Development of an index for assessment of nociception at incision during surgery

Abstract: Currently no objective direct indicator for nociception in anaesthetised patients exists. We aimed to find an indicator by combining physiological parameters obtained at the moment of skin incision during surgery. 55 females were anaesthetised with propofol-remifentanil target controlled infusions. Propofol was given to maintain a State Entropy of 50. Remifentanil target was randomised to 1, 3, or 5 ng/ml. Electrocardiogram, photoplethysmography (PPG), and EEG spectral entropy were recorded and analysed off-line, starting 60 s before and lasting until 120 s after skin incision. Patient reactions were annotated. Heart rate variability (HRV), PPG signal, and pulse transition time (PTT) related features were derived. Clinical signs, remifentanil levels and estimated intensity of incision were combined into a clinical score (CSSA) associated with probability of nociception. Physiological features were analysed to find a predictor (RN) of CSSA. This was achieved by combining features from HRV, spectral entropy, and PPG. The prediction-probabilty (Pk) of CSSA estimation was 0.74. RN was higher after larger incision (P=0.04), in movers (P=0.02), and in patients with lower remifentanil concentrations (P=0.00001). Concluding, RN seems to adequately monitor the components of analgesia: intensity of noxious stimulus and drug effect, and be related to clinical signs of inadequate analgesia