We tested if microcomputer-based measurements of heart rate variability and respiratory sinus arrhythmia (RSA) could be used as the basis of an objective sedation score. Measurements were obtained in eight ICU patients before, during and after physiotherapy. Patients were sedated with propofol and alfentanil and paralysed with atracurium. Mean ECG R-R interval showed little variation, changing from 646.15 (SD 203.15) ms to 596.08 (181.75) ms and 633.98 (184.53) ms before, during and after physiotherapy, respectively (not significant). However, the degree of respiratory sinus arrhythmia, determined using circular statistical analysis, increased significantly, from 0.14 (0.11) to 0.24 (0.15), during physiotherapy and returned to control after physiotherapy (P < 0.05). Changes in respiratory sinus arrhythmia may provide an objective measurement of sedation in ICU patients and could form the basis of a simple sedation scoring system.

Auditory evoked response (AER) was recorded before, during and after physiotherapy in 11 paralysed (atracurium 0.56 (SD) 0.13 mg kg-1 h-1), sedated (propofol 2.2 (1.0) mg kg-1 h-1; fentanyl 4.4 (2.3) micrograms kg-1 h-1) and critically ill patients undergoing ventilation in the intensive care unit (ICU). The latency of the negative wave, NB, was reduced by physiotherapy (mean 44.8 (SD) 7.9 ms before, 41.0 (6.8) ms during (P less than 0.01, non-parametric Friedman test) and 45.6 (6.3) ms after physiotherapy); NB amplitude showed no consistent change (-0.81 (1.4) microV, -0.81 (1.5) microV and -0.71 (1.3) microV, respectively). NB latency responded to patient arousal at constant levels of sedation and this requires further evaluation as a means of monitoring sedation in paralysed patients in the ICU.