We tested if microcomputer-based measurements of heart rate variabilit
y 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 af
ter physiotherapy, respectively (not significant). Ho we ver, the degr
ee of respiratory sinus arrhythmia, determined using circular statisti
cal 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 object
ive measurement of sedation in ICU patients and could form the basis o
f a simple sedation scoring system.