Erskine [1] explains how Luer connection hubs in current spinal needle introducer needles shorten the maximum achievable depth of spinal needles by up to 22 mm. In some patients the introducer needle may therefore prevent the spinal needle reaching the dura. As a solution, he promotes using 'Sise type' introducer needles which, instead of a Luer hub, have a 2 mm thick disc which only minimally limits spinal needle depth. However, a clinical situation I encountered highlights a potential problem that may arise with Sise type introducer needles. I was assisting a colleague giving a spinal anaesthetic to a moderately built patient, in the sitting position, for an elective Caesarean Section. He first inserted the introducer needle (depth 30 mm, Pajunk, Germany) and then was about to insert the spinal needle when I noticed cerebrospinal fluid appear at the hub of the introducer needle. Because the introducer needle had a Luer hub, we were able to use it as a 'short spinal needle' and local anaesthetic was injected via it, resulting in a successful spinal block. Had we used a Sise type introducer needle, we would not have been able to do this as it does not have a Luer hub and the patient would have had to be subjected to a repeat procedure with a new needle. Therefore, though the Sise type introducer may help when the dura is deep, it will be unsuitable when the dura is unexpectedly superficial. There are similar reports in the literature of the use of introducer needles as spinal needles [2, 3]. However, it is difficult to estimate if this occurs frequently enough in clinical practice to become an impediment to the widespread use of Sise type introducer needles.

References:

1. Erskine RJ. Assessment of a new disposable introducer for spinal needles. Anesthesia 2008; 63: 1238–40.
2. Loader J. Dural puncture with an introducer needle. Anaesthesia 2008; 63: 326–7.
3. Malaiya AK, Kulkarni A, Reynolds F. Dural puncture with the introducer of a 26 gauge atraumatic spinal needle. International Journal of Obstetric Anesthesia 1995; 4: 257.