Reducing pain during postop pediatric strabismus surgery

Bupivacaine can reduce pain in children undergoing strabismus surgery, said Laura B. Enyedi, MD. She and her two co-authors, David K. Wallace, MD, MPH, and Guy de Lisle Dear, MBBCHIR, discussed the off-label use of anesthestic drugs in the pediatric population.

In one study on strabismus surgery, Dr. Enyedi said upwards of 50% of pediatric patients “experience clinically significant pain” in the postop period.

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“Pain is bad for the patient, for the healthcare system, and for the doctor,” she said. “It’s associated with discharge delays, contact after discharge, patient and parental dissatisfaction, as well as long-term post-operative behavioral changes.”

The best pain control is a multimodal approach that consists of narcotics and non-narcotic pain relievers including nonsteroidal anti-inflammatories, acetaminophen, and local anesthetics, she said.

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Previous randomized studies on the pediatric population have evaluated everything from drugs to delivery methods and used a variety of outcome measures. But with conflicting results, no clinical consensus has emerged to determine what benefit-if any-can be gleaned with local anesthetics on pain control.

Dr. Enyedi’s group evaluated whether local anesthetics, either topical or sub-tenons, given at the end of strabismus surgery, reduce post-operative pain in children of ages 12 months to less than 8 years. The randomized, double-masked study enrolled 50 patients already scheduled for strabismus surgery at the Duke Eye Center (NC). Patients were randomly assigned to one of three groups: sub-tenons control with topical anesthetic, sub-tenons anesthetic with topical control, and a sub-tenons control with a topical control, she said. Of potential interest, the wounds were both fornix- and limbal-based.

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Assessment

“Our drugs included a topical anesthetic, which is lidocaine hydrochloride 3.5%, actin gel, a sub-tenons anesthetic, bupivacaine 0.5%, and two controls, a topical control, hypromellose 0.3%, which is Genteal Severe Dry Eye Relief, and the sub-tenons control was balanced salt solution,” she said. “All patients received the sub-tenons clear liquid via a blunt cannula through the surgical wound at the end of surgery and a topical clear gel applied to the surface of the eye at the end of surgery.”

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The researchers assessed pain at multiple points: every 5 minutes postop for the first 30 minutes; then every 15 minutes for the next 2 hours; then hourly until the patient was discharged.

Using the Children's Hospital Eastern Ontario Pain Scale (CHEOPS), a “widely accepted, validated, objective pain scale that assesses pain in young children by looking at several items including the cry, the facial expression, the child's verbalization, the torso position, what the child is doing, touching the wound, and the leg position,” Dr. Enyedi said scores ranged from 4 to more than 14.

“A score of greater than 4 on this scale is considered an indication of pain,” she said.

Results

The primary outcome in this study was the average pain score over the first 30 minutes, Dr. Enyedi said, with secondary pain outcomes including the peak pain score in the first 30 minutes, the total average pain score over the entire assessed period until discharge, and the number of times the pain score was above 6. Other secondary outcomes included total narcotic use, postoperative nausea and vomiting, time to discharge, and negative postoperative behaviors.

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Baseline characteristics for the three groups were similar in terms of age, gender, number of muscles operated, number of incisions, as well as limbal versus fornix incisions.

“There was a difference in the distribution of bilateral cases, with the sub-tenons bupivocaine group having fewer bilateral cases than either the topical lidocaine or control groups,” she said, adding that bilaterality might be a factor associated with pain.

Nonetheless, there was a statistically significant difference with the sub-tenons Bupivocaine group having a lower pain score than the control group in the first 30 minutes. The bupivacaine group also had lower pain scores than the lidocaine group, but the difference did not reach statistical significance, she said.

A re-assessment of pain scores in the bilaterality group dissipated the statistical differences between the control and bupivacaine groups, she said.

Clinical interpretations

Clinical interpretations

An “important confounding variable” the group had not evaluated was the potential differences in pain levels when there are horizontal vs. vertical or oblique muscles, Dr. Enyedi said in response to a discussion on the paper.

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“There may be differences in the fornix-based surgery vs. limbal-based surgery, or maybe differences among surgeons,” she said, but noted the sample size was too small to rule out any differences that might exist.

Because her group delivered bupivacaine with a blunt cannula into the surgical wound to minimize the risk of injecting into the muscle, “there were no complications or changes notes, but we were not assessing for that potential variable directly.”

Regarding the dose levels, Dr. Enyedi noted she chose the bupivacaine 0.5% to ensure she did not over-deliver the drug to the patient and create a sub-Tenon’s prolapse.

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Laura B. Enyedi, MD

E: Enyed001@mc.duke.edu

This article was adapted from Dr. Enyedi’s presentation at the 2015 meeting of American Academy of Ophthalmology. Dr. Enyedi received grant support from the Pediatric Eye Disease Investigator Group. She reported no other financial disclosures.