title: Objective assessment of the immediate postoperative analgesia using pupillary reflex measurement: a prospective and observational study.
abstract: BACKGROUND
  The evaluation of pain intensity during the immediate postoperative period is a key factor for pain management. However, this evaluation may be difficult in some circumstances. The pupillary dilatation reflex (PDR) has been successfully used to assess the analgesic component of a balanced anesthetic regimen. We hypothesized that PDR could be a reliable index of pain intensity and could guide morphine administration in the immediate postoperative period.
  
  
  METHODS
  One hundred patients scheduled to undergo general surgery were included in this prospective observational study. Pain intensity was assessed by using a simple five-item verbal rating scale (VRS). After patients awoke from general anesthesia, those experiencing mild or more severe pain (VRS more than 1) received intravenous morphine titration. Before and after intravenous morphine titration, the PDR induced by a standardized noxious stimulus was measured with a portable pupillometer. A receiver-operating curve was built to estimate the accuracy of PDR in objectively detecting patients requiring morphine titration. Results are given as median (95% CI).
  
  
  RESULTS
  On the initial evaluation, a correlation was found between VRS and PDR (ρ = 0.88 [0.83-0.92], P < 0.0001). In the 39 patients that had a VRS more than 1, PDR before and after morphine titration was respectively 35% (31-43) versus 12% (10-14); P < 0.0001. The PDR threshold value corresponding to the highest accuracy to have VRS more than 1 was 23%, with 91% and 94% sensitivity and specificity, respectively.
  
  
  CONCLUSIONS
  In the immediate postoperative period, the PDR is significantly correlated with the VRS. The pupillometer could be a valuable tool to guide morphine administration in the immediate postoperative period.
authors.affiliation: Department of Anesthesia and Intensive Care, Assistance Publique, Hôpitaux de Paris, St. Antoine University Hospital, Paris, France.
authors.forename: Mourad
authors.initials: M
authors.lastname: Aissou
authors.forename: Aurelie
authors.initials: A
authors.lastname: Snauwaert
authors.forename: Claire
authors.initials: C
authors.lastname: Dupuis
authors.forename: Arthur
authors.initials: A
authors.lastname: Atchabahian
authors.forename: Frederic
authors.initials: F
authors.lastname: Aubrun
authors.forename: Marc
authors.initials: M
authors.lastname: Beaussier
mesh_terms: D016058:Analgesia, Patient-Controlled; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000627:therapeutic use; D000758:Anesthesia; D016477:Artifacts; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage / Q000627:therapeutic use; D010147:Pain Measurement / Q000379:methods*; D010149:Postoperative Pain / Q000175:diagnosis* / Q000188:drug therapy*; D011187:Posture; D011446:Prospective Studies; D012372:ROC Curve; D012025:Reflex, Pupillary / Q000187:drug effects*; D015203:Reproducibility of Results
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine