title: An evaluation of remifentanil propofol response surfaces for loss of responsiveness, loss of response to surrogates of painful stimuli and laryngoscopy in patients undergoing elective surgery.
abstract: BACKGROUND
  In this study, we explored how a set of remifentanil-propofol response surface interaction models developed from data collected in volunteers would predict responses to events in patients undergoing elective surgery. Our hypotheses were that these models would predict a patient population's loss and return of responsiveness and the presence or absence of a response to laryngoscopy and the response to pain after surgery.
  
  
  METHODS
  Twenty-one patients were enrolled. Anesthesia consisted of remifentanil and propofol infusions and fentanyl boluses. Loss and return of responsiveness, responses to laryngoscopy, and responses to postoperative pain were assessed in each patient. Model predictions were compared with observed responses.
  
  
  RESULTS
  The loss of responsiveness model predicted that patients would become unresponsive 2.4 +/- 2.6 min earlier than observed. At the time of laryngoscopy, the laryngoscopy model predicted an 89% probability of no response to laryngoscopy and 81% did not respond. During emergence, the loss of responsiveness model predicted return of responsiveness 0.6 +/- 5.1 min before responsiveness was observed. The mean probability of no response to pressure algometry was 23% +/- 35% when patients required fentanyl for pain control.
  
  
  CONCLUSIONS
  This preliminary assessment of a series of remifentanil-propofol interaction models demonstrated that these models predicted responses to selected pertinent events during elective surgery. However, significant model error was evident during rapid changes in predicted effect-site propofol-remifentanil concentration pairs.
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, UT, USA. ken.b.johnson@hsc.utah.edu
authors.forename: Ken B
authors.initials: KB
authors.lastname: Johnson
authors.forename: Noah D
authors.initials: ND
authors.lastname: Syroid
authors.forename: Dhanesh K
authors.initials: DK
authors.lastname: Gupta
authors.forename: Sandeep C
authors.initials: SC
authors.lastname: Manyam
authors.forename: Talmage D
authors.initials: TD
authors.lastname: Egan
authors.forename: Jeremy
authors.initials: J
authors.lastname: Huntington
authors.forename: Julia L
authors.initials: JL
authors.lastname: White
authors.forename: Diane
authors.initials: D
authors.lastname: Tyler
authors.forename: Dwayne R
authors.initials: DR
authors.lastname: Westenskow
mesh_terms: D000328:Adult; D017558:Elective Surgical Procedures; D005260:Female; D006801:Humans; D007828:Laryngoscopy / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010147:Pain Measurement / Q000379:methods; D010149:Postoperative Pain / Q000378:metabolism / Q000517:prevention & control*; D010880:Piperidines / Q000493:pharmacokinetics / Q000627:therapeutic use*; D015742:Propofol / Q000493:pharmacokinetics / Q000627:therapeutic use*; D000077208:Remifentanil
chemical_list: D010880:Piperidines; D000077208:Remifentanil; D015742:Propofol