The objectives of this study were to: 1) study whether different linear and non-linear HRV measures may discriminate different levels of sedation in cardiac surgery patients; and 2) compare different linear and non-linear HRV measures in their performance and interrelationships

Heart rate variability (HRV) provides a noninvasive method to monitor functioning of the autonomous nervous system. HRV has been proposed as a potential tool for objective assessment of the level of sedation in critical care. In this paper we studied whether different linear and non-linear analysis methods may discriminate different levels of sedation in cardiac surgery patients. In addition we studied the interrelationships between the different parameters. The results show that HRV is modified by changes in the level of sedation, and that it is not completely recovered by the next day after the cardiac surgery. Both linear time and frequency domain parameters, and non-linear parameters discriminate the different levels, but especially the method based on Poincare plot analysis seems promising. As different parameters are closely correlated, a sub-set of parameters may be sufficient in the quantification of HRV in sedation.