Wintermeeting 2024: Johan Raeder

Measuring online exhaled propofol:
- feasible, useful, the future of TIVA, or a toy from the industry?

Johan Raeder^1,2
Saturday  9:30- 10:00

Co-Authors: Martin Rygh Braathen^1,2,  Ivan Rimstad², Terje Dybvik² Ståle Nygård³

¹ Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway

²Dept. of Anaesthesiology, Division of Critical Care, Oslo University Hospital, Oslo, Norway

³ Dept. of Informatics, Faculty of Mathematics and Natural Sciences, University of Oslo. Oslo Centre for Biostatistics and Epidemiology, University of Oslo, Oslo, Norway

Background/Introduction:
Ion Mobility Spectrometry (IMS) allows for online quantification of exhaled propofol concentrations. The concentrations are extremely low (parts per billion!) and the technology has so far been very cumbersome and only used for research purposes. Recently a commercial bedside online IMS device, the Edmon®, were developed for predicting plasma concentrations of propofol in everyday OR practice.

We got the opportunity to test this device in a series of gastrosurgical patients (normal weigt and obese) and children, by comparing exhaled propofol with plasma concentrations, TCI calculations and BIS measurements.

Methods:

1. Patients of 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 anaesthesia (Marsh, plasma target). 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 were also assessed with GEE.
2. Similar setup in a series of 26 children, age 3-10 years, with Paedfusor propofol guided infison.

Results:

1. 29 patients (BMI 20.3–53.7) were included. A maximal Rsquare of 0.6 was found during stable concentrations and with five minutes lag-time 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%. There was a maximal negative correlation of R=-0.44 at two minutes delay from BIS to CA.
2. Measurements were non-reliable during the first 20-30 min of infusion. Thereafter there was a correlation with Rsquare of 0,77 with 5 min delay. The limits of agreements were between -1.4 to 1.1 ng/ml.

Conclusions:
Online monitoring of exhaled propofol concentrations is clinically feasible, but very demanding. During induction there is no meaningful correlation with plasma samples. Modest correlation with plasma concentrations is present during maintenance, at 20-30 min after induction. The best correlations were found with incorporating delays between plasma propofol and exhaled propofol of five min.