Influence of aortic blood flow velocity on changes of middle cerebral artery blood flow velocity during isoflurane and sevoflurane anaesthesia

Background and objective We studied the influence of systemic (aortic) bloo d flow velocity on changes of cerebral blood flow velocity under isoflurane or sevoflurane anaesthesia. Methods Forty patients (age: isoflurane 24-62 years; sevoflurane 24-61 year s; ASA I-III) requiring general anaesthesia undergoing routine spinal surge ry were randomly assigned to either group. Cerebral blood flow velocity was measured in the middle cerebral artery by transcranial Doppler sonography (depth: 50-60 mm). Systemic blood flow velocity was determined by transthor acic Doppler sonography at the aortic valve. Heart rate, arterial pressure, arterial oxygen saturation and body temperature were monitored. After stan dardized anaesthesia induction (propofol, remifentanil, vecuronium) sevoflu rane or isoflurane were used as single agent anaesthetics. Cerebral blood f low velocity and systemic blood flow velocity were measured in the awake pa tient (baseline) and repeated 5 min after reaching a steady state of inspir atory and end-expiratory concentrations of 0.75, 1.00, and 1.25 mean alveol ar concentrations of either anaesthetic. To calculate the influence of syst emic blood flow velocity on cerebral blood flow velocity, we defined the ce rebral-systemic blood flow velocity index (CSvl). CSvl of 100% indicates a 1:1 relationship of changes of cerebral blood flow velocity and systemic bl ood flow velocity. Results Isoflurane and sevoflurane reduced both cerebral blood flow velocit y and systemic blood flow velocity. The CSvl decreased significantly at all three concentrations vs, 100% (jsoflurane/sevoflurane: 0.75 MAC: 85 +/- 25 %/81 +/- 23%, 1.0 MAC: 79 +/- 19%/74 +/- 16%, 1.25 MAC: 71 +/- 16%/79 +/- 2 1%; [mean +/-SD] P = 0.0001). Conclusions The reduction of the CSvl vs. 100% indicates a direct reduction of cerebral blood flow velocity caused by isoflurane/sevoflurane, independ ently of systemic blood flow velocity.