CEREBRAL OXYGENATION DURING CARDIOPULMONARY BYPASS IN CHILDREN

Objective: Previous work has found cerebral oxygen extraction to decre ase during hypothermic cardiopulmonary bypass in children. To elucidat e cardiopulmonary bypass factors controlling cerebral oxygen extractio n, we examined the effect of perfusate temperature, pump bow rate, and hematocrit value on cerebral hemoglobin-oxygen saturation as measured by near infrared spectroscopy. Methods: Forty children less than 7 ye ars of age scheduled for cardiac operations with continuous cardiopulm onary bypass were randomly assigned to warm bypass, hypothermic bypass , hypothermic low-flow bypass, or hypothermic low-hematocrit bypass. F or warm bypass, arterial perfusate was 37 degrees C, hematocrit value 23%, and pump flow 150 ml/kg per minute. Hypothermic bypass differed f rom warm bypass only in initial perfusate temperature (22 degrees C); hypothermic low-flow bypass and low-hematocrit bypass differed from hy pothermic bypass only in pump flow (75 ml/kg per minute) and hematocri t value (16%), respectively. Cerebral oxygen saturation was recorded b efore bypass (baseline), during bypass, and for 15 minutes after bypas s had been discontinued. Results: In the warm bypass group, cerebral o xygen saturation remained at baseline levels during and after bypass. In the hypothermic bypass group, cerebral oxygen saturation increased 20% +/- 2% during bypass cooling (p < 0.001), returned to baseline dur ing bypass rewarming, and remained at baseline after bypass, In the hy pothermic low-flow and hypothermic low-hematocrit bypass groups, cereb ral oxygen saturation remained at baseline levels during bypass but in creased 6% +/- 2% (p = 0.05) and 10% +/- 2% (p < 0.03), respectively, after bypass was discontinued. Conclusions: In children, cortical oxyg en extraction is maintained during warm cardiopulmonary bypass at full flow and moderate hemodilution. Bypass cooling can decrease cortical oxygen extraction but requires a certain pump flow and hematocrit valu e to do so. Low-hematocrit hypothermic bypass and low-flow hypothermic bypass can also alter cortical oxygen extraction after discontinuatio n of cardiopulmonary bypass.