title: Surgical pleth index: prediction of postoperative pain and influence of arousal.
abstract: BACKGROUND
  There are conflicting reports concerning the outcome after anaesthesia guided by the surgical pleth index (SPI; GE Healthcare, Helsinki, Finland). One potential explanation may be the lack of evidence for the selection of SPI cut-off values. The aim of this trial was to investigate the correlation between SPI, arousal, and postoperative pain and to define a cut-off value for SPI to predict moderate-to-severe pain.
  
  
  METHODS
  After obtaining ethical approval and written informed consent, 70 patients undergoing non-emergency surgery were enrolled. Data relating to SPI, heart rate, mean arterial pressure, and state entropy were recorded every 10 s for the last 10 min of surgery (state entropy <60 at all times). Subsequently, recordings continued during the phase of arousal. After recovery room admission, pain scores (numerical rating scale 0-10) were obtained every 3 min for 15 min.
  
  
  RESULTS
  Data from 65 patients were analysed. Receiver-operating characteristic curve analysis revealed an optimal intraoperative cut-off SPI value of 30 to discriminate between numerical rating scale scores 0-3 and 4-10. For this value, the negative and positive predictive values to discriminate between numerical rating scale scores 0-3 and 4-10 were 50 and 89.7%, respectively. The SPI was significantly affected by arousal, and SPI scores obtained during this phase were not predictive of postoperative pain.
  
  
  CONCLUSIONS
  Surgical pleth index values are predictive of postoperative pain only if obtained before patient arousal. In contrast to previous studies, a relatively low SPI, >30, appears to predict pain with a high positive predictive value and may therefore be suggested for future studies of SPI-guided anaesthesia.
  
  
  BACKGROUND
  Australian New Zealand Clinical Trials Registry: ACTRN12615000804583.
authors.affiliation: School of Medicine and Pharmacology, University of Western Australia, Level 2 Royal Perth Hospital MRF Building, Rear 50 Murray Street, Perth, WA 6000, Australia Department of Anaesthesia and Pain Medicine, Royal Perth Hospital, Perth, WA, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Ledowski
authors.affiliation: Faculty of Medicine, Christian-Albrechts-University Kiel, Kiel, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Burke
authors.affiliation: Department of Anaesthesia, Armadale Health Services, Perth, WA, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Hruby
mesh_terms: D000328:Adult; D001143:Arousal; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010149:Postoperative Pain / Q000175:diagnosis*; D010991:Plethysmography; D011237:Predictive Value of Tests
keywords: anaesthesia; monitoring intraoperative; nociception; postoperative pain; pulse wave analysis