• X Wang, X Chen, S Ye, Y Feng, C Huang, L Hou, J Liu, and H Chen.
• The Key Laboratory of Biomedical Engineering of Ministry of Education, College of Biomedical Engineering and Instrument Science, Zhejiang University, Zhejiang, China.
• Anaesthesia. 2012 Dec 1; 67 (12): 1332-6.

AbstractAutonomic sympathetic activation, for instance following noxious stimuli, decreases the size and flattens the shape of the photoplethysmographic peripheral pulse waveform. We report a simple measure of the waveform shape, the ratio of mean-to-peak wave amplitude, for measuring nociception level during general anaesthesia. Fifty participants, anaesthetised with propofol and remifentanil, were randomly allocated to one of three different remifentanil effect-site concentrations (1, 3 and 5 ng.ml(-1) ). Tracheal intubation increased the mean (SD) plethysmographic ratio from 0.38 (0.06) to 0.48 (0.04), p = 2.6 × 10(-16) . The mean (SD) ratios following intubation at remifentanil effect-site concentrations of 1 ng.ml(-1) , 3 ng.ml(-1) and 5 ng.ml(-1) , were 0.49 (0.03), 0.48 (0.03) and 0.45 (0.04), respectively. Remifentanil therefore suppressed changes in the mean-to-peak ratio caused by tracheal intubation (p = 0.006). The ratio of the mean-to-peak plethysmographic amplitude may represent a simple measure of the balance of autonomic sympathetic and parasympathetic activity under general anaesthesia, and its performance following intubation was significantly different from peak amplitude (p = 0.046).Anaesthesia © 2012 The Association of Anaesthetists of Great Britain and Ireland.

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