Somebody else’s nervous system

R. Shankar1, P. D. W. Fettes2 and J. A. W. Wildsmith2

1 Bedford, UK and 2 Dundee, UK

Editor—The editorial by Fettes and Wildsmith is informative and interesting.1 I would like to highlight a particular problem with the combined spinal epidural technique (CSE). In the conventional spinal anaesthetic procedure, the needle is supported by the interspinous ligament and ligamentum flavum, even if it is introduced through an introducer, adding stability to the needle. In CSE, the very fine spinal needle is only held by the tissues of the epidural space, dura and arachnoid membranes. There is a risk of needle movement while attaching the syringe and injecting the local anaesthetic, increasing the risk of nerve damage. Thus, it is possible for the needle to come into contact with a nerve towards the end of the injection, after it has been bathed with local anaesthetic, without eliciting paraesthesia.

R. Shankar

Bedford, UK

Editor—We would like to thank Dr Shankar for his kind comments, and the journal for the opportunity to reply. Dr Shankar raises another concern about the use of the combined spinal epidural technique (CSE) which, although not our primary subject, does give rise to some concern. We agree that, because of the lack of ligamentous support, there is greater scope for the spinal needle to move during CSE. However, it should always be remembered that this possibility still exists with the standard single needle spinal. The main point which we wished to make in our editorial,1 was that any instrumentation of the vertebral canal should be conducted with the utmost care.

Dr Shankar’s second point is interesting and may be at least partly valid. Local anaesthetics penetrate the nerve rootlets very quickly in the subarachnoid space, where there are no nerve sheaths, and movement at the end of injection could well lead to damage here without contemporary symptoms. However, injection of local anaesthetic takes only a few seconds, so whether the drug would have time to affect the spinal cord itself is another question. Thus Dr Shankar’s point is unlikely to be relevant to the cases described by Dr Reynolds,2 which triggered our editorial. All seven patients felt pain on insertion of the spinal needle, and six had evidence of spinal cord damage on subsequent magnetic resonance imaging scan.

P. D. W. Fettes

J. A. W. Wildsmith

Dundee, UK

References

1 Fettes PDW, Wildsmith JAW. Somebody else’s nervous system. Br J Anaesth 2002; 88: 760–3[Free Full Text]

2 Reynolds F. Damage to the conus medullaris following spinal anaesthesia. Anaesthesia 2001; 56: 238–47[ISI][Medline]





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