Clinical pharmacokinetics of carbonated local anesthetics. II: Interscalene brachial block model.

A double-blind comparison of 1.1% lidocaine carbonate and 1.0% lidocaine hydrochloride was carried out in 30 healthy adult patients undergoing upper-extremity surgery under interscalene brachial plexus block. Epinephrine (1:200,000) was added to both solutions just before injection. As compared to lidocaine hydrochloride, lidocaine carbonate produced, in addition to a 38% reduction in onset time, a remarkable increase in the extent of anesthesia: lidocaine carbonate produced surgical anesthesia of the entire upper extremity including the hand in 87% of the patients, whereas lidocaine hydrochloride produced similar anesthesia in only 53% of the patients. Thus, supplemental blocks were required in 66% of the patients who received lidocaine hydrochloride, whereas they were required in only 25% of those who received lidocaine carbonate.