Systemic blood pressure and cerebral blood flow velocity during carotid surgery

Background: To evaluate the effect of mean arterial blood pressure (MAP) on cerebral perfusion during carotid surgery, we investigated blood flow velo city in the middle cerebral (Vs,mca) using transcranial Doppler ultrasonogr aphy (TCD). Methods: During carotid crossclamping, treatment included eithe r phenylephrine-induced hypertension without shunting (Group XC; n =11) or insertion of a shunt (Group S; n=12). Results: Increasing MAP in Group XC b efore crossclamping (81+/-13 mmHg to 107+/-112 mmHg) caused an increase of Vs,mca (59+/-17 cm/s to 75+/-20 cm/s; p <0.001). During crossclamping witho ut a shunt, Vs,mca was not dependent on MAP, and was reduced (mean 47+/-24 cm/s) in relation to preclamp values. In Group S, Vs,mca was always depende nt on MAP and the preclamp velocity was maintained (before shunt: 75+/-26cm /sec; during shunt: 79+/-30 cm/sec). Conclusions: Although we found an impa ired cerebral autoregulation, Vs,mca was independent of MAP during carotid crossclamping. Thus, TCD measurements have to be interpreted with caution d uring crossclamping, and the effect of induced hypertension has to be confi rmed with more invasive measures of cerebral blood flow.