Author: Michael Vlessides
The use of intraoperative bispectral index (BIS) monitoring is effective in reducing time to extubation, time to spontaneous eye opening, PACU time and consumption of anesthetics, according to the results of a recent systemic review and meta-analysis.
Nevertheless, the research team behind the study was quick to add that while BIS monitoring decreased the incidence of definite cases of intraoperative awareness, this difference was not statistically significant.
“The bispectral index has been widely used to assess the depth of anesthesia with the aim of reducing intraoperative awareness,” said Thomas Cheriyan, MD, a resident at Augusta University Medical Center, in Georgia. “Nevertheless, a seminal study by Myles et al [Lancet2004;363(9423):1757-1763], which showed a significant decrease in intraoperative awareness in patients who underwent BIS monitoring, has not been replicated in subsequent studies. In addition, the utility of BIS in reducing the use of inhaled and intravenous anesthetics has produced conflicting results.
The researchers searched the literature for randomized controlled trials comparing the effectiveness of BIS with controls in reducing:
“We also examined the risk of bias in each study using the Jadad scoring system,” Dr. Cheriyan said. The Jadad scale is used to grade the methodological quality of clinical trials using a scale of 0 to 5, with higher numbers indicating better quality.
Twenty-six randomized controlled trials were included in the final analysis, comprising 32,307 patients, with 14,664 who underwent BIS monitoring and 17,643 who served as controls. Nineteen studies were deemed to be at low risk for bias, while seven were medium risk.
Positive Effects of BIS
As Dr. Cheriyan reported at the 2018 annual meeting of the American Society of Anesthesiologists (abstract A3017), 18 of 14,062 patients (0.128%) in the BIS group reported definite intraoperative awareness. By comparison, 42 of 16,705 (0.25%) in the control group reported experiencing this sometimes devastating event. These differences were not statistically significant (odds ratio [OR], 0.50; 95% CI, 0.19-1.27; P=0.06).
Similarly, the study found no protective effect of BIS on definite and possible intraoperative awareness when compared with controls (OR, 0.83; 95% CI, 0.39-1.78; P=0.64).
Nevertheless, BIS monitoring was found to reduce:
- time to spontaneous eye opening, by an average of 1.3 minutes (95% CI, –2.28 to 0.32; P=0.010);
- time to extubation, by an average of 1.97 minutes (95% CI, –2.81 to –1.11; P<0.00001); and
- PACU discharge time, by an average of 4.8 minutes (95% CI, –10.18 to 0.58; P<0.0001).
The analysis found no difference between groups with respect to time to eye opening to verbal commands (95% CI, –3.31 to 0.64; P=0.19).
With respect to consumption of inhalational anesthetics, patients who underwent BIS monitoring consumed significantly less sevoflurane (effect size, –0.41; 95% CI, –0.76 to –0.07; P=0.02), desflurane (effect size, –0.52; 95% CI, –1.24 to 0.19; P<0.00001), and propofol (effect size, –0.83; 95% CI, –1.71 to 0.04; P<0.0001) than their counterparts who did not have BIS monitoring.
As Dr. Cheriyan discussed, the analysis was not without its shortcomings. “Obviously the limitations of all meta-analyses translate to this one,” he said. “We also found significant heterogeneity between studies with respect to study populations, sample size and surgery type. Furthermore, there were also limitations with the individual studies.”
Despite these fairly common drawbacks, the researchers were confident in the strength of their findings. “In summary, there’s a decreased incidence of definite awareness in the BIS group, but this is not statistically significant,” Dr. Cheriyan said. “Bispectral index monitoring is efficacious in reducing time to extubation, time to spontaneous eye opening, and time to PACU discharge, but, again, by just a modest amount.
“The utilization of BIS also reduces consumption of anesthetics,” he said. “We could not quantify the amount of anesthetics because there was significant heterogeneity in reporting of these outcomes among the studies.”
Session co-moderator Mark Rice, MD, a professor and the executive vice chair of anesthesiology at Vanderbilt University Medical Center, in Nashville, Tenn., questioned the clinical applicability of the meta-analysis. “Two questions come to mind immediately,” Dr. Rice said. “How do these findings help us in our own daily practice? Is there something we should or should not be doing?”
“Although the BIS is quite commonly used, I find that attending anesthesiologists are sometimes ambivalent about its use,” Dr. Cheriyan replied. “However, these data show that even though the device doesn’t statistically reduce the rate’s intraoperative awareness, it might prevent that one devastating incident. And that makes it worth it to me.
“What’s more, there was a Cochrane Review in May of 2018 [Cochrane Database Syst Rev2018;5:CD011283], which concluded that the use of an EEG device such as the BIS monitor may reduce the risk of postoperative cognitive dysfunction in patients aged 60 years or over undergoing noncardiac surgical and non-neurosurgical procedures at three months,” Dr. Cheriyan added. “So, I see it as an added tool at our disposal to monitor patients and potentially improve outcomes.”