Effects of Preservatives in Propofol. Brown et al. (page 851)
A new formulation of propofol with metabisulfite preservative has been introduced. Because metabisulfite has been shown to cause airway narrowing in asthmatic individuals, Brown et al. designed a study to test the effects of propofol with and without metabisulfite on bronchoconstriction in sheep. In seven animals, anesthesia was induced with intramuscular ketamine and maintained with pentobarbital, and then the animals underwent mechanical ventilation. After a 30-min recovery period, baseline airways resistance (Raw) was measured. Then, Rawwas measured during vagal nerve stimulation, at recovery after 2 or 3 min, and after a methacholine challenge. Allowing another 3–5 min for recovery to baseline Rawlevels, the investigators administered propofol with and without metabisulfite, lidocaine (5 mg/ml), or metabisulfite alone (0.125 mg/ml) into the bronchial artery, in random order, at a rate of 0.06, 0.2, and 0.6 ml/min. Allowing 10 min after each infusion, the authors then repeated Rawmeasurements before and after vagal nerve stimulation and methacholine challenges. The Rawat baseline (before challenges) was not significantly different among the four drugs. Both lidocaine and propofol without metabisulfite caused a dose-dependent attenuation of vagal nerve stimulation–induced bronchoconstriction. Propofol with metabisulfite had no effect on vagal nerve stimulation–induced bronchoconstriction or on response to the infusion of methacholine. Because of the similarity of the airway response to the vagal nerve stimulation– and methacholine- induced bronchoconstriction during metabisulfite infusion, the authors’ results suggest that metabisulfite affects both neural and direct airway smooth muscle–induced bronchoconstriction. This preservative used in propofol can have an effect on the ability of propofol to attenuate bronchoconstriction.