PURPOSE: ICU patients requiring mechanical ventilation may experience anxiety and discomfort leading to detrimental physiological consequences. Presently, the clinical scores used to assess the depth of sedation are subjective and inadequate, especially when neuromuscular blockers are used. Electroencephalograph (EEG)-based monitors such as patient state index (PSI)(PSA 4000)and bispectral index (BIS)(version XP)have been shown to provide quantifiable measures of the depth of sedation. This study examined the correlation between the depth of sedation scores determined by PSI and BIS relative to modified Ramsay score (MRS); a commonly used clinical sedation score.
METHODS: Postoperative cardiac surgery patients requiring ≤ 6 hours of mechanical ventilation were enrolled in the study. All patients received sedation with propofol infusion titrated to maintain MRS of 4-5(1= anxious/agitated/restless; 2= cooperative/oriented/tranquil; 3= drowsy/responds to commands only; 4= brisk response to shaking/loud sound; 5= sluggish response to shaking/loud sound; 6= no response). In addition to MRS, PSI and BIS values were recorded hourly for 6h. The bedside nurse was blinded to the PSI and BIS values. Data were analyzed using Spearman correlation coefficient.
RESULTS: 50 patients aged 62±7 years were studied. PSI and BIS values were recorded at 270 time points. A scatter plot of BIS and PSI scores showed positive correlation. Analysis using Spearman correlation coefficient showed a strong positive correlation between BIS and PSI values (Rho=0.731, p<0.001). There was intermediate negative correlation between MRS and BIS scores (Rho= −0.559, p<0.001) as well as MRS and PSI score (Rho= −0.450, p<0.001).
CONCLUSION: Our study suggests that there is intermediate correlation between MRS and BIS. The correlation between MRS and PSI score is even weaker. We found a strong correlation between MRS and PSI scores suggesting that these monitors are comparable for monitoring depth of sedation.
CLINICAL IMPLICATIONS: BIS and PSI are comparable objective monitors of depth of sedation. Both do not correlate well with the MRS. An alternative clinical sedation score may be needed to determine the acceptable range of BIS and PSI for sedation in the ICU.
DISCLOSURE: Adebola Adesanya, None.