Maintaining tight BIS range may improve long-term surgical outcomes
Avoiding prolonged low intra-operative bispectral index (BIS) values may improve patients’ long-term outcomes, shows an analysis of the B-Aware trial.
The primary B-Aware trial findings showed that intra-operative BIS monitoring reduced intra-operative awareness by up to 82% in high-risk patients.
To investigate whether the lower doses of hypnotic drugs achieved with BIS monitoring translates to a reduction in morbidity or mortality, Kate Leslie (Royal Melbourne Hospital, Australia) and team followed-up 1947 of the original 2463 patients, a median of 4.1 years after recruitment. In all, 22.2% of patients had died: 8.9% of myocardial infarction (MI) and 4.7% of stroke.
Overall, propensity score analysis showed that patients assigned to BIS monitoring were no more or less likely to die than those given routine care. Among patients randomly assigned to BIS monitoring, those with prolonged low values (less than 40 for more than 5 minutes) were no more likely to die than routine care patients.
But patients who avoided prolonged low BIS values were 34% more likely to survive than routine care patients, reports the team in the journal Anesthesia and Analgesia.
Patients who did have prolonged periods of low BIS values were 1.94-fold more likely to suffer MI and 3.32-fold more likely to suffer stroke than other BIS-monitored patients.
Avoiding a prolonged low BIS value reduced the risk for MI and stroke relative to routine care, particularly for patients undergoing emergency surgery.
In an accompanying editorial, Jiro Kurata (Kyoto University School of Medicine, Japan) noted that low BIS values are not just caused by anesthetic overdose.
Patients in the B-Aware trial were high risk for peri-operative morbidity; “therefore an incidence of BIS below 40 for more than 5 minutes might have resulted primarily from circulatory depression rather than an absolute anesthetic overdose,” he noted.
Kurata said: “The impact of deep hypnosis on the prognosis of surgical patients must await a future randomized controlled trial that controls for other predictive factors such as comorbidity, malignancy, age, intra-operative circulatory status, and viability of major organs.”
“Nonetheless, the information offered by the present retrospective survey motivates us toward a better anesthetic management using the strict titration of BIS to values between 40 and 60.”
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By Eleanor McDermid