A secondary analysis of two large clinical trials fails to settle the question of whether use of the bispectral index (BIS) rather than end-tidal anesthetic concentration (ETAC) to monitor general anesthesia results in faster patient recovery.
The study, which appears in Anesthesiology, used data from the B-Unaware and BAG-RECALL trials, and therefore involved only patients considered to be at high risk for intraoperative awareness. However, the findings are in line with those of the recent Michigan Awareness Control Study, which was not restricted to high-risk patients.
On the other hand, both these studies contradict the most recent Cochrane review, which concluded that BIS monitoring resulted in more rapid postanesthesia care unit (PACU) recovery.
The current analysis includes 5884 patients from the B-Unaware and BAG-RECALL trials for whom the relevant data were available. The patients were randomly assigned to receive BIS- or ETAC-based monitoring and the primary endpoint was intraoperative awareness.
PACU recovery was a secondary endpoint, about which the anesthesiologists were not informed. However, lead researcher Michael Avidan (Washington University School of Medicine, St Louis, Missouri, USA) and team say that this could reduce the potential for bias.
The type of monitoring did not influence the time between application of dressings to the surgical site and the patient attaining an Aldrete score of at least 9, indicating good recovery from anesthesia. It also had no effect on the time to readiness for PACU discharge, which was dependent on Aldrete score, as well as on the absence of nausea and vomiting and uncontrolled pain.
Patients' risk for postoperative complications - specifically nausea and vomiting and severe pain - was unaffected by the type of monitoring they received, and the two groups had similar lengths of stay in the intensive care unit.
"This study does not provide evidence to support the hypothesis that maintaining higher intraoperative median BIS values leads to more rapid postoperative recovery or improved quality of recovery," say Avidan et al.
They outline several factors that could contribute to the discrepancy with other studies, including that the B-Unaware and BAG-RECALL trials used a strict protocol for the ETAC group. This could remove bias created by just one group receiving active, protocol-based monitoring as would happen when comparing BIS monitoring with routine clinical practice, say the researchers.
But they note that their findings "do not exclude the possibility that intraoperative BIS monitoring may be beneficial with respect to other outcomes."
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