Neurological sequelae after neuraxial anaesthesia in obstetric patients: a reply

We thank Murphy et al. [1] for their interest in our study [2] and for furthering the discussion on timely assessment for prolonged motor blockade after neuraxial anaesthesia. Their concerns about the potential unintended consequence of delaying anaesthetic review from the guideline recommendation of 4–6 h are valid, and we would like to take this opportunity to clarify this matter and our stance on the issue.

We believe any abnormally prolonged motor recovery should prompt immediate review by an anaesthetist, as early intervention allows for the timely management of serious complications. However, in order to conduct the review effectively, one needs to consider what constitutes an abnormally prolonged motor block. A meta-analysis encompassing 11 randomised controlled trials involving 316 patients who received either hyperbaric (n = 6, dose range 8–12.5 mg) or isobaric (n = 5, dose range 6.6–15 mg) intrathecal bupivacaine for caesarean delivery with reported mean motor block durations ranging from 1.3 to 4.2 h [3]. In 10 of the 11 studies, the mean motor block duration was < 4 h. Similarly, Cordrey et al. showed that > 50% of patients had fully recovered motor function by 4 h, following intrathecal hyperbaric bupivacaine 0.5% or epidural lidocaine 2% with adrenaline and bicarbonate [4]. These findings align with data from the 3rd National Audit Project report [5] and McCombe and Bogod [6], which recommend that the absence of sensorimotor recovery by 4 h warrants a thorough evaluation. Based on these data, the 4-h threshold was an appropriate and logical recommendation.

After applying the 4-h threshold, we noticed frequent review triggers and found that motor block recovery often takes longer than that documented in the literature. We hypothesise this may, in part, be related to our frequent use of higher doses (13.5 mg) of intrathecal hyperbaric bupivacaine 0.75%. While this formulation is used widely in North America, we were unable to find motor block regression data specifically evaluating this formulation using the time-to-straight-leg-raise against gravity endpoint at the dose range we utilise. In the meta-analysis by Malhotra et al., aside from two trials that did not report the concentration, all others utilised bupivacaine 0.5% [3], as did the studies cited by the Association of Anaesthetists and Obstetric Anaesthetists' Association guidelines. Consequently, the data used to inform the 4-h guideline recommendation may not be generalisable to our patient population.

For patients who still have motor block after 4 h, magnetic resonance imaging is the only definitive method to determine whether the cause is a neuraxial haematoma. However, with an annual delivery volume of 7000–8000, the sheer number of investigations triggered would overwhelm both our anaesthetic and radiology departments. The regional anaesthesia alert bracelet is an excellent initiative that emphasises patient involvement and autonomy. We agree that it is an innovative and valuable patient safety measure that can supplement, but not replace, our current scheduled nurse-led hourly monitoring, which remains essential for postpartum patients who may become too distracted or fatigued to self-monitor. Furthermore, because the bracelet operates on a time-to-action trigger, setting it at 4 h would still result in a high volume of alerts, leaving our clinical dilemma unresolved.

More research is required on this subject to understand the effects of changing the timing triggers on the early detection of significant neuraxial anaesthesia complications and the use of clinical resources. We urge other centres using intrathecal hyperbaric bupivacaine 0.75% for caesarean deliveries in similar dose ranges to confirm our findings.