Hyperventilation after tourniquet deflation prevents an increase in cerebral blood flow velocity

Abstract

Purpose: In this study we examined whether normocapnia maintained by hyperventilation after lower limb tourniquet deflation prevents an increase in cerebral blood flow velocity. Methods: Thirteen patients, undergoing elective orthopedic surgery, requiring a pneumatic tourniquet around the lower extremity, were divided into two groups. In group I, ventilation was controlled at tidal volume of 10 mL·kg-1 and respiratory rate of eight per minute after tourniquet release. In group 2, ventilation was controlled to maintain P(ET)CO2 between 30 and 35 mmHg after tourniquet release. Arterial blood pressure, heart rate, peak and mean middle cerebral artery (MCA) flow velocity, and arterial blood gas were measured every minute for ten minutes after tourniquet release. The MCA blood flow velocity was measured using Transcranial Doppler ultrasonography (TCD). Results: In group I, the maximum peak MCA flow velocity was 53 ± 6 cm·sec-1 (50 % ± 6% increase compared with pre- release value), and achieved 3 ± 0.4 min after tourniquet release. In group 2, there was no increase either in mean or peak MCA velocity after tourniquet release. Conclusions: Normocapnia maintained by hyperventilation after tourniquet deflation prevents an increase in cerebral blood flow velocity.