Changes in Blood Flow Velocity in the Middle Cerebral Artery During Nonpulsatile Hypothermic Cardiopulmonary Bypass

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Abstract

Background and Purpose

We evaluated the utility of blood flow velocity measurements by transcranial Doppler ultraso-nography as a tool to indirectly measure cerebral perfusion during cardiopulmonary bypass.

Methods

We simultaneously measured blood flow velocity in the middle cerebral artery and physiological variables in 18 patients undergoing cardiac surgery under hypothermic cardiopulmonary bypass in which pH and PaCO2 were managed with the alpha-stat acid-base strategy. We expressed blood flow velocity as a relative value of control obtained under normothermia and normocarbia before bypass. We also developed an orginal index, modified cerebral metabolic rate for oxygen, to estimate cerebral metabolic rate for oxygen.

Results

Relative velocity was significantly (P <.01) reduced during stable aortic cross-clamp compared with before bypass and was significantly (P<.01) increased during rewarming compared with at aortic cross-clamp. Modified cerebral metabolic rate for oxygen significantly correlated with nasopha-ryngeal temperature during cooling, aortic cross-clamp, and rewarming (r=.756, P<.0001; r=.4, P<.01;r=.725, P<.0005, respectively). Calculated temperature coefficient for modified cerebral metabolic rate of oxygen was 2.7 $$1.4 (mean$$SD, n=10) during cooling. Only nasopharyngeal temperature and PaCO2 were significant determinants of relative velocity during aortic cross-clamp.

Conclusions

We can monitor cerebral perfusion and metabolism by measurements of relative velocity and modified cerebral metabolic rate for oxygen during hypothermic cardiopulmonary bypass. (Stroke. 1994;25:403-407.)

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