Influence of rate of administration on the mechanism behind propofol induced loss of consciousness

Abstract

Abstract Background Propofol effect-site time course models included in TCI systems have been under discussion. We hypothesized that the rate of administration is a major contributor affecting the construction of a useful effect-site model: yielding different plasmatic concentrations, loss of consciousness may occur by different mechanisms more complex than the pharmacological effect-site. Methodology ASA I II patients were randomized in two groups: rapid induction (RI) received TCI of propofol effect-site (CeCALC) 5.4 μg/mL (modified Marsh model), and slow induction (SI) propofol infusion of 10 mg/kg/hour. A neurologist, blinded to induction method, performed neurological assessments using the FOUR score until the loss of consciousness (LOC). At LOC, the presence of brain stem reflexes, EEG index (PSI) and infusion time/mass of drug were registered. Fisher's exact test was used to describe differences between brain stem reflexes and respiration components of the FOUR score and CeCALC for 4 propofo models at LOC time. Results 16 patients divided in two groups were included. All patient in SI had brainstem reflexes free at LOC. In the RI, all patients had brain stem reflexes abolished and 1 patient had B and R of 4 points in the FOUR score (brain stem reflexes unaffected; P Conclusions Depending of the infusion rate, propofol CeCALC at LOC calculated by different Pk/Pd models could be the source of confuse data to be used to guide the state of general anesthesia.