Correlation Between Observational Scales of Sedation and Comfort and Bispectral Index Scores

When palliative care patients enter the phase of unconsciousness preceding death, it is standard practice to initiate or continue a subcutaneous infusion of an opioid plus or minus a sedative. The doses are determined somewhat empirically and adjustments are based on clinical assessment and observational measures of sedation and comfort. Following reports that these observational measures could be misleading, this study assesses their validity by comparing them with an objective measure of sedation, the Bispectral Index Score (BIS).

The objective of this study was to determine the validity of the Richmond Agitation and Sedation Scale (RASS) and the Patient Comfort Score (PCS) in assessing sedation and comfort in unconscious patients.

Forty eligible and consenting patients were monitored from the onset of unconsciousness (unresponsiveness) until death. Measures of sedation (RASS) and comfort (PCS) were made by the attending nurse every four hours. Correlation coefficients examined the relationship between fourth hourly RASS and PCS and time-matched BISs.

A significant correlation was found between RASS and BIS and PCS and BIS. Sedation and comfort scores were concentrated at the lower end of the respective scales, whereas time-matched BISs were widely scattered with scores ranging from near full awareness to deep sedation.

Compared with BIS, both RASS and PCS appear to be relatively blunt instruments at the lower end of their respective scales. Due caution should be taken interpreting and making clinical decisions based solely on the RASS and PCS and, by extension, other observational measures of patient comfort and sedation.