Pain/analgesia evaluation using heart rate variability analysis.

The optimization of analgesic drugs delivery during general anesthesia requires to evaluate the pain/analgesia balance. Heart rate variability analysis has been shown in several studies to measure the autonomic nervous system tone, which is strongly influenced by anesthetic drugs. Recording RR series during general anesthesia enabled us to observe that the respiratory sinus arrhythmia pattern changed when a surgical stimulation was painful, even though the patient was not conscious. We developed a pain/analgesia evaluation algorithm based on the magnitude analysis of the respiratory patterns on the RR series. The parameters computed from this algorithm were recorded in thirty nine patients during general anesthesia. We retrospectively compared our parameters at different levels of analgesia during surgical stimulation, and found that they were related to pain/analgesia and relatively independent from other anesthesia related events like hypnosis and haemodynamic conditions.