A METHOD FOR DETERMINING THE EFFICIENCY OF LOCAL ANESTHESIA

¹ Section of Dentistry, Mayo Clinic and Mayo Foundation, Rochester, Minn.

A neurophysiologic method was designed for study of the four parameters of local anesthesia, namely (1) onset, (2) onset of complete anesthesia, (3) initial return of nerve activity, and (4) complete return of sensory nerve activity, and was tested on 27 cats. The latter were prepared by insertion of recording electrodes into the left gasserian ganglion and two stimulating needle electrodes into the left maxillary canine fossa. Alterations in the action potential of the nerve were recorded on a quantitative and qualitative basis.

Procaine hydrochloride and lidocaine hydrochloride in 1 and 2 per cent solutions and in doses of 2, 4, and 8 minims were the test solutions. These were injected 1 cm. posterior to the stimulating electrodes.

The onset of complete anesthesia was found to be hastened with an increase in volume of solution injected. This was true for both procaine hydrochloride and lidocaine hydrochloride. The onset of complete anesthesia, however, was generally found to be more rapid with lidocaine hydrochloride than with procaine hydrochloride.

Lidocaine hydrochloride in 2 per cent solution produced complete anesthesia for the longest period. This was true of doses of 2, 4, and 8 minims. The duration of anesthesia was greatest also when a 2 per cent solution of lidocaine hydrochloride was used. It was two to three times greater than with 1 per cent solution of lidocaine hydrochloride or with 2 per cent solution of procaine hydrochloride. An increase in concentration and volume resulted in greater duration of anesthesia.

Two per cent procaine hydrochloride was more effective than 1 per cent procaine hydrochloride. A finding of considerable interest was that 1 per cent lidocaine hydrochloride was more efficient anesthetically than 2 per cent procaine hydrochloride.

This study indicated that the neurophysiologic method employed is adapted to the objective evaluation of the action of local anesthetics.