CEREBRAL OXYGEN-SATURATION, TRANSCRANIAL DOPPLER ULTRASONOGRAPHY AND STUMP PRESSURE IN CAROTID SURGERY

Transcranial Doppler ultrasonography (TCD) of the middle cerebral arte ry (MCA), light-reflective cerebral oximetry and measurement of intern al carotid artery stump pressure were compared as methods of monitorin g cerebral perfusion during carotid surgery in 33 patients. Median cer ebral oxygen saturation was 70 (range 62-85) per cent and TCD-measured mean blood velocity 42 (range 19-91) cm/s before carotid cross-clampi ng, falling to 68 (53-83) per cent and 16 (0-50) cm/s respectively on application of the clamps (P < 0.001). Stump pressure correlated close ly with MCA blood velocity 30 s after the start of cross-clamping (r(S ) = 0.58, P < 0.001), but not with cerebral oxygen saturation. A fall of 5 per cent or more in cerebral oxygen saturation following cross-cl amp application was predicted by a decrease in mean MCA blood velocity of at least 60 per cent. Changes in cerebral oxygen saturation correl ated significantly with systolic blood pressure throughout the periope rative period (r(S) = 0.41, P < 0.001). Significant falls in cerebral oxygenation were not predicted by low stump pressure but were associat ed with large reductions in the mean MCA blood velocity measured by TC D.