Comparative study of noninvasive cerebrovascular monitoring methods in cardiac surgery.

Unfavorable incidents during cardiac operations due to inadequate cerebral perfusion can be avoided by the utilization of noninvasive blood flow monitoring methods. The purpose of this study was to evaluate monitoring systems for cebrovascular perfusion. We compared currently available blood flow monitoring devices including transcranial Doppler (TCD), central retinal artery color Doppler (CRAD) and near-infrared spectroscopy (NIRS). The maximum flow velocity (Vmax) of the right central retinal artery was measured with a 7.5 MHz Doppler system. The Vmax of the right middle cerebral artery was measured with a TCD system. Regional tissue oxygen saturation (rSO2) was continuously measured with a NIRS system. The total number of individual data for each monitoring method collected from 25 patients was 184. The CRAD-Vmax was correlated more closely with the corresponding maximum blood pressure than the TCD-Vmax (r = 0.742 and 0.607, respectively). No missing data were seen in CRAD, but 20 missing data were seen in TCD, mostly during the period of cardiopulmonary bypass with lowered blood pressure. All 184 data were divided into two groups: Group 1 (rSO2 > or = 60 %, n=175) and Group 2 (rSO2 <60 %, n=9 data). The CRAD-Vmax was significantly lower in Group 2 (5.2+/-2.4 cm/s versus 3.0+/-0.4 cm/s, p<0.001). However, there was no significant difference in the TCD-Vmax between these two groups. Thus, CRAD may be superior to TCD in detecting insufficiency of cerebral blood flow correlating to rSO2, and could be used as the first choice monitoring system of cerebral blood flow during cardiac surgery.