• Hong Yang, H Mayumi Homi, Betty E Smith, and Hilary P Grocott.
• Department of Anesthesiology (Multidisciplinary Neuroprotection Laboratories), Duke University Medical Center, Durham, NC, USA.
• J. Cardiothorac. Vasc. Anesth. 2004 Oct 1; 18 (5): 620-3.

ObjectiveThe purpose of this investigation was to determine the influence of cardiopulmonary bypass (CPB) on the minimum alveolar concentration (MAC) of isoflurane in a rat model of CPB.DesignProspective.SettingUniversity research laboratory.ParticipantsSprague-Dawley rats.InterventionsUsing tail-clamp methodology, the pre- and post-CPB MAC for isoflurane was studied.Methods And Main ResultsRats were anesthetized with isoflurane, intubated, ventilated, and surgically prepared for CPB, after which they were randomized to either Sham-operated or CPB groups. The CPB group (n = 10) underwent 90 minutes of normothermic nonpulsatile CPB. The Sham group (n = 13) were cannulated but did not undergo CPB. Pre- and post-CPB MAC determinations were compared within groups using a paired Student t test. The CPB group had a pre-CPB baseline isoflurane MAC of 1.09% +/- 0.11% versus 1.09% +/- 0.08% in the Sham group (p = 0.90). Twenty minutes after CPB, the CPB group exhibited a decrease in MAC to 0.98% +/- 0.14% (p = 0.0026, compared with baseline). The MAC in the Sham group was unchanged (p = 0.5852, compared with baseline). Two hours after CPB, the MAC in the CPB group remained lower compared with baseline at 0.99% +/- 0.14% (p = 0.0032).ConclusionsCPB resulted in a small (10%) but significant reduction in the MAC for isoflurane. The mechanism behind this reduction in MAC is not clear but may be related to CPB-induced cerebral injury.

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