Henderson J M, Nathan H J, Lalande M, Winkler M H, Dubé L M
Department of Anaesthesia, University of Ottawa Heart Institute, Ottawa Civic Hospital, Ontario.
Can J Anaesth. 1988 Nov;35(6):587-90. doi: 10.1007/BF03020345.
To help decide when an inhalational agent should be discontinued during cardiopulmonary bypass (CPB), its rate of washin and washout must be known. Isoflurane one per cent was administered to 14 patients undergoing CPB and isoflurane blood concentrations were measured to determine the time course of washin and washout of this agent. Bubble oxygenators were used for seven patients and membrane oxygenators for the remaining seven. During the administration of isoflurane, isoflurane blood concentrations rose slowly and did not reach a steady state during the time available for washin. Isoflurane blood concentrations decreased by at least 50 per cent within two minutes of turning off the vaporizer, and by 15 minutes the concentration had dropped by 75 per cent. There was a tendency for more rapid elimination of isoflurane in patients undergoing rewarming during this period. There did not appear to be an important difference between bubble and membrane oxygenators in the rate of washin and washout of isoflurane. Within 15 minutes of turning off the vaporizer only 25 per cent of the original blood concentration of isoflurane will remain. The anaesthetist must decide what concentration of isoflurane is acceptable during separation from CPB. Knowledge of the time course of isoflurane washout will allow more accurate determination of when to discontinue its administration in order to reach an acceptable concentration by the time separation from CPB occurs.
为了帮助确定在体外循环（CPB）期间何时应停用吸入性麻醉剂，必须了解其吸入和清除速率。对14例接受CPB的患者给予1%异氟烷，并测量异氟烷血药浓度，以确定该药物的吸入和清除时间过程。7例患者使用鼓泡式氧合器，其余7例使用膜式氧合器。在给予异氟烷期间，异氟烷血药浓度上升缓慢，在吸入时间内未达到稳态。关闭蒸发器后两分钟内，异氟烷血药浓度至少降低50%，15分钟时浓度下降75%。在此期间正在复温的患者中，异氟烷的清除有加快的趋势。在异氟烷的吸入和清除速率方面，鼓泡式氧合器和膜式氧合器之间似乎没有重要差异。关闭蒸发器15分钟内，异氟烷的血药浓度仅会保留原始浓度的25%。麻醉医生必须确定在脱离CPB期间可接受的异氟烷浓度。了解异氟烷清除的时间过程将有助于更准确地确定何时停止给药，以便在脱离CPB时达到可接受的浓度。
