Dilution of Proparacaine in Balanced Salt Solution Reduces Pain of Anesthetic Instillation in the Eye

Author: Brady MD; Hustead RR; RobinsonRH; Becker KE Jr, Department of Anesthesiology, University of Kansas School of Medicine-Wichita 67214

Publication: Reg Anesth 1994 May-Jun;19(3):196-8

BACKGROUND AND OBJECTIVES: Proparacine (P), 0.5%, is often applied topically to the eye to diminish the pain of injection of anesthetic for eye surgery; however, application of 0.5% P itself can cause some degree of discomfort. This study evaluated the use of balanced salt solution to dilute P before instillation in the eye to prevent discomfort.

METHODS: In a double-blinded manner, 42 consenting adults about to undergo cataract surgery were given 0.5% P in one eye and 0.03% P in the other eye. One minute later the same solutions were instilled into each eye. Ten minutes later, 0.5% P was instilled into both eyes. After each instillation the patients were asked to describe the pain in each eye on a 0 to 10 scale.

RESULTS: Those receiving 0.5% as the first drop had a mean score of 1.28, which was greater than the score of 0.09 for the 0.03% P group (P<.01). No one reported pain after the second drop was applied 1 minute later. After receiving 0.5% P 10 minutes later, the group that received 0.5% P reported a mean pain score of 0.09 while those who had received 0.03% P reported a score of 0.76, which was significantly greater than that reported by the 0.5% P group after the 10 minute instillation (P<.01) but significantly lower than the score reported after the first instillation of 0.5% P (P<.05). CONCLUSIONS: Dilution of P in balanced salt solution to a concentration of 0.03% produces a solution that is significantly less painful than 0.5% P and reduces the discomfort of the instillation of 0.5% P.