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Hanging drop technique for high thoracic epidurals
- Tim Strang, Manjit George (9 November 2005)
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Tim Strang, Consultant Cardiac Anaesthetist South Manchester University Hospitals NHS Trust, Manjit George
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It is with interest that we found the recent article on incidence of lower thoracic ligamentum flavum midline gaps by Lirk et al.(1) The Loss of Resistance (LOR) technique is most commonly used to identify epidural space in the lower thoracic and lumbar regions. In principle, a midline gap could thus impede the LOR encountered using the median approach.(1) As we use the Hanging drop(HD) technique , we thought this letter might be of interest. Our unit undertakes about 200 thoracotomies per year. Post operative analgesia consists of high thoracic epidurals in 50%. Paravertebral blockade combined with epipleural block is used in the remainder. When inserting epidurals, we favour a high approach (T3/4) with the space identified using the HD technique. The HD technique consists of placing a tiny amount of saline into the hub of the Tuohy needle once the stylet is withdrawn. The epidural space is identified once the meniscus is ‘sucked’ into the hub and it disappears. In awake sitting patients, pressure in the thoracic epidural space is negative relative to the surrounding atmospheric pressure.(2) Using the HD technique, the feel of ligamentum flavum before starting as in LOR (midline approach) is not essential, as one merely has to witness ingress of fluid into the needle once the epidural space has been reached .This is particularly pertinent if there is the potential for ligamentum flavum defects in the midline.(1) Hanging Drop method offers other advantages as well: 1. The problem of holding a needle and heavy syringe full of saline is overcome. One is free to precisely guide the needle with 2 hands, which is technically easier. 2. It is easier to teach a trainee using the “visual” sign of HD rather than the “tactile” confirmation of LOR, as the supervising consultant does not have to appreciate what the trainee feels. When watching the meniscus disappear one is often pre-warned by an inward tenting or pulsation of the meniscus before it disappears into the needle hub. 3. When the epidural space has been identified using HD, if there is any doubt, this can then be resolved by free injection of saline into the space as in the LOR method. 4. When using a LOR technique difficulty with locating the ligamentum flavum may result in inadvertent infiltration of the interspinous space with saline making further palpation of the spinous processes and identification of dural puncture equivocal. This problem is obviously circumvented using the HD technique. Using a high thoracic level of insertion overcomes the difficulties of midline insertions at mid thoracic levels caused by the steep inclination of the spinous processes.(3) Epidurals at high thoracic level has been shown to be effective even for combined abdomino-thoracic procedures.(4) In conclusion, in awake patients needing a thoracic epidural, use of the high HD technique is technically simpler for trainees to learn with the reassurance that nothing is lost, should one have to revert to the more familiar LOR approach. Considering the reports on midline ligamentum flavum gaps and the sub- atmospheric pressures in upper thoracic epidural space, we would consider HD technique more advantageous when compared to LOR technique, for a high thoracic epidural. References: 1) P Lirk, J Colvin, B Steger, H P Colvin, C Keller, J Rieder, C Kolbitsch, B Moriggl: Incidence of lower thoracic ligamentum flavum midline gaps BJA 94(6) 852- 855 2) Philip R Bromage: Epidural Analgesia,1978- W B Saunders Company 3) John P Williams: Thoracic Epidural anaesthesia for cardiac surgery. Canadian Journal of Anaesthesia 49: Supplement 1, R7(2002 4) Vlachtsis H, Vohra A: High thoracic epidural with general anaesthesia for combined off pump coronary artery and aortic aneurysm surgery. J cardio Thoracic Vasc Anaesth 17:226-229, 2003 Conflict of Interest:None declared |
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