Obtaining fluid samples and measuring intrathecal pressure may require different approaches

EDITOR—Broadley and Fuller describe methods to reduce the incidence of postdural puncture headache in diagnostic neurology.1 They claim that it is necessary to use large bore spinal needles in order to collect adequate volumes of cerebrospinal fluid and accurately measure intrathecal pressure.

With regard to the first point, the authors state that the time taken to collect 2 ml of cerebrospinal fluid is up to 6 minutes when fine needles are used. Aseptically aspirating cerebrospinal fluid through a fine needle using a 2 ml syringe significantly reduces the time it takes to collect sufficient volumes for analysis. Even so, I think that any extra time taken collecting a suitable sample is worth while if it reduces the incidence of headache.

With regard to the use of 22 gauge needles to measure of intrathecal pressure accurately, Hatfalvi retrospectively reported 4465 cases of spinal anaesthesia in which a 20 gauge sharp bevelled needle was used, which did not seem to be followed by incidence of headache.2 She used a lateral approach for dural puncture, with the bevel of a Quinke needle directed towards the skin. Using an artificial tissue model, she showed that such a tangential approach to the dura, with the bevel directed towards the dura, produces a valvular flap of dura which closes in response to the cerebrospinal fluid pressure when the needle is removed. Her description of the technique is: “From the chosen interspace, the index finger of either hand will slide in a V formation from the midline to the right and left, forming a groove with moderate pressure. The skin wheal should be made at the deepest point, in front of the index finger, followed by the piercing with the spinal needle 2 cm deep with the other hand. The bevel should face the skin …