Abstract
AIMS: To determine the relation between pH of anaesthetic solutions and patient perception of pain with peribulbar injection of local anaesthesia. METHODS: This prospective randomised controlled double blind pilot study involved 60 consecutive patients who received a peribulbar block with either a standard acidic local anaesthetic of 5 ml 2% lignocaine and 5 ml of 0.5% bupivacaine (solution A), or an alkalinised solution composed of the same anaesthetic agents but with a pH of 7.44 (solution B). Before surgery patients were asked to grade the pain of both the preoperative dilating drops and the peribulbar injection using a visual analogue scale. RESULTS: The mean pain scores were similar in the two treatment groups-slightly higher (4.97) in group B who received the buffered solution, compared with group A (4.84) who received the plain solution. The small difference (-0.13, 95% confidence limits -1.6 and +1.3) was not significant. There was, however, a highly significant association between pain threshold ("drop pain") and injection pain levels (p<0.0001). CONCLUSION: This study showed no difference in the reduction in the pain experienced by patients undergoing peribulbar anaesthesia with pH buffered local anaesthetic. The study suggests the importance of "pain threshold" as a confounder and also showed the considerable pain felt by some patients on instillation of the preoperative dilating drops.