Adhesion of volatile propofol to breathing circuit tubing

Abstract

Propofol in exhaled breath can be measured and may provide a real-time estimate of plasma concentration. However, propofol is absorbed in plastic tubing, thus estimates may fail to reflect lung/blood concentration if expired gas is not extracted directly from the endotracheal tube. We evaluated exhaled propofol in five ventilated ICU patients who were sedated with propofol. Exhaled propofol was measured once per minute using ion mobility spectrometry. Exhaled air was sampled directly from the endotracheal tube and at the ventilator end of the expiratory side of the anesthetic circuit. The circuit was disconnected from the patient and propofol was washed out with a separate clean ventilator. Propofol molecules, which discharged from the expiratory portion of the breathing circuit, were measured for up to 60 h. We also determined whether propofol passes through the plastic of breathing circuits. A total of 984 data pairs (presented as median values, with 95% confidence interval), consisting of both concentrations were collected. The concentration of propofol sampled near the patient was always substantially higher, at 10.4 [10.25-10.55] versus 5.73 [5.66-5.88] ppb (p < 0.001). The reduction in concentration over the breathing circuit tubing was 4.58 [4.48-4.68] ppb, 3.46 [3.21-3.73] in the first hour, 4.05 [3.77-4.34] in the second hour, and 4.01 [3.36-4.40] in the third hour. Out-gassing propofol from the breathing circuit remained at 2.8 ppb after 60 h of washing out. Diffusion through the plastic was not observed. Volatile propofol binds or adsorbs to the plastic of a breathing circuit with saturation kinetics. The bond is reversible so propofol can be washed out from the plastic. Our data confirm earlier findings that accurate measurements of volatile propofol require exhaled air to be sampled as close as possible to the patient.

Quantification of exhaled propofol is not feasible during single‐lung ventilation using double‐lumen tubes: A multicenter prospective observational trial

“…Moreover, propofol concentration sampled directly from the endotracheal tube was substantially higher than at the expiratory end of the breathing circuit. 11 Additionally, propofol absorption depends on the material itself: silicone, polyurethane and tygon absorb virtually the entirety of volatile propofol, while, in contrast, perfluoralkoxy and polytetrafluorethylene only absorb a negligible amount. 5 Therefore, the larger inner surface area using both lumens during double-lung ventilation possibly explains lower volatile propofol concentrations.…”

“…Lorenz et al demonstrated that propofol reversibly binds to plastic tubes and breathing circuits, exhibiting saturation kinetics. Moreover, propofol concentration sampled directly from the endotracheal tube was substantially higher than at the expiratory end of the breathing circuit 11 . Additionally, propofol absorption depends on the material itself: silicone, polyurethane and tygon absorb virtually the entirety of volatile propofol, while, in contrast, perfluoralkoxy and polytetrafluorethylene only absorb a negligible amount 5 .…”

Correlation of exhaled propofol with Narcotrend index and calculated propofol plasma levels in children undergoing surgery under total intravenous anesthesia - an observational study

“…Lorenz at al. demonstrated the behavior of propofol in breathing circuits in an ICU setting where propofol was outgassed from the breathing circuit for hours and remained at 2.8 ppb after 60 h of washing out [ 23 ]. In laboratory studies, perfluoroalkoxy alkanes (PFA) have been identified as materials with low adsorption of propofol [ 24 ].…”

Calibration and validation of ultraviolet time-of-flight mass spectrometry for online measurement of exhaled ciprofol

“…One reason for this effect may be the adhesion of ciprofol to the internal surfaces of the gas generator and the UV-TOFMS. [29][30][31] All of these surfaces have the potential to contribute to carry over. The interaction of gaseous ciprofol with plastic and stainless-steel surfaces should be further investigated.…”