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Sir,

The postoperative recovery period after vitreoretinal surgery can be quite painful and the degree of pain experienced is often related to the duration of the surgical procedure (Fekrat et al. 2001). Secondary analgesia has been noted to be necessary after subtenon ocular anaesthesia (Kwok et al. 1999). However, little has been written about subtenon infiltration analgesia given at the end of vitreoretinal surgical procedures.

Subtenon infiltration of local anaesthetic is a relatively safe and easy procedure (Kwok et al. 1999). Hence we designed a prospective, randomized, double-blind pilot study to assess the efficacy of subtenon Bupivacaine 0.75% infiltration analgesia when used at the end of a surgical procedure to control postoperative pain. All patients undergoing vitreoretinal surgery under a standardized general anaesthetic, between January and April 2002, were selected. All the patients had pre-emptive analgesia with intramuscular Ketoprofen. They were told that they may or may not receive an injection of a pain-killing substance on completion of the surgical procedure and informed consent was obtained. Each patient was assigned to receive either 3 ml of Bupivacaine 0.75% or 3 ml of normal saline after completion of the vitreoretinal surgery, before the conjunctiva was sutured.

The patients were randomized and were operated on by a single surgeon (KLG).

A set protocol for postoperative oral analgesia in the recovery period was observed for all patients. This comprised oral Co-dydramol as a first line and oral Oromorph as a second line of medication. Patients' pain levels were recorded on a 3-point scale (mild, moderate and severe) by nursing staff at set intervals. These were at recovery, at 1 hour, at 3 hours and at 6 hours. Pain was classified as mild (requiring no analgesia), moderate (requiring oral Co-dydramol) or severe (requiring oral Oromorph).

Fifteen patients (60%) received subtenon Bupivacaine and 10 (40%) received normal saline (controls). The surgeries included stand-alone external buckling procedures and vitrectomies with or without additional procedures. The duration of surgery varied from a minimum of 75 min to a maximum of 100 min, with a mean of 120 min. The types of surgeries and their duration were almost similar in the two groups.

Four of the 15 patients (27%) receiving subtenon Bupivacaine 0.75% complained of some postoperative pain, which was mild to moderate in nature. Only two of these patients required additional analgesia. Nine of the 10 controls (90%) experienced postoperative pain and all of them needed analgesia. Most of them complained of pain within the first 3 hours after surgery. Five patients complained of severe pain and four of moderate pain. One patient had both nausea and vomiting.

The efficacy of pre-emptive subtenon Bupivacaine 0.5% anaesthesia in retinal surgery was reported by Mahfouz & Nabawi (2002). However, to the best of our knowledge no other publication has documented the effect of subtenon Bupivacaine used after completion of retinal surgery, solely for the purpose of postoperative analgesia.

In our series subtenon Bupivacaine 0.75% proved to be a safe and effective analgesic when used in patients undergoing vitreoretinal surgery under a general anaesthetic.

Although the study groups were small, the results were statistically significant. However, a larger number of patients should be studied to validate the results of this research.

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