Propofol in Exhaled Air and Plasma During Paedfusor Target‐Controlled Infusion in Children

Background

Target‐controlled infusion (TCI) algorithms for propofol are widely employed, but inter‐individual variability in achieved plasma concentrations highlights the likely potential value of real‐time monitoring. This prospective observational study evaluated the Exhaled Drug Monitor (Edmon) for online estimation of exhaled propofol concentrations ( C _A ) as a proxy for plasma propofol concentrations ( C _P ) in children. We also explored the relationships between Paedfusor‐estimated concentrations ( C _E–P ) and C _P , and between C _P and Bispectral Index (BIS).

Methods

Children undergoing propofol‐based anaesthesia with the Paedfusor TCI model had continuous recordings of C _A (parts per billion [ppb]) and C _E–P , with BIS values available in a subset of patients, as electrode placement was sometimes incompatible with the surgical field. Four arterial blood samples were obtained to determine C _P . Linear mixed‐model analyses were employed to assess the relationships between variables.

Results

Twenty‐six children aged 3–10 years were included. During maintenance of anaesthesia at a TCI target concentration of 3.0 μg mL ⁻¹ , C _A lagged behind C _P by 4 min. At this delay, the slope (gain) for estimation of C _P from C _A was 0.36 μg mL ⁻¹  ppb ⁻¹ (95% confidence interval [CI] 0.08 to 0.64, p  = 0.015) and the intercept (offset) 1.16 μg mL ⁻¹ (95% CI −0.52 to 2.84, p  = 0.16), RSquare 0.63. The pooled median absolute performance error based on samples obtained at 20 and 30 min after induction was 8.8% for the Edmon and 13.5% for the Paedfusor. C _P was 19%, 16% and 1% higher than Paedfusor predictions at 20 min, 30 min and end of surgery, respectively. In an exploratory analysis, BIS values decreased by 4.8 for each 1 μg mL ⁻¹ increase in C _P .

Conclusion

This exploratory study demonstrates that online monitoring of exhaled propofol during surgery is feasible in children. The Edmon provided estimates of C _P comparable with those of the Paedfusor algorithm during maintenance of anaesthesia, but its use is limited by a complex setup and a 4‐min time lag relative to plasma concentrations.

Editorial Comment

In this study, propofol infusion in children using a target‐controlled infusion was performed, and propofol concentration in exhaled air was sampled intermittently and measured. This assessment demonstrated practical feasibility aspects of this sampling and measurement along with challenges for clinical application.

Trial Registration: ClinicalTrials.gov (NCT04150432): URL: https://clinicaltrials.gov/study/NCT04150432?term=NCT04150432&rank=1