Influence of bispectral index monitoring on decision making during cardiac anesthesia

Abstract

Study Objective To assess bispectral index (BIS) monitoring on decision making during cardiac surgery with cardiopulmonary bypass (CPB) by measuring the number of preset standardized comments with and without knowing the BIS value and by classifying the interventions following the BIS data. Design Prospective, randomized study. Setting University Hospital. Patients One hundred twenty-one patients scheduled for elective cardiac surgery (89 coronary patients, 24 valve replacement patients, and 8 valve replacement and coronary surgery). Interventions Patients were divided into 3 groups. An observing anesthesiologist recorded on a special form (“parallel” anesthesia record) data from the devices of the workstation and the BIS monitor. Conditions in which BIS monitoring was subjectively considered that might have been useful in anesthetic decision making were recorded as “events.” In group A (36 patients), the responsible anesthesiologist had continuous access to BIS information. In group B (44 patients), intraoperative anesthetic management was “blinded” to BIS values, whereas in group C (41 patients), the anesthesiologist observing the BIS monitor was free to inform the attending anesthesiologist about the BIS score. The number of events was considered as negatively reflecting the quality of the clinical course of a patient. The reduction of events was considered as improvement in decision making. All patients received the same anesthetic regimen (propofol + remifentanil). Monitoring was equal in all cases. Mild hypothermic CPB was applied in 73 patients. Statistical analysis used 1-way analysis of variance, Student 2-tailed t test, and χ 2 analysis. Main Results Patient demographic data, underlying pathology, operation performed, hypothermia application, times of anesthesia, duration of operation, and CPB were similar in the 3 groups. In group B, the BIS value was considered by the observer as useful to know in 220 events (5.00 ± 1.58 per patient). In group C, the BIS value was considered by the observer as useful to know in 143 events (3.49 ± 1.31 per patient, P < 0.001) and, at the same time, the attending anesthesiologist was informed about BIS. In 112 (78.3%) cases, measures were taken. Titration of anesthetic drugs was done in 79 (70.5%) patients, whereas titration of vasoactive drugs was done in 9 (8.0%) patients, titration of both in 13 (11.6%) patients, and other diagnostic or corrective actions in 11 (9.8%) patients. Distributions of BIS values did not differ statistically (39.19 ± 10.32, 37.38 ± 10.21, and 38.29 ± 10.01 in group A, group B, and group C, respectively). “Zenith” and “nadir” BIS values after induction also did not differ statistically. Awakening and extubation times were similar in both groups. Conclusions Subjectivity, although reduced as much as possible, can play a confining role in the value of our results. The usefulness of BIS monitoring is shown by the fact that BIS data resulted in corrective measures. Attending anesthesiologist's actions, based on BIS information, reduced the events in group C.