In Total Shoulder Arthroplasty:
A large, retrospective study from Mayo Clinic has concluded that the addition of clonidine to a single-shot interscalene block does not improve the quality of analgesia in patients undergoing total shoulder arthroplasty.
The study has helped clarify an issue that has had its supporters and detractors. The investigators noted, however, that some clinicians may still choose to supplement blocks with the α2-adrenergic agonist, given its relative lack of side effects.
“We have a busy shoulder practice and had polarized views regarding the use of clonidine as an additive for single-shot, long-acting blocks, whether they be interscalene or any sort of brachial plexus block,” said Adam K. Jacob, MD, associate professor of anesthesiology at the Rochester, Minn., institution.
“And we never really had conclusive evidence one way or the other; people in both camps could cite literature that would support their view, no matter what it was.
“So we simply wanted to provide some objective evidence to inform our practice, so we could try to put the issue to rest. We also see a lot of patients, so we knew that from our single center we could perform one of the larger studies on the subject.”
Minimal Differences Found
To that end, the investigators retrospectively reviewed the medical records of all consecutive adults who underwent total shoulder arthroplasty with an ultrasound-guided, single-injection interscalene block for postoperative analgesia at Mayo Clinic between January 2010 and November 2015.
A variety of data were recorded, including the regional block technique, perioperative medications, pain scores, 24-hour oral morphine equivalents, time to first opioid administration after PACU discharge and perioperative complications.
A total of 1,332 blocks were performed without perineural clonidine and 289 were performed with it during the study period (Table). If a patient received multiple blocks, only the first was included in the analysis.
Although the study was retrospective and has limitations such as the inability to control for all confounding factors or to record all measurements of interest, Dr. Jacob was encouraged by the fact that some potential confounders were largely standardized by institutional practice. “The anesthesiologists all generally use the same approach for performing these blocks,” he noted, “and we limited the data to two surgeons who use nearly identical surgical techniques.”
The two groups were similar on demographics, local anesthetic volume and perioperative opioid administration; the median clonidine dose was 100 mcg (mean, 95 mcg).
As Dr. Jacob reported at the 2016 annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 1354), although clonidine patients experienced a statistically significant decrease in pain (–0.39; 95% CI, –0.13 to –0.64; P=0.003) between three and seven hours after block administration, the difference was not clinically relevant.
“We realize that this was one of those situations where there was a statistical difference, but if you actually look at the raw numbers, you could argue that there was very little clinical difference,” he said. “Because even at its greatest, the difference in pain scores between groups was no more than half a point.”
Furthermore, no differences were found between groups in 24-hour opioid consumption (71.6±6.1 mg for patients who received supplemental clonidine vs. 68.3±2.8 mg for those who did not; P=0.61). Time to first opioid administration was also similar (8.1±0.3 vs. 8.0±0.2 hours, respectively; P=0.80). Although more clonidine patients had intraoperative hypotension (19.4%±1.0% vs. 17.3%±0.4%, respectively; P=0.049), no difference in vasopressor use was found.
Finally, no other differences were observed between groups with respect to adverse events such as intraoperative bradycardia, unexpected ICU admission, stroke or death. The investigators also performed a subgroup analysis wherein they controlled for one surgeon, a fixed local anesthetic volume and clonidine dose; these analyses yielded similar results.
A Change in Viewpoint
Formerly a member of the pro-clonidine camp, Dr. Jacob is now taking a different view of the adjuvant, given the results of this study. “My rationale for using clonidine was probably biased toward that body of literature that said it may be helpful, coupled with anecdotal experience of my patients, who said they didn’t have as much pain when the block wore off,” he explained.
“When you combine that with the fact that it’s a relatively inexpensive additive and the general lack of adverse effects that have been reported, my position always was, ‘Why not add it?’
“Now I’m not insistent on adding it, based on these data,” Dr. Jacob continued. “Because even though we found some statistical differences in pain scores, we really didn’t see any meaningful clinical differences between the two. So now I’ve shifted camps a little bit to say there’s probably no benefit in adding it.”
Chad M. Brummett, MD, was surprised by the results, pointing to a meta-analysis (Anesthesiology 2009;111:406-415) for comparison. “That meta-analysis of 1,054 patients receiving clonidine through randomized controlled trials clearly demonstrated about two hours of efficacy.
“So I think the efficacy of clonidine in peripheral nerve blocks is incredibly well established,” Dr. Brummett continued. “It’s hard to say that a retrospective review of approximately the same number of patients—with all the biases inherent in retrospective reviews—is more informative.”
Dr. Brummett agreed, however, that the jury is out as to whether it makes fiscal sense to add clonidine for such a short analgesic benefit.
“Even with two hours of improved analgesia, some clinicians will still question whether it’s enough to merit the cost or time to add clonidine, especially since clonidine’s vials are not multiuse,” he said. “All told, the question is whether clonidine’s efficacy is clinically meaningful enough for that practitioner to merit the additional cost.”