Online exhaled propofol monitoring in normal-weight and obese surgical patients.

Abstract

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 R 2 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 R 2 = 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.