Introduction: Because of the reports of improved myocardial performance, cardiopulmonary bypass (CPB) with systemic normothermia is being increasingly used in many institutions recently . During hypothermic CPB anaesthetic requirements are reduced by hypothermia itself . However, during normothermic CPB, anaesthetic requirements should not be changed, thus the anaesthetic requirements may be higher than that during hypothermic CPB. To investigate the difference in anaesthetic requirements, we performed a prospective, randomized study of bispectral index (BIS) changes in patients with either normothermic or hypothermic CPB.
Method: Patients scheduled for elective coronary artery bypass graft surgery were randomly allocated to a normothermic group (GN; n = 20) or hypothermic group (GH; n = 20). Anaesthesia was maintained with isoflurane (0.5-1.2% volume) and supplemented with fentanyl (0.1-0.3 μg kg−1 min−1). The fentanyl infusion rate and the concentration of isoflurane were not changed from the period 15 min before starting CPB and throughout CPB. In GH, hypothermia was induced with a target rectal temperature of 30°C. The anaesthesiologist in charge was blinded to BIS. Change in BIS, mean arterial pressure (MAP), and nasopharyngeal temperature were recorded at the following times: (1) pre-CPB; after induction when vital signs were stable, (2) CPB 10; 10 min after start of CPB, (3) CPB 60; 60 min after start of CPB, (4) CPB off; 30 min after weaning from CPB.
Results: There was no difference in patients' demographic data, duration of CPB or MAP nor in isoflurane concentration or fentanyl requirement between the two groups. In the follow-up, no patients could recall anything from the operation.
Discussion: During CPB, GN showed higher BIS values than GH. Our results suggest that during normothermic CPB, anaesthetic requirements may be greater than that of hypothermic CPB.
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2 Vitez TS, White PF, Eger EI. Effects of hypothermia on halothane MAC and isoflurane MAC in the rat. Anesthesiology