Assessing sedation during intensive care unit mechanical ventilation with the Bispectral Index and the Sedation-Agitation Scale

Objective: To describe the level of sedation for a cohort of mechanically v entilated adult intensive care unit (ICU) patients using validated subjecti ve and objective tools. Design: Prospective convenience sample. Setting.. Multidisciplinary 34-bed ICU at Maine Medical Center, a 599-bed n onuniversity, academic medical center. Patients.. Sixty-three adult ICU patients were monitored during 64 episodes of ventilatory support. Measurements and Main Results: Patients were prospectively evaluated by one trained investigator using the revised Sedation-Agitation Scale (SAS) and were simultaneously monitored for 1 to 5 hrs using the Bispectral Index (BI S), a numeric scale from 0 to 100 derived from the electroencephalogram. BI S values were assigned to baseline, stimulated, and average conditions for each patient by a separate investigator blinded to SAS scores. Ventilator s ettings, medications, and the lung injury severity (LIS) score were also re corded. Sedation levels varied from very deep sedation (SAS score = 1, BIS score = 43) to mild agitation (SAS score = 5, BIS score = 100). Heavily sed ated patients (SAS score = 1-2, n = 20) had higher Fro, (0.52 vs. 0.42, p = .008), oxygenation index (9.4 vs. 5.4, p = .03), and LIS scores (1.3 vs. 0 .7, p = .004) and lower baseline (66 vs. 78, p = .01), average (66 vs. 81, p < .001), and stimulated (89 vs. 96, p = .016) BIS scores compared with mo re awake patients. Patients with intermittent neuromuscular blockade use (n = 4) had higher Flo(2) (0.65 vs. 0.44, p = .006), minute ventilation (14.6 vs. 9.9 L/min, p = .005), positive end-expiratory pressure (7.5 vs. 4.8 cm H2O, p = .05), oxygenation index (15.7 vs. 6.0, p < .001), and LIS scores (3.3 vs. 1.0, p = .036) and were more sedated, with higher suppression rati os (3.5 vs. 0.6, p = .05) and lower SAS scores (1.5 vs. 4, p = .035). The a verage BIS values correlated well with SAS (r(2) = .21, p < .001). Conclusions: SAS and BIS work well to describe the depth of sedation for ve ntilated ICU patients. Deeper sedation and intermittent neuromuscular block ade were used for patients with greater ventilatory requirements and more s evere lung disease. The correlation between subjective and objective scales varied in medical, surgical, and trauma patients. Further research with SA S and BIS may facilitate the development of quantitative sedation guideline s for the led.