Persistent train-of-four fade in myasthenia gravis patients after sevoflurane anaesthesia.

Editor—We read with great interest the article by Nitahara and colleagues showing concentration-dependent inhibitory effects of sevoflurane on neuromuscular transmission in myasthenia gravis (MG) patients which was more prominent in patients with a pre-anaesthetic T4/T1,0.9. In their study, T4/T1 returned to baseline value in all patients at the end of anaesthesia. The importance of monitoring pre-anaesthetic T4/T1 ratio in MG patients has been previously mentioned in a study showing significantly lower atracurium requirements in patients with pre-anaesthetic T4/T1,0.9. We also investigated T4/T1 ratio as a predictor for early extubation in 11 MG patients using sevoflurane and remifentanil without concomitant use of neuromuscular blocking agents. Interestingly, five patients, of whom only one patient showed pre-anaesthetic T4/ T1,0.9, had persistent T4/T1,0.9 at the end of anaesthesia, even when the end-tidal sevoflurane concentration was below 0.3%. Of the five patients, two had pre-anaesthetic T4/T1.0.9, had T4/T1,0.8 and did not meet the extubation criteria (inspiratory force .25 cm H2O and vital capacity of at least 10 ml kg), and could not be extubated in the operating room. These two patients had similar characteristics as the other nine patients, including serum anti-acetylcholine receptor antibody titre, except that they had bulbar symptoms and a more severe grade of MG. Sevoflurane may be a suitable anaesthetic agent for MG patients owing to the concentration-dependent inhibitory action on neuromuscular transmission with rapid reversibility after discontinuation. 2 However, as we observed, persistent fade can occur at the end of sevoflurane anaesthesia, regardless of the presence of preanaesthetic fade, hindering early extubation even when no neuromuscular blocking agents were used. The association of MG severity and recovery of fade needs to be validated in a further study and we recommend monitoring postrecovery T4/T1 ratio as well, during sevoflurane anaesthesia without the use of neuromuscular blocking agents in MG patients to avoid unnecessary risk of respiratory compromise and delay in extubation.