Extradural block. Confirmation of the injection site by X-ray monitoring.

X-ray monitoring was used to confirm the accuracy of extradural block in 100 patients who attended the Pain Relief Clinic for treatment of a variety of different conditions. A Tuohy needle was introduced by the central or paramedian approach and conventional physical signs, notably loss of resistance, used to identify entry into the extradural space. A radio-opaque dye was introduced prior to the analgesic solution, to display the injection site. X-ray screening confirmed the accuracy of the block in 83 patients, but unexpectedly in 17 the point of the needle was either just outside the spinal canal or only partly in the extradural space. There was no difficulty in correcting the needle position with the X-ray facilities available. Imprecise needle siting is only partially explained by technical problems. Imprecise siting of the needle may be responsible for at least some cases of inadequate analgesia or unexpected complications. In our view X-ray confirmation of site is essential for difficult extradural blocks, or when neurolytic solutions are introduced into the spinal canal. It may also be useful in teaching and research.