Optimal dose of mivacurium for laser-assisted laryngeal microsurgery: a pharmacokinetic study using closed-loop target-controlled infusion

Purpose:
Mivacurium is a short-acting, non-depolarising neuromuscular blocking agent that provides adequate vocal cord myorelaxation during transoral laser microsurgery. This study aimed to determine the optimal dose of mivacurium by comparing the infusion rate delivered via a closed-loop target-controlled infusion system.

Methods:
A prospective, randomized clinical trial was conducted on 60 patients undergoing laser-assisted laryngeal microsurgery for vocal cord tumours. All patients received an induction mivacurium dose of 0.2 mg kg^–1 and were randomized to 3 groups, namely C1, C2 and C3, each receiving infusion rates of 6 μg kg^–1 min^–1, 7 μg kg^–1 min^–1, 8 μg kg^–1 min^–1, respectively. Neuromuscular monitoring and pharmacodynamic para­meters of mivacurium were recorded.

Results:
No cases of airway spasms, blood pressure or heart rate fluctuations were observed. Three patients had skin redness at the injection site. The onset time, no- response time, and recovery index (RI) of mivacurium did not differ significantly among the groups. However, additional mivacurium doses were needed for 15 patients in C1, 10 patients in C2, and 3 patients in C3 (P < 0.05). In C1, 2 patients had vocal cord immobility at T1 = 0. An RI > 5.68 min was correlated with reduced mivacurium supplementation, and it was associated with no-response time and total mivacurium dose. The recovery index of all patients was also positively correlated with total mivacurium dosage (p < 0.0001, r = 0.7838).

Conclusions:
A mivacurium infusion rate of 8 μg kg^–1 min^–1 offered the most favourable surgical field condition with no involuntary vocal cord movements, less need for supplementary doses, and fewer adverse reactions in laser-assisted laryngeal microsurgery.