A meta-analysis confirms that a continuous femoral nerve block (FNB) produces longer-lasting pain relief than a single-injection block after total knee arthroplasty (TKA). The findings were presented at the 2014 World Congress on Pain, in Buenos Aires, Argentina.
These results were also published earlier this year as part of a Cochrane Review analyzing the effectiveness of FNBs in reducing acute pain after TKA (Cochrane Database Syst Rev2014;5:CD009941). The authors determined that patients had statistically significantly lower levels of pain at rest and pain on movement 24 and 48 hours after analgesia for continuous compared with single-injection block.
The comparison made by the team involved four randomized controlled trials, in which a total of 272 patients undergoing TKA were enrolled (Reg Anesth 1996;21:292-297; Anesth Analg 2006;102:1234-1239; Korean J Anesthesiol2010;58:468-476; and J Arthroplasty 2013;28:608-613). The researchers found that each of the four studies had somewhat different methodologies, including patient selection, and some risk for bias.
The researchers converted the pain outcomes to a scale from zero to 10. The summary statistic used for the analysis was mean differences (MD), whereas the Cochrane review used the standardized mean differences (SMD).
“MD is a more intuitively understandable summary statistic for clinicians,” noted Ee-Yuee Chan, PhD, the lead author of the poster and the Cochrane review, as well as the 2013 paper that was one of the four included in the meta-analysis. Dr. Chan participated in the review while she was completing her PhD degree at the Faculty of Health Sciences, University of Sydney, Australia, and is now senior nurse researcher, Tan Tock Seng Hospital, in Singapore.
The analysis showed high heterogeneity between studies with respect to measurement of pain at rest at 24 hours (I2 = 77%), but nonetheless the mean difference in pain at rest at 24 hours between continuous and single-shot FNB was statistically significant at –1.00 (95% confidence interval [CI], –1.90 to –0.10). This represents a mean 1-point greater reduction in pain for continuous versus single-injection FNBs. The heterogeneity between the four studies with respect to measurement of pain on movement at 24 hours was low (I2 = 19%) and the mean difference was again significant, with a value of –0.89 (95% CI, –1.43 to –0.36). This represents a mean 0.89-point greater reduction in pain.
Significant differences were also seen at 48 hours, with mean differences of –1.41 (95% CI, –2.63 to –0.20) and –1.12 (95% CI, –2.04 to –0.21) for pain at rest and pain on movement, respectively. Continuous FNB also was associated with less opioid use than single-shot FNB at 24 and 48 hours.
Stavros Memtsoudis, MD, PhD, clinical professor of anesthesiology and public health, Weill Cornell Medical College, in New York City, who was not involved in the study, was contacted byAnesthesiology News for comment. Dr. Memtsoudis said the findings are not surprising because single injections tend to wear off in 24 to 48 hours. He also said it remains to be seen whether recently available long-acting local anesthetic formulations will be approved for perineural use to prolong the action of single-shot blocks.
“But one also has to consider the potential downsides of prolonged catheter-driven peripheral nerve block [PNB]. Some have suggested it may increase fall risk,” Dr. Memtsoudis said. “Thus, the use of catheter assistance [which is required for continuous analgesia with PNBs] has to be judged in terms of risks and benefits, like everything we do in medicine.”
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