Aspiration of CSF followed by epidural blockade in labour.

Abstract

Various combinations of positive and negative aspiration and test doses have been suggested to check the correct placement of an epidural catheter [1]. In general, all combinations which include a positive aspiration test for CSF are followed by the assumption that the catheter is in the subarachnoid rather than the epidural space. We wish to report a case which casts doubt on this assumption. A 31-year-old multigravida requested epidural analgesia for labour, which was attempted at the L2/3 interspace using a 16G Tuohy needle. This resulted in a dural tap with free flow of CSF through the needle. The needle was withdrawn and a second attempt was made at the L3/4 interspace. Loss of resistance to saline was achieved and the catheter advanced without difficulty. Aspiration through the catheter prior to administration of the test dose produced 3 ml of CSF (testing positive for glucose). In view of the difficulties experienced it was decided to use this (possibly subarachnoid) catheter to provide analgesia. Bolus doses of 2, 3 and 5 ml of 0.25% bupivacaine over a 45-min period produced good analgesia with evidence of a sensory block (to ethyl chloride) from T10 to L2 dermatomes. Further top-ups of 10 ml 0.25% bupivacaine were subsequently given without incident. Following the first bolus of bupivacaine, and thereafter, it was not possible to aspirate CSF from the catheter. We believe that after the initial dural tap there may have been ‘pooling’ of CSF in the epidural space which was then aspirated through the epidural catheter giving a false positive aspiration test. This case illustrates that following dural puncture, aspiration of CSF from a second epidural catheter is not necessarily indicative of subarachnoid catheter placement, but may result from a correctly placed catheter in the epidural space allowing aspiration of CSF leaking from a previous puncture site. Removing the catheter and replacing it with a further epidural catheter is therefore unnecessary, although it is essential to use small incremental doses in this situation and to observe the patient closely for untoward or exaggerated responses to subsequent doses.