1. Adjuncts to Peripheral Nerve Blocks
Mark Mudarth, MD

2. Objectives Review the evolution of Regional Anesthesia
Recap common peripheral nerve block (PNB) adjuncts
Discuss the findings of “Investigating the Efficacy of Dexmedetomidine as an Adjuvant to Local Anesthesia in Brachial Plexus Block”
Discuss impact on current practice

3. Regional Anesthesia: How did we get here?
Intravenous Regional Anesthesia
Bier Block, 1908
Anatomical Approach
Interscalene, early 1900s
Brachial Plexus
Nerve Stimulation
Popularized in the 1980s
Ultrasound Guided
Single shot and perineural catheters
Highest rates of success and greatest safety

4. Facilitation of block quality and duration
Despite improvements in safety, there exist risks associated with PNBs
Nerve damage
Local Anesthetic Systemic Toxicity (LAST)
Diaphragm dysfunction
Pneumothorax
Therefore, numerous adjuvants have been evaluated to provide the following
Faster onset
Slowed absorption
Prolonged analgesic duration
These adjuncts, with a diverse range of mechanisms of action, have been studied with various results
Opioid receptor agonists
Buprenorphine
Morphine
Fentanyl
Vasoactive agents
Epinephrine
Alpha – 2 agonists
Clonidine
Dexmedetomidine
Anti-Inflammatory agents
Dexamethasone

5. Common adjuncts Opioid Receptor Agonists
Buprenorphine, Morphine, Fentanyl
Study data shows prolonged analgesic duration but at the risk of known opioid-induced side effects
Pruritus, nausea, and vomiting
Additionally there are in vitro studies that have shown opioids to have some neurotoxic potential
Vasoactive adjuncts – Epinephrine
Believed to prolong duration by decreasing LA absorption
May decrease the likelihood of LAST
Can help detect an intravascular injection
Data shows minimal change in duration of analgesia when used with ropivacaine
Shown to compromise endoneural blood flow

6. Common adjuncts Vasoactive adjuncts – Clonidine
Provides block prolongation via hyperpolarization of cation channels on the nerve
Significant side effect profile that includes:
Hypotension
Bradycardia
Syncope
Inconsistent results in studies make it hard to determine its role
Vasoactive adjuncts – Dexmedetomidine
An alpha-2 agonist with 7x the affinity of clonidine, causes prolonged blockade via a hyperpolarization activated cation current
Preventing the nerve from returning to resting membrane potential
Side effects again include hypotension and bradycardia
Possibly neuroprotective, based on rat studies

7. Common adjuncts - Dexamethasone
Shown to prolong block duration, although mechanism not fully elucidate
Has been shown to improve PONV
There is concern for neurotoxic potential, especially in vitro
Perineural
Intravascular
Suppressed excitability of nociceptive C fibers
Some vasoconstrictive properties reducing LA uptake
Local inflammatory mediator suppression
Peripheral and central anti-inflammatory effects, inhibiting the production of prostaglandins, leukotrienes, and proinflammatory cytokines
Decreased neuropeptide immune response in injured tissue

8. A meta-analysis of RCTs comparing dexmedetomidine’s (Dex) ability to prolong block duration and shorten onset time when used as an adjunct versus local anesthetic alone
Additionally, the authors hoped to gain a better insight into the adverse event profile of Dex
Primary outcomes:
Onset and Duration of sensory and motor blockade
Secondary outcomes:
Duration of Analgesia
Adverse Events
Overall post-op pain at 24 hours follow-up
Post-op analgesic consumption

9. Study construction Data Management and Extraction
Assessment of Methodological Quality and Risk of Bias
Statistical Analysis and Measurement of Treatment Effect
Assessment of Heterogeneity
Assessment of Publication Bias

10. Results: Sensory Block Onset and Duration

11. Results: Motor Block Onset and Duration

12. Results: Analgesia, Analgesic Consumption, and Pain @24 hours
Unfortunately, given the varied choices of consumable analgesics, an estimated effect on Total Analgesic Consumption could not be constructed
Only 3 studies allowed for statistical pooling regarding pain at 24 hours, and there was no significant difference found with the addition of dexmedetomidine

13. Adverse Events: Hypotension & Bradycardia

14. Results: In Summary

15. Where do we go from here?
Is there utility in extending the duration of our blocks?
Williams et al published that each additional hour of analgesia reduced pain scores by .03 units
In regards to Dexmedetomidine, there may be benefit to its use to help prolong block duration in the diabetic population, especially given its efficacy noted with Ropivacaine
In the non-diabetic population, especially those at risk for PONV, dexamethasone can be an appropriate adjunct for prolonging analgesic duration

16. Questions? References:
Abdallah et al, Intravenous dexamethasone and perineural dexamethasone similarly prolong the duration of analgesia after supraclavicular brachial plexus block: a randomized, triple-arm, double-blind, placebo-controlled trial. Reg Anesth Pain Med. 2015 Mar- Apr;40(2):
Bailard et al, Additives to local anesthetics for peripheral nerve blocks: Evidence, limitations, and recommendations. Am J Health Syst Pharm. 2014 Mar 1;71(5):
Brattwall et al, Upper extremity nerve block: how can benefit, duration, and safety be improved? An update. F1000Res. 2016 May 18;5. pii: F1000 Faculty Rev-907
Hussain et al, Investigating the Efficacy of Dexmedetomidine as an Adjuvant to Local Anesthesia in Brachial Plexus Block: A Systematic Review and Meta-Analysis of 18 Randomized Controlled Trials. Reg Anesth Pain Med. 2017 Mar/Apr;42(2):
Kirksey et al, Local Anesthetic Peripheral Nerve Block Adjuvants for Prolongation of Analgesia: A Systematic Qualitative Review. PLoS One. 2015 Sep 10;10(9):e
Leurcharusmee et al, A Multicenter Randomized Comparison Between Intravenous and Perineural Dexamethasone for Ultrasound-Guided Infraclavicular Block. Reg Anesth Pain Med. 2016 May-Jun;41(3):
Rosenfeld et al, Perineural versus intravenous dexamethasone as adjuncts to local anaesthetic brachial plexus block for shoulder surgery. Anaesthesia. 2016 Apr;71(4):380-8.