In this episode, I’ll discuss whether the bispectral index (BIS) correlates well to commonly used sedation scales.
Bispectral index is commonly used by anesthesia providers as a tool to ensure adequate loss of consciousness in the operating room and lessen the chance of accidental awareness during anesthesia. The use of BIS in critically ill patients is not well established. While clinical sedation scales are relied upon in the ICU to evaluate depth of sedation, there are some instances when these scales fail and an objective measure would be useful if it could indicate adequate sedation.
The most common instance for using BIS in the ICU is for patients who are receiving continuous neuromuscular blockade, as all clinical sedation scales fail when applied to a patient who is paralyzed with a neuromuscular blocking agent.
In an effort to better define the role of BIS in critically ill patients, a group of authors recently published in Pharmacotherapy a systematic review and meta-analysis of the correlation between bispectral index (BIS) and clinical sedation scales.
The review analyzed 24 studies with over 1200 patients evaluating the strength of correlation between concurrent assessments of BIS and Richmond Agitation Sedation Scale (RASS), Ramsay Sedation Scale (RSS), or Sedation Agitation Scale (SAS) in critically ill adult patients.
Importantly, the patients in these studies were not paralyzed because in order to use the BIS to evaluate sedation in a paralyzed patient, the correlation to the sedation scale must first be established in non-paralyzed patients.
The correlation between BIS and RASS, RSS, and SAS overall was 0.68 with the RASS coming in at 0.66, the RSS at 0.76, and the SAS at 0.53.
Although the RSS seemed to correlate better, this may be only because the RSS (like the big S) does not differentiate between varying levels of agitation but the RASS and SAS do.
The authors concluded
Based on the moderate correlation observed between BIS and clinical sedation scales in non-paralyzed patients, we hypothesize that BIS monitoring may provide meaningful information about level of consciousness that could improve sedation titration in patients receiving continuous NMBA…However, mapping specific BIS values to validated clinical sedation scales is hindered by heterogeneity across studies, and potential ceiling effects at the extremes of consciousness. This makes implementation of BIS at the bedside challenging. Although our findings represent an important step toward defining a role for BIS monitoring during paralysis, additional research is required to use BIS safely during NMBA treatment.
While future research is needed before widespread use of BIS in paralyzed patients can be recommended, pharmacists should familiarize themselves with the concept of using BIS to monitor sedation in the event that they encounter a unique patient scenario such as a difficult-to-sedate patient that also requires continuous paralysis.
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