Issues regarding propofol concentrations within the clinical range.

To the Editor: Recently, Gleason et al. have demonstrated that propofol at concentrations of 2 10 5 to 2 10 4 M relaxes guinea pig tracheal rings in organ baths in response to noradrenergic noncholinergic-mediated electrical field stimulation; these researchers have adopted the concentrations of propofol within this clinical range. The plasma concentration of propofol during the induction of anesthesia in humans has been reported as up to 3 10 5 M, and burst suppression doses of propofol for cerebral protection are up to 6 10 5 M. Effective concentrations of propofol (2 10 5 to 2 10 4 M) in the study by Gleason et al. are probably much higher than those with clinical relevance if considering plasma-free concentrations calculated from both above clinical plasma concentrations of propofol and the substantial binding of this compound to plasma proteins (97–98%). Therefore, it seems still unknown whether propofol actually protects against irritant-induced bronchoconstriction in those with the clinical condition. It would be helpful for clinicians to interpret their results if any future study is capable of showing the higher tissue uptake of propofol by the lung in their experimental condition.