Bispectral index correlates well with Richmond agitation sedation scale in mechanically ventilated critically ill patients

Abstract

Purpose: The clinical sedation scores available for assessing sedation in the intensive care unit (ICU) have drawbacks and limit their usefulness in paralyzed and deeply sedated patients. An objective tool, the bispectral index (BIS), could prove beneficial in such circumstances. We evaluated the ability of BIS to assess the level of sedation and its correlation with the Richmond agitation sedation scale (RASS) in ICU.

Methods: Twenty-four, mechanically ventilated, critically ill patients of either sex, 15-65 years of age, were studied over a period of 24 h. They received a standard sedation regimen consisting of a bolus dose of propofol 0.5 mg/kg and fentanyl 1 microg/kg followed by infusions of propofol and fentanyl ranging from 1.5 to 5 mg/kg/h and 0.5 to 2.0 microg/kg/h, respectively. Hemodynamic parameters, temperature, end-tidal carbon dioxide, BIS and RASS values were recorded. The correlation of BIS and RASS was expressed as Kendall correlation coefficients (tau). A p value of <0.05 was considered statistically significant.

Results: A total of 414 readings was obtained. On comparing BIS values for all patients with the corresponding RASS values, there was a statistically highly significant correlation between the two. (tau = 0.56, p < 0.0001). For adequate sedation as judged by a RASS value of 0 to -3, the median BIS value was found to be 56 (range 42-89). A BIS value of 70 had a high sensitivity (85%) and specificity (80%) to differentiate adequate from inadequate sedation.

Conclusion: Our results illustrate that BIS correlates well with RASS when assessing the level of sedation in mechanically ventilated critically ill patients. BIS reliably differentiates inadequate from adequate sedation.