, we studied 32 patients (< 9 mo of age) undergoing corrective cardiac procedures. Pressure-flow velocity relationships were studied during profound hypothermia (nasopharyngeal temperature < 20 degrees C). Cerebral blood-flow velocity (CBFV) was measured in the middle cerebral artery using transcranial Doppler sonography. The anterior fontanel pressure (AFP) was measured using an intracranial pressure monitor. Cerebral perfusion pressure (CPP) was calculated (mmHg) as mean arterial pressure (MAP) minus AFP. Nasopharyngeal temperature, PaCO2 and haematocrit were controlled during the study period. Alpha-stat acid-base management was employed. The CBFV measurements were made continuously over a range of CPP as pump flow (Q) was decreased to low-flow or to circulatory arrest and again during the subsequent increase in Q and CPP to normal. As Q and CPP were increased after a period of low-flow CPB during which period detectable CBFV was present, the CBFV was greater at any given CPP than prior to the low-flow state (P < 0.05). However, after PHCA a higher CPP (P < 0.05) was necessary to re-establish detectable CBFV and at any given CPP the CBFV was less than prior to PHCA (P < 0.05). Seventeen patients underwent low-flow CPB during which CBFV became non-detectable (7 +/- 1 cm.sec-1). In 12 of these patients the pattern of recovery of CBFV was the same as that observed after low-flow CPB whereas the remaining five (29%) demonstrated a pattern of recovery identical to the ones recorded after PHCA. We conclude that after PHCA a higher CPP is necessary to re-establish and maintain detectable CBFV. Furthermore, during low-flow CPB, patients where CBFV becomes non-detectable and show a pattern of CBFV recovery similar to PHCA, cessation of cerebral perfusion must be considered.