title: Responses of heart rate variability to acute pain after minor spinal surgery: optimal thresholds and correlation with the numeric rating scale.
abstract: BACKGROUND
  The autonomic nervous system is influenced by many stimuli including pain. Heart rate variability (HRV) is an indirect marker of the autonomic nervous system. Because of paucity of data, this study sought to determine the optimal thresholds of HRV above which the patients are in pain after minor spinal surgery (MSS). Secondly, we evaluated the correlation between HRV and the numeric rating scale (NRS).
  
  
  METHODS
  Following institutional review board approval, patients who underwent MSS were assessed in the postanesthesia care unit after extubation. A laptop containing the HRV software was connected to the ECG monitor. The low-frequency band (LF: 0.04 to 0.5 Hz) denoted both sympathetic and parasympathetic activities, whereas the high-frequency band (HF: 0.15 to 0.4 Hz) represented parasympathetic activity. LF/HF was the sympathovagal balance. Pain was quantified by the NRS ranging from 0 (no pain) to 10 (worst imaginable pain). Simultaneously, HRV parameters were noted. Optimal thresholds were calculated using receiver operating characteristic curves with NRS>3 as cutoff. The correlation between HRV and NRS was assessed using the Spearman rank test.
  
  
  RESULTS
  We included 120 patients (64 men and 56 women), mean age 51±14 years. The optimal pain threshold values were 298 ms for LF and 3.12 for LF/HF, with no significant change in HF. NRS was correlated with LF (r=0.29, P<0.005) and LF/HF (r=0.31, P<0.001) but not with HF (r=0.09, NS).
  
  
  CONCLUSIONS
  This study suggests that, after MSS, values of LF>298 m and LF/HF>3.1 denote acute pain (NRS>3). These HRV parameters are significantly correlated with NRS.
authors.affiliation: Departments of *Anesthesiology and Intensive Care ‡Neurosurgery, Pellegrin University Hospital, Bordeaux †Department of Neurosurgery, Toulouse University Hospital, Toulouse, France.
authors.forename: Musa
authors.initials: M
authors.lastname: Sesay
authors.forename: Georges
authors.initials: G
authors.lastname: Robin
authors.forename: Patrick
authors.initials: P
authors.lastname: Tauzin-Fin
authors.forename: Oumar
authors.initials: O
authors.lastname: Sacko
authors.forename: Edouard
authors.initials: E
authors.lastname: Gimbert
authors.forename: Jean-Rodolphe
authors.initials: JR
authors.lastname: Vignes
authors.forename: Dominique
authors.initials: D
authors.lastname: Liguoro
authors.forename: Karine
authors.initials: K
authors.lastname: Nouette-Gaulain
mesh_terms: D059787:Acute Pain / Q000188:drug therapy / Q000503:physiopathology*; D000328:Adult; D000762:Anesthesia Recovery Period; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods*; D017288:Pain Threshold; D010149:Postoperative Pain / Q000188:drug therapy / Q000503:physiopathology*; D011446:Prospective Studies; D012372:ROC Curve; D013131:Spine / Q000601:surgery*; D013564:Sympathetic Nervous System / Q000503:physiopathology; D055815:Young Adult