CEREBROVASCULAR STABILITY DURING ISOFLURANE ANESTHESIA IN CHILDREN

The aims of this study were firstly, to determine the effect of various concentrations of isoflurane on cerebrovascular circulation and secondly, to examine the time-response characteristics of the drug on cerebral blood flow velocity in anaesthetized children. Thirty-two ASA physical status I or II patients aged one to eight years and scheduled for urological surgery were studied. Anaesthesia was induced with thiopentone 5 mg.kg-1 and fentanyl 2-mu-g.kg-1. Muscle relaxation was provided with vercuronium 0.1 mg.kg-1. Tracheal intubation was performed in all cases. Anaesthesia was maintained with isoflurane in a mixture of air and oxygen to produce an inspired oxygen fraction (FIO2) of 0.3. Ventilation was adjusted to maintain normocapnia. A caudal or lumbar epidural catheter was inserted before skin incision and a continuous bupivacaine, without epinephrine, infusion established. During the first part of this study, the initial isoflurane concentration for 24 patients was randomized and age-adjusted to 0.5 MAC, 1.0 MAC, or 1.5 MAC. After steady-state was reached, the subsequent isoflurane MAC concentration was randomized by either raising or lowering it from the initial concentration. In the second part of this study, the time-response effect of isoflurane was examined. Eight patients received 1.0 MAC isoflurane over 90 to 150 min. Temperature, heart rate, and systolic blood pressure were unchanged throughout the study. Cerebral blood flow velocity (CBFV) and resistance index (RI+), a measure of cerebrovascular resistance, were measured in the M1 segment of the middle cerebral artery (MCA) with a 2 MHz transcranial Doppler monitor. The CBFV and RI+ did not change when the initial isoflurane MAC concentration of either 0.5, 1.0, or 1.5 MAC, was varied. Furthermore, there was no change in CBFV and RI+ when isoflurane was administered over time. This indicates that varying isoflurane MAC concentrations between 0.5 MAC and 1.5 MAC did not have any effect on cerebral circulation and that the administration of a constant concentration of isoflurane over time does not affect cerebral haemodynamic variables in anaesthetized healthy children.