Blood flow velocity in the middle cerebral artery response to tourniquet release.

This study was undertaken to examine the effects of tourniquet release on middle cerebral arterial (MCA) blood flow velocity in patients undergoing general anaesthesia for orthopaedic surgery. In 30 patients (ASA physical status 1 or 2) undergoing orthopaedic procedures on the upper (Group U, n = 15) and lower (Group L, n = 15) extremities, MCA blood flow velocity was measured before and after tourniquet deflation using transcranial Doppler sonography. The MCA blood flow velocity increased after release of the intraoperative tourniquet and remained elevated for two minutes in Group U (P < 0.05) and for four minutes in Group L (P < 0.05). The increase in MCA blood flow velocity was greater in Group L than in Group U (P < 0.05). A positive linear correlation between MCA blood flow velocity and PETCO2 after tourniquet deflation was observed in both groups (P < 0.001).