Respiratory sinus arrhythmia: a new, objective sedation score.

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.