Changes in blood flow velocity in the middle cerebral artery during nonpulsatile hypothermic cardiopulmonary bypass.
OBJECTIVE
We evaluated the utility of blood flow velocity measurements by transcranial Doppler ultrasonography 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 original 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 nasopharyngeal 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.
Endoh
H
H
Department of Anesthesiology, Niigata City General Hospital, Japan.
Shimoji
K
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D002315:Cardiopulmonary Bypass; D002536:Cerebral Arteries / Q000503:physiopathology*; D001026:Coronary Artery Bypass; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D009131:Muscle, Smooth, Vascular / Q000503:physiopathology; D010101:Oxygen Consumption; D011674:Pulse