EFFECT OF PUMP FLOW-RATE ON CEREBRAL BLOOD-FLOW DURING HYPOTHERMIC CARDIOPULMONARY BYPASS IN ADULTS

Objective: The purpose of this study was to examine the effect of card iopulmonary bypass flow rate on cerebral blood flow and cerebral metab olic rate for oxygen during hypothermic (27 degrees C) cardiopulmonary bypass. Design, Setting, and Participants: The investigation was a pr ospective, randomized study in a tertiary care hospital setting. The 3 0 participants were volunteer adult cardiac surgical patients at a sin gle institution. Interventions: The N2O saturation method of Kety and Schmidt was used to determine global cerebral blood flow and metabolic rate during four periods: prebypass, cardiopulmonary bypass (CPB) (27 degrees C) flow rates of 2.3 and 1.2 L/min/m(2), and 30 minutes post- CPB. Anesthesia consisted of fentanyl and midazolam; pH management was alpha-stat, and mean arterial pressure was maintained at 50 to 70 mmH g throughout CPB. Measurements and Main Results: In the context of an unchanged mean arterial pressure, the pump flow did not affect cerebra l blood flow or metabolic rate during hypothermic CPB. Systemic venous oxygen saturation was also maintained during reduced flow at 27 degre es C. Hemodilution during hypothermic CPB maintained cerebral blood fl ow at prebypass levers. In the postbypass period, persistent hemodilut ion resulted in an elevated cerebral blood flow. Conclusions: Brain ox ygenation is well maintained at low than conventional pump flow levels during CPB. There may be practical advantages to reduced flows during hypothermia, and flow reductions do not appear to adversely affect ce rebral blood flow or metabolism. Copyright (C) 1997 by W.B. Saunders C ompany.