Skin Conductance Fluctuations Correlate Poorly with Postoperative Self-report Pain Measures in School-aged Children

Background: The number of fluctuations of skin conductance per second (NFSC) has been shown to correlate with induced pain and self-report pain scales. This study aimed to evaluate the validity and feasibility of NFSC as an objective measurement of nociception intensity in school-aged children after surgery. Methods: After approval by the research ethics board and obtaining consent, 100 subjects participated in this prospective observational study. Preoperatively, NFSC was measured for 60 s at rest and during response to a self-report pain scale (numeric rating scale [NRS], Faces Pain Scale-Revised) and anxiety scoring (NRS). Postoperative measurements were repeated every 10 min for 30 min or until NRS pain score was <= 4 for two consecutive scores. Spearman rank correlation coefficients were calculated to investigate the relationship between NFSC and NRS pain, Faces Pain Scale-Revised, and NRS anxiety. The clinical utility of using NFSC in determining NRS pain threshold was investigated using receiver operator characteristics analysis. For clinical relevance, a cutoff NFSC was chosen that optimizes both specificity and sensitivity. Although selecting a low cutoff value increases the sensitivity of the NFSC in diagnosing pain, it does so at the expense of specificity. Results: Data from 90 subjects (64.4% male) aged 7-17 yr (median age 13 yr) were analyzed (217 postoperative datasets). NFSC correlated weakly with NRS pain scores (P = 0.21; P < 0.002). NFSC did not correlate with NRS anxiety scores (P = 0.15, P < 0.03). NRS pain scores correlated strongly with Faces Pain Scale-Revised (P = 0.89, P < 0.0001) and weakly with NRS anxiety scores (P = 0.34, P < 0.0001). A threshold of 0.23 NFSC predicted severe pain (NRS >= 7) with 56.3% sensitivity (95% CI = 37.7-73.6%) and 78.4% specificity (95% CI = 71.7-84.1%). The area under receiver operator characteristic curve for NFSC was 69.1%. Conclusions: NFSC measurement is feasible in a perioperative setting but was not specific for postoperative pain intensity and was unable to identify analgesia requirements when compared with self-report measures.