Objectives To compare levels of sedation in patients receiving continuous intravenous infusions of sedative/hypnotic or narcotic agents with levels in patients not receiving infusions and to compare subjective (Sedation-Agitation Scale) and objective (Bispectral Index) evaluations of sedation.

Methods Patients receiving mechanical ventilation in a medical intensive care unit were evaluated prospectively. Level of sedation was assessed with the Sedation-Agitation Scale (range 1–7, unarousable to dangerous agitation) and the Bispectral Index (range 0–100, flat line to awake waveform) recorded before and after stimulation. Patients were classified as receiving continuous infusions if an infusion had been administered within 24 hours preceding assessment.

Results Nineteen patients were evaluated on 80 occasions. Scores on the Sedation-Agitation Scale ranged from 1 to 5 (mean 2.6 and median 2) and correlated highly with values for the Bispectral Index (R2 = 0.48 before and 0.44 after stimulation, P < .001). Patients receiving continuous infusions were more deeply sedated than were patients receiving boluses or no medication (mean [SD] scores, Sedation-Agitation Scale: 2.1 [1.2] vs 3.3 [1.0], P < .001; Bispectral Index before stimulation: 63 [24] vs 86 [13], P < .001). Patients receiving continuous infusions were more likely to have a score of 2 or less on the Sedation-Agitation Scale (32/44 vs 8/35, P < .001).

Conclusion Objective and subjective assessments of sedation are highly correlated. Use of continuous infusions is associated with deeper levels of sedation, and patients receiving continuous infusions are more likely to be oversedated. Sedation therapy should be guided by subjective or objective assessment.

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