We read with interest Fredrickson et al's systematic review of postoperative analgesia for shoulder surgery. The authors point out that an insufficient duration of action is the major limitation of single injection interscalene blocks for such patients. However, due to the choice of search terms, there is no consideration of prolonging these blocks by using adjuvant drugs, such as clonidine, which is as α₂-adrenoceptor agonist and prolongs the action of lidocaine by a peripheral action [1].
 
A number of relevant trials have been published previously. For example, Singelyn et al showed a doubling of the duration of analgesia when clonidine was added to 1% mepivacaine in an axillary brachial plexus block [2]. El Saied et al found a similar effect when clonidine was added to ropivacaine [3], and Hutschala and co-workers when clonidine was added to 0.25% bupivacaine with adrenaline 1:200 000 [4]. A systematic review concluded that clonidine probably prolongs brachial plexus blockade regardless of which approach is taken to the plexus [5]. Most recently, Vieira and colleagues demonstrated a significant increase in sensory duration of interscalene blockade when dexamethasone was added to a mixture of bupivacaine, adrenaline and clonidine [6]. These findings included a reduced requirement for supplementary analgesia in the first 24 hours and also lower pain scores. Of particular interest, clonidine and adrenaline were co-administered with bupivacaine to both control and study group patients, suggesting that these researchers also regard these drugs to be effective as adjuvants.
 
Although the ideal adjuvant to local anaesthetic has not yet been described, the subject is surely worthy of attention in order to obviate the complexit,y and perhaps complications of catheter-based approaches to prolonging sensory blockade.

JN Pratap
T Goroszeniuk
Guy's & St Thomas' Hospitals
London, UK
E-mail: jnpratap@doctors.org.uk

No external funding and no competing interests declared.
 
References

1. Pratap JN, Shankar RK, Goroszeniuk T. Co-injection of clonidine prolongs the anesthetic effect of lidocaine skin infiltration by a peripheral action. Anesthesia and Analgesia 2007; 104: 982-3.
2. Singelyn FJ, Dangoisse M, Bartholomée S, Gouverneur JM. Adding clonidine to mepivacaine prolongs the duration of anesthesia and analgesia after axillary brachial plexus block. Regional Anesthesia 1992; 17: 148-50.
3. El Saied AH, Steyn MP, Ansermino JM. Clonidine prolongs the effect of ropivacaine for axillary plexus blockade. Canadian Journal of Anaesthesia 2000; 47: 962-67.
4. Hutschala D, Mascher H, Schmetterer L, Klimscha W, Fleck T, Eichler HG, Tschernko EM. Clonidine added to bupivacaine enhances and prolongs analgesia after brachial plexus block via a local mechanism in healthy volunteers. European Journal of Anaesthesiology 2004; 21: 198-204.
5. Murphy DB, McCartney CJ, Chan VW. Novel analgesic adjuncts for brachial plexus block: a systematic review. Anesthesia and Analgesia 2000; 90: 1122-8.
6. Vieira PA, Pulai I, Tsao GC, Manikantan P, Keller B, Connelly NR. Dexamethasone with bupivacaine increases duration of analgesia in ultrasound-guided interscalene brachial plexus blockade. European Journal of Anaesthesiology 2010; 27: 285-8.

Dr Pratap correctly highlights the (deliberate) omission from our review of local anaesthetic adjuvant as a potential way around the main limitation of a single injection interscalene block - its limited duration of effective analgesia [1, 2].

Perineural clonidine has been the subject of a recent meta-analysis: "Clonidine added to intermediate or long-acting local anesthetics for single-shot ...plexus blocks prolongs the duration of analgesia and motor block by 2 h" [3]. A two-hour treatment effect in the context of a 12-hour block may be statistically significant, but is clinically irrelevant.  When one also considers the drug error risk and clonidine related side effects [odds ratio] (hypotension[3.6], orthostatic hypotension/fainting [5.0], sedation [2.3]), the risks clearly outweigh the benefits [3].

Perineural dexamethasone is the only adjuvant drug known to have a clinically relevant effect: sensory (analgesic) block has been shown to increase from 14 to 24 h[4]. However, even this effect will not obviate the need for a perineural catheter for painful shoulder surgery (e.g. open procedures, arthroscopic rotator cuff repair, non-reverse total shoulder replacement) as this surgery is well recognised as causing moderate to severe pain for >48 hours in a significant proportion of patients [2].The prolongation of sensory blockade with dexamethasone may justify a re-appraisal of the continuous technique for minor arthroscopic procedures (e.g. labral tears, acromioplasty, resection of lateralclavicle) [5]. However, in addition to prolonging sensory block, dexamethasone also increases motor block, and accumulating evidence now points to an inverse relationship between motor block and patient satisfaction [6,7]. This is particularly relevant for single injection techniques because of their all-or-nothing lack of titratability.

Advances also continue to be made with the continuous technique. Administration of the derived optimal primary bolus dose of ropivacaine is associated with higher patient satisfaction when compared to a traditional higher dose [7]. A dose regimen comprising a low background infusion (2 ml. hr^-1) with patient initiated mandatory boluses has been shown to reduce block related side effects when compared to a higher fusion (5 ml. hr^-1; unpublished data from a completed randomised trial). 

Until we have preclinical data supporting the clinical administration of a perineurally-administered agent that provides prolonged sensory block withoutmotor block, clinical research into different combinations of adjuvant to produce longer acting blockade is unlikely to produce significant improvements in patients' peri-operative experience.

Unfortunately, there is no magic pill for shoulder analgesia. It is sometimes a matter of just biting the bullet and so the conclusion remains: "The most urgent areas for future study are the identification of barriers to continuous interscalene block as an analgesic modality and the subsequent evaluation of strategies aimed promoting its uptake"[2].

M. J. Fredrickson

University ofAuckland

Auckland, New Zealand

E-mail:michaelfredrickson@yahoo.com

Competing interests:research support from the I-Flow corporation (as previous declared). 

References

1. Pratap N. Adjuvants to prolong single injection interscalene block for shoulder surgery. Anaesthesia 2010.

2. FredricksonMJ, Krishnan S, Chen CY. Postoperative analgesia for shoulder surgery: a critical appraisal and review of current techniques. Anaesthesia 2010; 65:608-24.

3. Popping DM, Elia N, Marret E, Wenk M, Tramer MR. Clonidine as an adjuvant to local anesthetics for peripheral nerve and plexus blocks: a meta-analysis of randomized trials. Anesthesiology 2009; 111:406-15.

4. Vieira PA,Pulai I, Tsao GC, Manikantan P, Keller B, Connelly NR. Dexamethasone with bupivacaine increases duration of analgesia in ultrasound-guided interscalene brachial plexus blockade. European Journal of Anaesthesiology 2010; 27:285-8.

5. Fredrickson MJ, Ball CM, Dalgleish AJ. Analgesic effectiveness of a continuous versus single-injection interscalene block for minor arthroscopic shoulder surgery. Regional Anesthesia and Pain Medicine 2010; 35:28-33.

6. Fredrickson MJ, Price DJ. Analgesic effectiveness of ropivacaine 0.2% vs 0.4% via an ultrasound-guided C5-6 root/superior trunk perineural ambulatory catheter. British Journal of Anaesthesia 2009; 103:434-9.

7. Fredrickson MJ, Smith KR, Wong AC. Importance of volume and concentration for ropivacaine interscalene block in preventing recovery room pain and minimizing motor block after shoulder surgery. Anesthesiology 2010 ; 112:1374-81.