The state of intubated ICU patients: development of a two-dimensional sedation rating scale for critically ill adults

STUDY OBJECTIVES: To develop and evaluate an observer-rated instrument, the Minnesota Sedation Assessment Tool (MSAT), which is a measure of arousability, spontaneous muscle activity, and global sedation quality of mechanically ventilated adults. DESIGN: Paired raters assessment for reliability testing and observational design for validation testing. SETTING: Medical and surgical ICUs at a university-based hospital. PARTICIPANTS: Ninety-four intubated patients in ICUs and 93 ICU staff nurses. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The MSAT had very good overall reliability between raters, with the arousal scale (kappa = 0.85) having slightly better agreement than the motor activity scale (kappa = 0.72). The instrument had good coverage, very few missing values, and very good correlation with visual analog scales. The MSAT arousal scale had moderate correlation (rho = 0.68) with the analogous scale of a previously validated sedation instrument, the Vancouver Interaction and Calmness Scale. The correlation was weaker (rho = -0.41) between the MSAT motor activity scale and the calmness subscale, probably because of their dissimilar constructs. Both MSAT scales demonstrated convergent validity, whereas predictive validity was demonstrated in both a hypothetical scenario and in actual clinical practice for the MSAT arousal scale only. A patient's spontaneous motor activity was not associated with future sedative administration, with the possible exception of a more-sedated patient subgroup. CONCLUSIONS: The MSAT combines the efficiency of a single-item response format while permitting the separate reliable measurement of distinct observable characteristics of intubated patients. The level of consciousness of intubated patients influences the future administration of sedative medications. Spontaneous motor activity is less important in determining subsequent sedative use but may be useful as a comparative measure of patients' kinesiologic state during critical illness.