Propofol requirement titrated to bispectral index: a comparison between hypothermic and normothermic cardiopulmonary bypass

Abstract

Though propofol requirement is expected to decrease during cardiopulmonary bypass (CPB), a few studies have failed to demonstrate this. The factors affecting pharmacokinetics of propofol and, therefore, the requirement, are different during hypothermic and normothermic CPB. We evaluated and compared the requirement of propofol during hypothermic and normothermic CPB. Fifty adult patients scheduled for elective cardiac surgery on CPB were recruited and randomly allocated into hypothermic CPB (28-30 degrees C) (Group H) and normothermic CPB (35-37 degrees C) (Group N) groups. Patients were induced and maintained with propofol titrated to maintain a target bispectral index (BIS) of 50 +/- 10. Propofol requirement (mean +/- SD) was similar in normothermic and hypothermic groups, both before CPB (4.9 +/- 1.5 mg kg(-1)hr(-1) in Group N, 4.6 +/- 1.5 mg kg(-1)hr(-1) in Group H) and after cessation of bypass (p > 0.05) (4.6 +/- 1.8 mg kg(-1)hr(-1) in Group N and 4.3 +/- 1.7 mg kg(-1)hr(-1) in Group H). CPB significantly reduced (p < 0.001) propofol requirements in both arms of the study (Group N: 2.9 +/- 1.4 mg kg(-1)hr(-1)and Group H: 1.3 +/- 0.7 mg kg(-1)hr(-1)). This reduction was more pronounced in the hypothermic group (p < 0.001). The BIS (median +/- inter quartile range) remained constant during normothermic CPB (50 +/- 8.8), but declined significantly during hypothermic CPB (41 +/- 5.6) despite decreased usage of propofol during hypothermia. No patient had recall of intra-operative events. CPB decreases the magnitude of propofol requirements and the effect of hypothermic CPB is significantly more than that of normothermic CPB.