• Martin Soehle, Christina F Wolf, Melanie J Priston, Georg Neuloh, Christian G Bien, Andreas Hoeft, and Richard K Ellerkmann.
• From the University of Bonn, Bonn (MS, AH, RKE), Department of Anaesthesiology and Intensive Care Medicine, Sana Clinic Berlin-Lichtenberg, Berlin, Germany (CFW), C3P Analysis, Pharmacy Department, Plymouth Hospitals NHS Trust, Plymouth, United Kingdom (MJP), Department of Neurosurgery, University of Aachen, Aachen (GN), Department of Epileptology, University of Bonn, Bonn (CGB), Epilepsy Centre Bethel, Mara Hospital, Bielefeld, Germany (CGB) *Drs. Martin Soehle and Christina F. Wolf contributed equally to the writing of this article.
• Eur J Anaesthesiol. 2015 Aug 1; 32 (8): 527-34.

BackgroundAnaesthesia for awake craniotomy aims for an unconscious patient at the beginning and end of surgery but a rapidly awakening and responsive patient during the awake period. Therefore, an accurate pharmacokinetic/pharmacodynamic (PK/PD) model for propofol is required to tailor depth of anaesthesia.ObjectiveTo compare the predictive performances of the Marsh and the Schnider PK/PD models during awake craniotomy.DesignA prospective observational study.SettingSingle university hospital from February 2009 to May 2010.PatientsTwelve patients undergoing elective awake craniotomy for resection of brain tumour or epileptogenic areas.InterventionArterial blood samples were drawn at intervals and the propofol plasma concentration was determined.Main Outcome MeasuresThe prediction error, bias [median prediction error (MDPE)] and inaccuracy [median absolute prediction error (MDAPE)] of the Marsh and the Schnider models were calculated. The secondary endpoint was the prediction probability PK, by which changes in the propofol effect-site concentration (as derived from simultaneous PK/PD modelling) predicted changes in anaesthetic depth (measured by the bispectral index).ResultsThe Marsh model was associated with a significantly (P = 0.05) higher inaccuracy (MDAPE 28.9 ± 12.0%) than the Schnider model (MDAPE 21.5 ± 7.7%) and tended to reach a higher bias (MDPE Marsh -11.7 ± 14.3%, MDPE Schnider -5.4 ± 20.7%, P = 0.09). MDAPE was outside of accepted limits in six (Marsh model) and two (Schnider model) of 12 patients. The prediction probability was comparable between the Marsh (PK 0.798 ± 0.056) and the Schnider model (PK 0.787 ± 0.055), but after adjusting the models to each individual patient, the Schnider model achieved significantly higher prediction probabilities (PK 0.807 ± 0.056, P = 0.05).ConclusionWhen using the 'asleep-awake-asleep' anaesthetic technique during awake craniotomy, we advocate using the PK/PD model proposed by Schnider. Due to considerable interindividual variation, additional monitoring of anaesthetic depth is recommended.Trial RegistrationClinicalTrials.gov identifier: NCT 01128465.

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