Abstract
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 μg · 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 MI 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.
Résumé
La présente étude a pour but d’identifier l’effet de différentes concentrations d’isoflurane ainsi qu’examiner l’effet de la durée d’administration sur la circulation cérébrovasculaire de 32 enfants, âgés de un á huit ans, ASA I ou II, et anesthésie pour interventions urologiques. L’induction de l’anesthésie a été pratiquée à l’aide de thiopentone 5,0 mg · kg−1 et de fentanyl 2,0 μg · kg−1. La relaxation musculaire était assurée à l’aide de vécuronium 0,1 mg · kg−1 et la trachée intubée. Le maintien de l’anesthésie a été assuré à l’aide d’isoflurane dans un mélange d’air et d’oxygène de façon à produire une fraction inspirée d’oxygène (FiO2) de 0,3. La ventilation mécanique était ajustée pour maintenir la normocapnie. Un bloc caudal ou un bloc lombaire épidural continu était administré avant le début de la chirurgie. Durant la première partie de cette étude, la concentration initiale d’isoflurane de 24 patients était ajustée de façon aléatoire, à 0,5,1,0 ou 1,5 MAC, au tenant compte de la correction pour l’âge. Après avoir atteint l’état d’équilibre, la concentration d’isoflurane suivante était administrée, au hasard, d’une façon croissante ou décroisante par rapport à la concentration initiale. Durant la deuxième partie, nous avons examiné l’effet du temps sur l’administration continue de 1,0 MAC d’isoflurane chez huit patients anesthésiés pour une durée de 90 à 150 minutes. La pression artérielle systolique, le rythme cardiaque et la température sont demeurés inchangés durant toute la période étudiée. La vélocité du débit sanguin cérébral (CBFV) ainsi que l’index de résistance cérébrovasculaire (RI+) de l’artère cérébrale moyenne (MCA) ont été mesurés avec l’aide d’un moniteur Doppler transcranien utilisant une fréquence de 2 MHz. La CBFV et le RI + n’ont pas changé lorsque la concentration initiale d’isoflurane (0,5, 1,0, ou 1,5 MAC), était augmentée ou diminuée pour compléter la boucle. De plus, nous n’avons pas observé de changement de la CBFV et du RI+ lorsque l’isoflurane était administré pour une longue période de temps. Ces résultats démontrent que les différentes concentrations d’isoflurane n’affectent pas la circulation cérébrovasculaire et que la durée d’administration d’une concentration fixe d’isoflurane ne modifie pas certaines des variables hémo-dynamiques cérébrales lors de l’anesthésie chez des enfants sains.
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Bisonnette, B., Leon, J.E. Cerebrovascular stability during isoflurane anaesthesia in children. Can J Anaesth 39, 128–134 (1992). https://doi.org/10.1007/BF03008642
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DOI: https://doi.org/10.1007/BF03008642