EDITOR:
I read with interest a case of total spinal anaesthesia reported by Batra and colleagues [Reference Batra, Sharma and Rajeev1]. I would like to comment on their reasoning for the unusual spread of local anaesthetic leading to total spinal anaesthesia. After a careful review of the events, one cannot resist thinking that it hardly resembles a subdural block.
‘Soon after the administration of the test dose’, their patient complained of dizziness and weakness. This clinical picture is typically due to a subarachnoid injection of local anaesthetic. The block spread with subdural is more like an epidural with much slower onset than subarachnoid block with minimal hypotension. Their patient was unconscious, apnoeic, severely bradycardic and hypotensive ‘within a couple of minutes’, which again confirms that the local anaesthetic was injected into the subarachnoid space.
The epidural catheter, they suggest, might have entered the subdural space through the hole in the dura made during multiple attempts at epidural. It is possible that the catheter might well have entered the subarachnoid space through an unrecognized dural hole made by the Tuohy needle. Although aspiration of cerebrospinal fluid (CSF) through the catheter facilitates identification of subarachnoid placement of the catheter, a negative aspiration does not confirm that the catheter is not in subarachnoid space. It is probably for this very reason that the test doses are so widely practised.
They also suggest that the attempts at spinal anaesthesia could have produced multiple punctures in the dura through which local anaesthetic agents could have seeped into the subdural or subarachnoid spaces. To have a total spinal anaesthesia in such a short time from injecting such a small volume of local anaesthetic (lignocaine 2% 3 mL) into the subdural space in the lumbar region in the sitting position is difficult to imagine from a clinical point of view. It could be argued that the arachnoid mater could be torn, thereby allowing the local anaesthetic to access the subarachnoid space. But again, the pressure from 3 mL of solution is highly unlikely to have been sufficient to have caused the tear allowing the local anaesthetic to enter subarachnoid space.
As to the seepage of local anaesthetic into the subarachnoid space, if the dural punctures made during the spinal attempts are close to the epidural catheter holes, then it is possible for the local anaesthetic injected via the catheter to seep into the subarachnoid space. But it is not clear from the case report whether the spinal attempts were made above or below the level of epidural insertion.
Radiological confirmation by injecting water-soluble contrast media has been suggested to confirm the correct position of epidural catheters by Collier [2]. Furthermore, aspiration of epidural catheter before removal may have provided some further clarifications. However, this information is not provided.
It may be that the dura was unintentionally punctured at epidural attempts, which allowed the CSF to leak out of the subarachnoid space into the epidural space. This may also have been facilitated by dural holes made at subsequent multiple attempts at spinal. This would then lead to a relatively low volume of CSF into which the local anaesthetic test dose could have been injected. The cephalad spread of the local anaesthetic is further facilitated by the mechanical compression of the dura by the CSF in the epidural space.
I would disagree with the authors that ‘the clinical presentation suggests that the local anaesthetic was probably injected subdurally rather than epidurally’. It would be interesting to know what other readers think.
