A Comparison of the Hydrochloride and Carbon Dioxide Salts of Lidocaine and Prilocaine in Epidural Analgesia

SUMMARY Lumbar epidural blockade has been used in a series of 659 patients to compare the analgesic properties of lidocaine and prilocaine. Solutions of both compounds were compared as hydrochloride salts in 2% and 3% concentration with and without adrenaline 1:200,000. Solutions of base, made soluble by equilibration with carbon dioxide at a pC0 2 of 700 mm Hg were also compared in concentrations of 1.75% for lidocaine and 1.71% for prilocaine. Comparisons were based on measurements of latency, spread of analgesia, intensity of motor blockade and duration of analgesia. The quality of blockade in all the test solutions was increased by the addition of 1:200,000 adrenaline. Prilocaine has a slow latency compared with lidocaine, but in plain solution its duration is longer than that of lidocaine. The 3% hydrochloride solutions have no practical advantage over die 2% solutions for epidural blockade. Analgesia resulting from the C0 2 ‐base solutions is superior in every respect to the blockade produced by equivalent concentrations of the hydrochloride salts.