In response to comments on: No rent is small for migration of epidural catheter into subarachnoid space

Sir,

We are thankful to the learned reader for his constructive analysis of our case report.[1,2] In response to the questions raised, we wish to submit that while the pressure on the epidural needle is always calibrated when performing epidural puncture, it is not so when inserting needle for infiltration of the local anaesthetic agent. On the contrary, the intention is to push the needle and inject local anaesthetic deeper. Covering several mm distance beyond the length of the needle is, therefore, possible, as probably would have happened in our case. We used air to check loss of resistance to identify epidural space. An aspiration check done before injection of the local anaesthetic agent aspirated fluid into the syringe containing local anaesthetic. We could only infer it to be cerebrospinal fluid (CSF) in all probability, and not local anaesthetic which was never injected prior to this point. Aspirated fluid was now mixed with the local anaesthetic agent in the syringe and, therefore, we did not check the temperature and sugar content of the aspirated fluid and also we had not foreseen the events to have preserved the fluid for future analysis. Subsequently, when the fluid was aspirated from the epidural catheter, we did confirm it to be CSF, as mentioned.

We do agree with the suggested possibility that epidural needle could have created a rent in the dura mater and that epidural catheter would have then created a rent higher up in the arachnoid mater and migrated further into the subarachnoid space. However, in this case, our assumption was that the 26-gauge needle in all probability punctured both the dura and arachnoid mater as evidenced by aspiration fluid. Also that 14 cm of epidural catheter was at the needle hub when fluid was seen, the epidural catheter must have just exited the epidural needle (epidural needle + catheter stabiliser = 12 cm). The possibility of the epidural catheter to have migrated into the subarachnoid space through the same rent, therefore, seems more plausible.