Alpha-Stat versus pH-Stat: Implications for the Brain During Cardiopulmonary Bypass

During cardiac surgery, systemic hypothermia is often utilized to augment cardioplegic myocardial preservation. The ensuing reduction in metabolic activity is directly related to the decrease in temperature as predicted by Vant Hoff's law. Lowered metabolic-activity decreases oxygen utilization, thus increasing tissue tolerance for reductions in oxygen delivery. Among numerous other physiologic effects, hypothermia increases the solubility of O2 and CO2 in blood, producing a fall in gaseous partial pressures, while total gas content remains unchanged. When this occurs with CO2, the corresponding rise in pH may be perceived as a "respiratory alkalosis.

Cerebral Blood Flow During Cardiopulmonary Bypass

This article reviews the development of cerebral blood flow techniques as used both clinically and experimentally formeasurementofcerebralbloodflow(CBF)andcerebral metabolic rate for oxygen (CMRO2) during cardiopulmonary bypass (CPB). The limitations associated with the various techniques for measurement of CBF during cardiopulmonary bypass are discussed, as well as considering the influence of some of the management options, including pH management and use of pulsatile or non pulsatile perfusion, on CBF and CMRO2 The impact of various perfusion techniques on neurological outcome following cardiopulmonary bypass is also considered