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Reply to Dr Tilakaratna
- Gary M Stocks, Felicity Plaat (7 December 2006)
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Why doesn't fluid spill out after "epidural volume extension" ?
- Prasanna N Tilakaratna (27 November 2006)
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Role of CSE in Elective Caesarian Section
- Andrew Stapleton (12 October 2005)
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Gary M Stocks , Felicity Plaat
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Thank you for giving us the opportunity to respond to Dr Tilakaratna’s query about the occurrence of fluid spill back from the Tuohy needle when saline is injected during epidural volume extension, (EVE). In all previous studies of EVE the fluid is injected into the epidural space via the epidural catheter and the problem of fluid leakage was not documented. When we began employing this technique we decided to inject directly through the Tuohy needle for two reasons. Firstly the epidural sets we use contain relatively soft catheters that occasionally cannot be inserted and a second attempt with a stiffer catheter is required. Previous studies have shown the effect of EVE to be time dependant and by injecting via the Tuohy we avoided this potential delay. Secondly a study by Verniquet [1] showed that flushing the Tuohy in this way reduced the incidence of a bloody tap with the catheter – thus we decided to kill two birds with one stone! Leakage of fluid back through the Tuohy needle does occasionally occur, but when it does we simply occlude the end with a thumb for no more than a couple of seconds after which the flow ceases. However in our experience this happens infrequently and we speculate why this might be. Hoffmann et al [2] demonstrated that the degree of protrusion of a spinal needle beyond the tip of a Tuohy needle required to successfully puncture the dura ranges from 2.5-15 mm suggesting that there is wide variation in the size of the lumbar epidural space. We speculate that this will also cause variations in epidural space compliance. Just as this might explain why the same volume of EVE can have a variable effect on eventual block height achieved, variations in compliance might also explain why, in some, fluid may leak out of the Tuohy but in others it does not. In this context patient positioning may also be important in affecting epidural compliance. We find fluid leak to be more common when patients are placed in the sitting position during the CSE procedure. However in our study, all patients were placed in the lateral position and leakage was not a significant problem. The infrequency of fluid leakage might also be related to the position of the tip of the Tuohy needle with-in the epidural space. Fat, nerves and blood vessels are all present and it is quite possible that any of these may occlude the end of the needle and prevent leakage of fluid. Although Dr Tilakaratna speculates that to guarantee intrathecal compression there is a need to ‘fill to spill’, the implication from this is that unless fluid does leak from the Tuohy needle no compression of the dural sac can occur. As most EVE studies have injected volumes via the epidural catheter it is impossible to say whether this is correct, however clinical and radiological evidence cited in our paper demonstrates that an EVE effect can be obtained with volumes of 5-10mls and in our experience this does not result in spill. Dr G M Stocks Dr F Plaat Consultant Anaesthetists Queen Charlotte’s and Chelsea Hospital, London, UK. References 1. Verniquet AJW. Vessell puncture with epidural catheters. Anaesthesia 1980; 35: 660-662 2. Hoffmann VL, Vercauteren MP, Buczkowski PW, Vanspringel GL. A new combined spinal-epidural apparatus: measurement of the distance to the epidural and subarachnoid spaces. Anaesthesia 1997; 52: 350-5. Conflict of Interest:None declared |
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Prasanna N Tilakaratna, SpR Anaesthetics Royal London Hospital, London, UK
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I read with great interest the article "Effect of epidural volume extension on dose requirement of intrathecal hyperbaric Bupivacaine at Caesarean section" [1]. I have been perplexed about a certain aspect of "epidural volume extension (EVE)" and hope the authors can shed light on it. It is purported that the mechanism of EVE is that it fills the epidural space with liquid which results in compression of the subarachnoid space leading to the local anaesthetic in it to be pushed upwards. On the few occasions I have done EVE, I have often wondered as to why doesn't the injected fluid return back out of the Tuohy needle. The Tuohy needle does not have a one way valve and its oblique opening precludes the dura from abutting against it and acting as a valve either. With fluid under pressure, one would expect some of it to track back out the Tuohy needle. I would like to ask the authors (and others practicing EVE) if , during the study , they found a significant back flow out the Tuohy after they injected the 7 mls of saline. If they did not observe backflow, then is it possible that more volume is necessary to cause compartmental compression? Perhaps it might be interesting to study the effects of doing EVE with enough saline to cause a backflow out of the Tuohy needle (a "fill to spill" technique) and thus guaranteeing compartmental compression. However, this would have to be done cautiously as fluid boluses into the epidural space are known to have caused retinal venous haemorrhage [2]. I would also like take this opportunity to congratulate the authors for their interesting study. References: 1. Beale N, Evans B, Plaat F, Columb MO, Lyons G, Stocks GM. Effect of epidural volume extension on dose requirement of intrathecal hyperbaric bupivacaine at Caesarean section. Br J Anaesth 2005; 95: 500–503 2. Clifford G. Complications of Epidural Corticosteroid Injections. Topics in Pain Management 2006; 21(11):1-6 Conflict of Interest:None declared |
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Andrew Stapleton, Anaesthetist None
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Would the authors agree that the data presented in their elegant study supports the following hypothesis? "Where a healthy woman presents for an elective caesarian section where a pencil point needle is used to administer a dose of spinal hyperbaric bupivocaine equaling or exceeding 8mg together with 25mcg of fentanyl there is no indication for a Combined Spinal Epidural technique?" Andrew Stapleton Conflict of Interest:None declared |
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