We know that lidocaine is a local anesthetic. In some animal and human studies, it has been shown to reduce general anesthetic properties. Can lidocaine decrease the minimum alveolar concentration of anesthetic that prevents movement in 50% of subjects in response to a noxious stimulus (MAC) of sevoflurane? In order to determine the answer to this question, Dr. Thomas Hamp, Medical University Vienna, Vienna, Austria, and colleagues administered 1.5 mg•kg-1 intravenous lidocaine to adults undergoing general anesthesia for a procedure that required a skin incision of at least 3 cm on the trunk. Their findings are published in the manuscript “The effect of a bolus dose of intravenous lidocaine on the MAC of sevoflurane: A prospective, randomized, double-blinded, placebo-controlled trial.”
Ninety patients received placebo, 0.75 or 1.5 mg•kg-1 intravenous lidocaine as a single bolus over a time period of 30 sec 3 min before skin incision. The “up and down” adjustment of ET sevoflurane to determine MAC was used. On average, MAC was reduced by 0.23% after 1.5 mg•kg-1 intravenous lidocaine; no effect was observed when 0.75 mg•kg-1 intravenous lidocaine was utilized.
Lidocaine injection was done after a bolus at a single time point; thus, peak effect may have been missed. Effect site concentration may also have varied. Though more robust effects of lidocaine on MAC have been seen in animals, doses higher than are commonly used were studied. As noted in an OpenAnesthesia column on MAC reduction with lidocaine, “Studies of IV lidocaine as a MAC sparing agent in humans are sparse.”