ASSESSMENT OF DEPTH OF MIDAZOLAM SEDATION USING OBJECTIVE PARAMETERS

Objective: To determine the relationship between the clinically evalua ted depth of midazolam-induced sedation and the cardiac beat-to-beat v ariability (RR variability) in ICU patients in the intensive care unit (ICU). Design: Prospective study. Setting: ICU of a university hospit al. Patients: 20 consecutive patients studied during weaning from mech anical ventilation and withdrawal of midazolam-induced sedation. Measu rements and results: After clinical evaluation of depth of sedation ac cording to the Ramsay sedation score, the RR variability over 512 RR i ntervals and predominant respiratory rate were measured. The power spe ctrum of RR variability was calculated by a fast Fourier transformatio n and the resulting total frequency band (0.016-0.35 Hz) was subdivide d into a very low, a low, and a high frequency band. Stepwise multiple regression analysis in the first 10 patients (group 1) showed a signi ficant relationship between depth of sedation and measures of RR varia bility combined with respiratory rate (r(2) = 0.59, F = 12.1; p < 0.00 1). The more effective sedation was, the more depressed were both RR v ariability and predominant respiratory rate. Mean heart rate, mean res piratory rate, median deviation of RR intervals from the mean, and the ratio between spectral power density in the high and the low frequenc y bands proved to be the most important predictors of the Ramsay score (+/- 1 level accuracy: 87%, p < 0.001). Using this regression equatio n, the Ramsay score was predicted in the remaining 10 patients (group 2) with a +/- 1 level of accuracy of 81% (p < 0.001). Conclusion. In I CU patients, a significant correlation is found between the depth of m idazolam-induced sedation as assessed by the Ramsay sedation score and RR variability, with a clinically sufficient prediction accuracy. RR variability can serve as an objective, continuously available, and non -invasive measurement to monitor midazolam-induced sedation in intubat ed and mechanically ventilated patients.