A reply

We wish to thank Professor Wildsmith for his very relevant enquiry. An aspiration test was performed at the time of the local anaesthetic bolus. However, it was done with a 5-ml syringe and the filter still attached. At the time, the patient was almost completely covered in surgical drapes and positioned supine at the foot end of the operating table. Whilst there was no blood in the visible part of the catheter, there is no way to know retrospectively if blood was aspirated into the distal portion of the catheter. As noted by Professor Wildsmith, the hypotension that followed may well have been the first indication of local anaesthetic toxicity; however, it would be an unusual sign of toxicity in the absence of dysrhythmia. Although less likely in the paediatric population, it may also have been the result of increased sympathetic blockade. A test dose with adrenaline and catheter aspiration are routinely performed here on epidural catheter insertion with a small volume syringe and no filter. It is known that aspiration through a filter is unreliable [1]. Re-aspiration before bolus injection is also routine practice. However, in this case, with an epidural that was presumed to be functioning based on low anaesthetic and analgesic requirements, the aspiration technique was not performed with the filter removed or the use of a smaller syringe. It is of course impossible to know whether performing the pre-bolus aspiration test in what is believed to be an ideal manner may have produced a positive finding that could have averted the ensuing events. Given the subtoxic plasma bupivacaine concentration measured during the arrest, it is possible that the catheter may not have been intravascular at the time of the bolus and that the patient was susceptible to bupivacaine cardiotoxicity for reasons explored in the case report. Certainly, in terms of sensitivity and positive predictive value, no ideal test exists to detect intravascular placement or migration of epidural catheters [2, 3]. Whilst awareness of the limitations and recognised false negatives in the testing of epidural catheters is important, we agree with Professor Wildsmith that all cautionary steps must be taken in the prevention of any potential complication. No external funding and no competing interests declared.