1 Chelmsford, UK 2 London, UK
EditorWe were delighted to read the review article on Caudal additives in childrensolutions or problems?.1 We have used preservative-free caudal ketamine for over 330 general surgical, urological and orthopaedic paediatric cases in Chelmsford since 1998, providing excellent, prolonged analgesia with no untoward effects.
In the authors summary paragraph they conclude that a combination of ketamine 0.5 mg kg1 and bupivacaine is even more effective [than clonidine 1 µg kg1], providing analgesia for up to 12 h. These additives, they concluded, had superseded the use of caudal opioids and we wholeheartedly concur with these findings.
We were rather disappointed to then read: however, further study and the introduction of ketamine into mainstream clinical practice is limited by the difficulties in obtaining preservative-free ketamine and ongoing concerns about potential neurotoxicity. They also state that the use of caudal additives for day-care anaesthesia is controversial and at present their routine use cannot be recommended. We have obtained preservative-free ketamine 10 mg ml1 (50 mg ampoules) on a named-patient basis since 1998 from Ketamin Curamed (KetamineCuramed Pharma GmbH, Postfach 41 02 29, D-76202 Karlsruhe, Germany).
The authors question the safety of epidural ketamine and quote a paper by Stotz.2 This paper reported a case of a 72-yr-old woman who developed isolated lymphocytic vasculitis of the spinal cord and leptomeninges after a 7 day infusion of ketamine, clonidine, morphine and bupivacaine, although she showed no signs of neurological deficit. The ketamine used was the commercially available ketamine with benzethonium preservative. The patient had an intrathecal catheter in situ for 18 days, initially with morphine 0.12 mg ml1 and bupivacaine 0.25% given at 22.5 ml h1. The dose was then increased to 33.5 ml h1 and the morphine increased to 0.3 mg ml1. During this time, she developed signs of meningitis. Stotz and colleagues concluded that the changes may be related to the preservative benzethonium chloride or the toxicity of the mixture itself.2 With regard to the use of caudal additives for day-care anaesthesia, we are at a loss to understand why the authors think that the addition of preservative-free ketamine to caudal bupivacaine should be controversial. Is it their worry of neurotoxicity or some other long-term side-effect that concerns them?
We feel that the addition of preservative-free ketamine to caudal bupivacaine is not only a good analgesic but should be the method of choice in this type of paediatric case.
N. C. Huddy
K. Kiff
Chelmsford, UK
EditorWe are pleased that Drs Huddy and Kiff enjoyed our recent review,1 and we thank you for the opportunity to reply. With regard to the availability of preservative-free ketamine, we are glad to read the authors ease in obtaining this, albeit on a named-patient basis. This necessarily cumbersome process represents a practical barrier to its more widespread acceptance. As was reported recently,3 preservative-free ketamine is now available in this country and therefore no longer has to be imported directly from Germany. This, we trust, will increase the frequency with which it is used.
We were delighted to hear of yet more evidence, albeit anecdotal, of Drs Huddy and Kiffs positive experiences with the drug as a caudal additive in children and would encourage them to formally report their data to add to the growing, yet still small, body of clinical evidence to support its use.
As regards neurotoxicity, Huddy and Kiff are quite correct in drawing attention to the equivocal aetiology of the only human case report of neurotoxicity associated with epidural ketamine. However, as stated in our review,1 there is animal data of the vacuolation of posterior root ganglia attributable to ketamine, admittedly at high doses.
With regard to the use of caudal additives for day-case anaesthesia, we stand by our original statement and maintain that, at present, their routine use cannot be recommended. The reason for this relates to the potential problems that may arise after discharge as a result of prolonged sensory and motor block, in particular block of thermal sensibility.4 While these problems might also occur with the use of plain bupivacaine, the use of additives such as clonidine and ketamine increases the risk.
We therefore feel it is worth exercising caution rather that advocating its widespread use while the body of clinical evidence tips ever more in favour of caudal ketamine.
M. L. Thomas
D. A. H. de Beer
London, UK
References
1 de Beer DAH, Thomas ML. Caudal additives in childrensolutions or problems? Br J Anaesth 2003; 90: 48798
2 Stotz M, Oehen HP, Gerber H. Histological findings after long-term infusion of intrathecal ketamine for chronic pain: a case report. J Pain Symptom Manage 1999; 18: 2238[CrossRef][ISI][Medline]
3 Martindale M, Worsley M. Caudal additives in childrensolutions or problems? Br J Anaesth 2003; 91: 30030
4 Cooper R. Clonidine in paediatric anaesthesia. Paed Anaesth 2000; 10: 2234[CrossRef][Medline]