• Y H Lee, G H Choi, K W Jung, B H Choi, J Y Bang, E K Lee, B M Choi, and G J Noh.
• Department of Anaesthesiology and Pain Medicine, Asan Medical Centre, University of Ulsan College of Medicine, Seoul, Korea.
• Br J Anaesth. 2017 Jun 1; 118 (6): 883-891.

Background: In our preliminary study, the modified Marsh (M-Marsh) model caused an inadvertent underdosing of propofol in underweight patients. However, the predictive performance of the M-Marsh and Schnider models incorporated in commercially available target-controlled infusion (TCI) pumps was not evaluated in underweight patients.Methods: Thirty underweight patients undergoing elective surgery were randomly allocated to receive propofol via TCI using the M-Marsh or Schnider models. The target effect-site concentrations (Ces) of propofol were, in order, 2.5, 3, 4, 5, 6 and 2 μg ml -1 . Arterial blood samples were obtained at least 7 min after achieving each pseudo-steady-state.ResultsA total of 172 plasma samples were used to determine the predictive performance of both models. The pooled median (95% confidence interval) biases and inaccuracies at a target Ce ≤ 3 μg ml -1 were -22.6 (-28.8 to -12.6) and 31.9 (24.8-36.8) for the M-Marsh model and 9.0 (1.7-16.4) and 28.5 (21.7-32.8) for the Schnider model, respectively. These values at Ce ≥ 4 μg ml -1 were -9.6 (-16.0 to -6.0) and 24.7 (21.1-27.9) for the M-Marsh model and 19.8 (12.9-25.7) and 36.2 (31.4-39.7) for the Schnider model, respectively.ConclusionsThe pooled biases and inaccuracies of both models were clinically acceptable. However, the M-Marsh and Schnider models consistently produced negatively and positively biased predictions, respectively, in underweight patients. In particular, the M-Marsh model showed greater inaccuracy at target Ce   ≤   3 μg ml -1 and the Schnider model showed greater inaccuracy at target Ce ≥ 4 μg ml -1 . Therefore, it is necessary to develop a new pharmacokinetic model for propofol in underweight patients.Clinical Trial RegistrationKCT0001502.© The Author 2017. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com

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