• Christine H Meyer-Frießem, Gunnar Jess, Esther M Pogatzki-Zahn, and Peter K Zahn.
• Department of Anaesthesiology, Intensive Care Medicine, Palliative Care and Pain Management, BG-Universitätsklinikum Bergmannsheil GmbH Bochum, Medical Faculty of Ruhr University Bochum, Bürkle-de-la-Camp-Platz 1, 44789 Bochum, Germany. Electronic address: meyer-friessem@ains-bergmannsheil.de.
• Scand J Pain. 2017 Jul 1; 16: 129-135.

BackgroundPain assessment by Numeric Rating Scale (NRS) is considered to be good clinical practice, but objective pain assessment is still a challenge. Near infrared spectroscopy (NIRS) measures cerebral tissue oxygen saturation (SctO2) that increases with cortical-neuronal activity and may provide point-of-care bedside pain monitoring. Analogous to promising studies in newborns, we hypothesize that different levels of SctO2 can probably quantify pain intensity. SctO2 may increase following painful in contrast to non-painful or sham stimuli and may correlate with pain intensity as assessed by NRS in volunteers.MethodsTwenty healthy male students (24.2±1.9 years), recruited via local advertising, were consecutively included in a sequence-randomized, sham-controlled, single-blinded study. SctO2 was recorded continuously with two NIRS sensors on the forehead. After resting, four stimuli were applied in a random order on the right forearm (unexpected and expected electrical pain, expected non-painful and sham stimuli). Blinded subjects were asked to rate each stimulus on NRS.StatisticsRM-ANOVA; Wilcoxon or paired Student t-test; Spearman's rank correlation; P<.05.ResultsResting volunteers showed SctO2 of 72.65%±3.39. SctO2 significantly increased for about 60 to 70s until a maximum after unexpected painful (74.62%±3.9; P=.022) and sham stimuli (74.07%±3.23; P=.014). Expected painful (P=.139) and non-painful stimuli (P=.455) resulted in no changes in SctO2. NRS scores (median, IQR) were rated significantly higher after expected (5.25, 3.5 to 6.75) than after unexpected (4.5, 3 to 5; P=.008) pain. No strong correlation was found between NRS and SctO2.Conclusions And ImplicationsContrary to our expectations, measuring SctO2 via a two-channel NIRS is not able to remediate the lack of objective bedside pain assessment under standardized experimental conditions in alert adults.Trial RegistrationDRKS 00011575 (retrospectively registered).Copyright © 2017 Scandinavian Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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