Design of ECG-based anaesthesia monitor/pain monitor

Design of anaesthesia monitor/ pain monitor, using ECG signal only, is presented in this paper. During surgical operations, ECG is picked-up as a routine procedure; the same ECG is used here, hence it is almost noninvasive. Initially heart rate variability (HRV) spectrum is obtained from R-R intervals (RRIs) and the respiratory peak is identified. Following the contour of this peak, a bandpass filter is designed using frequency sampling technique. The entire RRIs is then passed through this filter. The output contains the information about the respiratory cycles only and RSA (respiratory sinus arrhythmia) is obtained from it. It is assumed that, level of consciousness is proportional to RSA. Relaxation in the muscle is taken as overall relaxation of the body and parasympathetic dominance, as a measure of it, is obtained from the ratio of power in the respiratory and baroreceptor peaks. It is seen that the same instrument may be used as pain-monitor because unbalancing in the autonomic system (ANS) is also created during pain. A total of three dozen patients were tested, two dozens with anaesthetic drugs and the rest with thermal probe creating erythema. The results, in both the cases, are close to the expectation of the anaesthetists.