Inconsistent Effects of Dexamethasone on Nerve Block Duration

In a randomized controlled trial reported in the British Journal of Anaesthesia, researchers at the University of Copenhagen found that adding dexamethasone to ropivacaine for nerve block prolongation produced mixed results.¹

To increase the duration of peripheral nerve blocks for postoperative pain, an adjuvant may be administered in addition to the local anesthetic. The efficacy of perineural dexamethasone for this purpose has been supported by various studies, including findings that it extends analgesia for up to 10 hours vs placebo.²

However, it is unclear whether dexamethasone exerts its effects via local or systemic mechanisms of action. “Considering the potential augmentation by perineural dexamethasone on local anaesthetic-induced neurotoxicity… and the finding that dexamethasone does not directly affect the action potentials in A- and C-fibres… this enigma needs to be resolved,” wrote the authors of the current study.^3,4

To control for systemically mediated effects of perineural dexamethasone, they administered bilateral blocks simultaneously so that both would be equally influenced by systemic effects if present, and any observed differences could then be accounted for by local effects. They hypothesized that adding dexamethasone to ropivacaine would prolong block duration, and that this effect would be mediated by local mechanisms of action.

Each participant in the sample of 20 healthy adult male volunteers received bilateral saphenous nerve blocks. One leg was injected with ropivacaine 0.5%, 20 ml plus dexamethasone 2mg, and the other leg was injected with ropivacaine 0.5%, 20 ml plus saline. Block duration as assessed by temperature discrimination was the primary outcome.

According to the results, there was not a significant difference in block duration between the 2 treatments, as assessed by the primary outcome measure (estimated median difference 1.5 h, 95% confidence interval, -3.5 to 0, P =.050). There was a significant difference in block prolongation for all secondary outcomes–which included duration assessed by mechanical discrimination; pain response to tonic heat stimulation; warmth detection threshold (WDT); and heat pain detection threshold (HPDT)–in the leg injected with dexamethasone. However, median differences were < 2.0 h. Block duration was prolonged for at least 2 hours in the dexamethasone leg in only 8 of the participants. 

The finding that block duration was shorter in the leg receiving dexamethasone in some participants indicates that the “peripheral effect of dexamethasone is very variable, and in some subjects, there may be no peripheral effect, making other factors for duration dominant…,” the authors wrote. While block duration varied between subjects, the use of bilateral injections in the present study help to clarify that “differences between our groups were not influenced by systemically mediated analgesia but solely reflect the local effect of dexamethasone as an adjuvant to ropivacaine.”

Summary and Clinical Applicability

The addition of dexamethasone to ropivacaine for prolonged block duration produced highly variable results in healthy subjects.

Limitations and Disclosures

Limitations: Since the study only assessed sensory block, a motor effect of dexamethasone cannot be ruled out. Additionally, the use of a higher dose may have produced more pronounced results that the authors found.

Disclosures: Dr Jæger reports that he has received speaker’s honorarium from Smiths Medical, MN, USA. Dr Jæger and Dr Grevstad report that they have received funding for a clinical study from Smiths Medical, MN, USA

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References

1. Jæger P, Grevstad U, Koscielniak-Nielsen ZJ, Sauter AR, Sørensen JK, Dahl JB. Does dexamethasone have a perineural mechanism of action? A paired, blinded, randomized, controlled study in healthy volunteers. Br J Anaesth. 2016; 117(5):635-641.
2. De Oliveira GS Jr, Castro Alves LJ, Nader A, Kendall MC, Rahangdale R, McCarthy RJ. Perineural dexamethasone to improve postoperative analgesia with peripheral nerve blocks: a meta-analysis of randomized controlled trials. Pain Res Treat. 2014; 2014:179029.
3. Williams BA, Hough KA, Tsui BY, Ibinson JW, Gold MS, Gebhart GF. Neurotoxicity of adjuvants used in perineural anesthesia and analgesia in comparison with ropivacaine. Reg Anesth Pain Med. 2011; 36: 225–230.
4. Yilmaz-Rastoder E, Gold MS, Hough KA, Gebhart GF, Williams BA. Effect of adjuvant drugs on the action of local anesthetics in isolated rat sciatic nerves. Reg Anesth Pain Med. 2012; 37: 403–409.