Neuromuscular monitoring and the AAGBI 2016 monitoring guidelines.

We commend the authors for the recently published update of the AAGBI monitoring guidelines 1, and the continued drive to enhance the safety and quality of anaesthesia delivery. The guidance states “a measure of neuromuscular blockade, using a peripheral nerve stimulator, is essential for all stages of anaesthesia when neuromuscular blocking drugs are administered. This is best monitored using an objective, quantitative peripheral nerve stimulator. Ideally the adductor pollicis muscle response to ulnar nerve stimulation at the wrist should be monitored. Where this is not possible, the facial or posterior tibial nerves may be monitored”. While the facial nerve may be monitored, we feel it is important to highlight the potential pitfalls of this site, and that it is not as reliable as ulnar or posterior tibial nerve monitoring. The two muscles innervated by the facial nerve that are suited for neuromuscular monitoring are the orbicularis occuli (eyelid closing) and the corrugator supercilii (draws medial end of eyebrow downwards). However, due to the proximity of the neural plexus, the risk of direct muscle stimulation rather than nerve stimulation is very high, potentially leading to false interpretation. Additionally, it is well recognised that the twitch response of the orbicularis occuli recovers quicker than the adductor pollicis. The clinical relevance of this is highlighted in a study by Thilen et al. which showed that patients who had monitoring of eye muscles had a significantly greater incidence of residual paralysis than those monitored at the adductor pollicis 2. Indeed, the paper by Hemmerling et al. highlighted in the guidelines to support the statement for the interchangeable site of monitoring actually states “more peripheral muscles (e.g. adductor pollicis) need to be monitored in order to determine timely recovery of neuromuscular block” 3. We agree that the use of a quantitative peripheral nerve stimulator is the gold standard and what we should all strive to have routine access to this over the coming years 4. However, this is currently not the case. Therefore, we have concerns that mandating the use of a nerve stimulator, while highlighting the facial nerve as an alternative site of monitoring and without the above caveats, could lead to incidents of postoperative residual curarisation. This is likely to be confounded when anaesthetists unfamiliar with this site feel compelled to use it, but assume it can be managed in the same way as ulnar nerve monitoring.