Background: A means of identifying the presence and severity of pain that is not reliant on the subjective assessment of pain is desirable whenever a patient self-rating of pain cannot be easily obtained (e.g. sedated patients, very young children, individuals with learning difficulties). The heart rate variability based analgesia nociception index (ANI) has been proposed to reflect different levels of acute pain. The aim of this study was to compare ANI scores with a numeric rating scale (NRS, 0-10) based on self-assessment of pain in the recovery room.
Methods: One hundred and twenty patients after non-emergency surgery were included. On arrival in the post-anaesthesia care unit (PACU) and subsequently at 5 min intervals, patients were asked to rate their level of pain on a 0-10 NRS. ANI values 0-100 points (low values indicating higher levels of pain) were recorded simultaneously.
Results: Eight hundred and sixteen pain ratings from 114 patients were included in the analysis. A small but statistically significant negative correlation was found between ANI and the NRS scores (ρ=-0.075; P=0.034). A small but significant difference in ANI was found comparing the extremes of pain [mean (se): NRS 0: 63 (1.4) vs NRS 6-10: 59 (1.4); P=0.027]. However, a receiver-operating analysis testing the value of ANI to distinguish between NRS 0 and NRS 6-10 revealed only low sensitivity and specificity.
Conclusion: ANI did not reflect different states of acute postoperative pain measured on a NRS scale after adult sevoflurane-based general anaesthesia.
Keywords: analgesia, postoperative; pain, postoperative.