title: Response surface model predictions of wake-up time during scoliosis surgery.
abstract: BACKGROUND
  With the use of previously published data, new sevoflurane-remifentanil interaction models of various degrees of sedation were created and adapted to desflurane-fentanyl by using minimal alveolar concentration and opioid equivalencies. These models were used to predict return of responsiveness in patients undergoing scoliosis surgery during a wake-up test. Our hypothesis was that one of the interaction models would accurately predict return of responsiveness during a wake-up test.
  
  
  METHODS
  Three new sevoflurane-remifentanil interaction models were constructed from previous observations in volunteers by using the Observer's Assessment of Alertness/Sedation (OAA/S) scores. These models included predictions of OAA/S<2 (unresponsive), OAA/S< 3, and OAA/S<4 (sedation). Twenty-three patients scheduled for scoliosis surgery received a fentanyl-desflurane anesthetic. With the use of published pharmacokinetic models, predictions of fentanyl and desflurane effect-site concentrations were recorded throughout surgery and converted to equivalent remifentanil and sevoflurane effect-site concentrations. Data were recorded every 10 seconds from the time when desflurane was turned off until 10 minutes after the patients responded by moving their hands and toes. Model predictions were compared with observations with graphical and temporal analyses.
  
  
  RESULTS
  The average difference between the time when a patient first responded and the time when the model predicted that there was a 50% probability that the patient would respond were -2.6 ± 3.6 minutes (mean ± SD) for the OAA/S<2 model, 2.8 ± 5.6 minutes for the OAA/S<3 model and 52.6 ± 32.3 minutes for the OAA/S<4 model.
  
  
  CONCLUSIONS
  The results confirmed our study hypothesis; a sevoflurane-remifentanil interaction model built from observations in volunteers and adapted to desflurane and fentanyl accurately predicted patient response during a wake-up test. These results were similar to our previous study comparing model predictions and patient observations after a sevoflurane-remifentanil/fentanyl anesthetic. The OAA/S <2 model most accurately predicted the time patients would respond by moving their fingers and toes. This model may help anesthesiologists better predict return of responsiveness during a wake-up test in patients undergoing spine surgery.
authors.affiliation: From the *Department of Anesthesiology, Taipei Veterans General Hospital and National Yang-Ming University, Taipei, Taiwan; †Department of Anesthesiology, The University of Utah School of Medicine; ‡Department of Bioengineering, The University of Utah, Salt Lake City, Utah; §Department of Physics, Harvard University, Cambridge; and ‖Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts; ¶Department of Biomedical Engineering, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, P. R. China.
authors.forename: Chien-Kun
authors.initials: CK
authors.lastname: Ting
authors.forename: Ken B
authors.initials: KB
authors.lastname: Johnson
authors.forename: Wei-Nung
authors.initials: WN
authors.lastname: Teng
authors.forename: Noah D
authors.initials: ND
authors.lastname: Synoid
authors.forename: Cris
authors.initials: C
authors.lastname: Lapierre
authors.forename: Lu
authors.initials: L
authors.lastname: Yu
authors.forename: Dwayne R
authors.initials: DR
authors.lastname: Westenskow
mesh_terms: D000293:Adolescent; D018686:Anesthetics, Intravenous / Q000008:administration & dosage*; D002648:Child; D000077335:Desflurane; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage; D006801:Humans; D007530:Isoflurane / Q000031:analogs & derivatives; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage; D008954:Models, Biological; D010880:Piperidines / Q000008:administration & dosage; D011237:Predictive Value of Tests; D000077208:Remifentanil; D012600:Scoliosis / Q000188:drug therapy* / Q000601:surgery*; D000077149:Sevoflurane; D013997:Time Factors; D014851:Wakefulness / Q000187:drug effects* / Q000502:physiology; D055815:Young Adult
chemical_list: D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D010880:Piperidines; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane; D000077208:Remifentanil; D005283:Fentanyl