title: Effect-site concentration of remifentanil during patient-controlled analgesia in labour.
abstract: BACKGROUND
  Intravenous remifentanil has been described for patient-controlled analgesia in labour. Recently, the application of target-controlled infusion pumps with Minto's pharmacokinetic/pharmacodynamic model has been reported. Hypothetical effect-site remifentanil concentration during patient-controlled analgesia for labour has yet to be examined. The aim of this concept study was to explore characteristics of this parameter.
  
  
  METHODS
  We performed a historical cohort study based on our previous randomised cross-over clinical trial and analysed hypothetical effect-site remifentanil concentration. Values at spontaneous vaginal delivery and Apgar scores were tested for correlation. The association between pain score and the corresponding effect-site remifentanil concentration before and after bolus administration, and their relative difference, was examined with a linear mixed-effects model, adjusted for other variables.
  
  
  RESULTS
  A series of 23 parturients with uncomplicated singleton pregnancies were included. On average, effect-site remifentanil concentration was highest during the third quarter throughout our recordings (5.5ng/mL; maximum 15.8ng/mL). The mean (median) {IQR} [range] at spontaneous vaginal delivery (n=14) was 2.52 (1.32) {0.95-4.28} [0.65-6.88] ng/mL, all Apgar scores were >7, and no correlation was confirmed. A negative association between effect-site remifentanil concentration before bolus administration and pain score (scale 0-100) was observed (-3.9, 95% CI -5.16 to -2.61, P <0.01).
  
  
  CONCLUSIONS
  The residual value of hypothetical effect-site remifentanil concentration before uterine contraction, at the beginning of bolus administration, predicted lower pain scores. Monitoring effect-site remifentanil concentration may be potentially useful when remifentanil is administered for labour analgesia. However, our results need to be confirmed with a pharmacokinetic model optimized for pregnant patients.
authors.affiliation: Department of Anaesthesiology, Intensive Care and Pain Management, General Hospital Celje, Celje, Slovenia. Electronic address: tonijost@gmail.com.
authors.forename: A
authors.initials: A
authors.lastname: Jost
authors.affiliation: Institute for Biostatistics and Medical Informatics, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: R
authors.initials: R
authors.lastname: Blagus
authors.affiliation: Department of Anaesthesiology, Intensive Care and Pain Management, General Hospital Celje, Celje, Slovenia.
authors.forename: B
authors.initials: B
authors.lastname: Ban
authors.affiliation: Department of Anaesthesiology, Intensive Care and Pain Management, University Medical Centre Maribor, Maribor, Slovenia.
authors.forename: M
authors.initials: M
authors.lastname: Kamenik
mesh_terms: D016362:Analgesia, Obstetrical / Q000379:methods*; D016058:Analgesia, Patient-Controlled / Q000379:methods*; D000701:Analgesics, Opioid / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D048949:Labor Pain; D008297:Male; D010880:Piperidines / Q000493:pharmacokinetics*; D011247:Pregnancy; D000077208:Remifentanil
chemical_list: D000701:Analgesics, Opioid; D010880:Piperidines; D000077208:Remifentanil
keywords: Effect-site concentration; Labour pain; Patient-controlled analgesia; Pharmacokinetic modelling; Remifentanil