• Martin R Braathen, Ivan Rimstad, Terje Dybvik, Ståle Nygård, and Johan Raeder.
• Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
• Acta Anaesthesiol Scand. 2022 May 1; 66 (5): 598-605.

BackgroundIon mobility spectrometry (IMS) allows for online quantification of exhaled propofol concentrations. We aimed to validate a bedside online IMS device, the Edmon® , for predicting plasma concentrations of propofol in normal-weight and obese patients.MethodsPatients with body mass index (BMI) >20 kg/m2 scheduled for laparoscopic cholecystectomy or bariatric surgery were recruited. Exhaled propofol concentrations (CA ), arterial plasma propofol concentrations (CP ) and bispectral index (BIS) values were collected during target-controlled infusion (TCI) anaesthesia. Generalised estimation equation (GEE) was applied to all samples and stable-phase samples at different delays for best fit between CP and CA . BMI was evaluated as covariate. BIS and exhaled propofol correlations were also assessed with GEE.ResultsA total of 29 patients (BMI 20.3-53.7) were included. A maximal R2 of 0.58 was found during stable concentrations with 5 min delay of CA to CP ; the intercept a = -0.69 (95% CI -1.7, 0.3) and slope b = 0.87 (95% CI 0.7, 1.1). BMI was found to be a non-significant covariate. The median absolute performance error predicting plasma propofol concentrations was 13.4%. At a CA of 5 ppb, the model predicts a CP of 3.6 μg/ml (95% CI ±1.4). There was a maximal negative correlation of R2  = 0.44 at 2-min delay from CA to BIS.ConclusionsOnline monitoring of exhaled propofol concentrations is clinically feasible in normal-weight and obese patients. With a 5-min delay, our model outperforms the Marsh plasma TCI model in a post hoc analysis. Modest correlation with plasma concentrations makes the clinical usefulness questionable.© 2022 The Authors. Acta Anaesthesiologica Scandinavica published by John Wiley & Sons Ltd on behalf of Acta Anaesthesiologica Scandinavica Foundation.

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