Mivacurium Infusion ED50/ED95 for Maintaining Motor Evoked Potentials During Adolescent Scoliosis Surgery Under TIVA:...

This study aimed to determine the median effective dose (ED50) and 95% effective dose (ED95) of mivacurium for maintaining elicitable motor evoked potentials (MEP) under total intravenous anesthesia (TIVA) during adolescent scoliosis surgery, while fulfilling both muscle relaxation and intraoperative neurophysiological monitoring (IONM) requirements.

26 adolescents scheduled for primary elective scoliosis surgery with MEP monitoring were enrolled. Anesthesia was maintained with TCI propofol to achieve BIS of 40-60. Infusing mivacurium to maintain train-of-four count 1-3 until surgical exposure was completed. After train-of-four ratio recovered to 75% and MEP waveforms were elicitable, modified Dixon up-and-down sequential method was employed, with an initial mivacurium infusion dose of 10 μg·kg^-1·min^-1, adjusted by 0.5 μg·kg^-1·min^-1 based on the presence or absence of reproducible MEP at predefined stimulation settings. Positive was defined as reproducible MEP waveform elicitable at a stimulus intensity of 100 V. Dose-finding proceeded until seven crossover pairs were obtained. Excluding cases prior to the first crossover, 21 patients contributed to ED estimation. Hemodynamic parameters, adverse reactions, vasoactive agents use, and L-SRS scores were recorded.

The ED50 was 7.24 μg·kg^-1·min^-1 (95% CI: 6.87-7.54). The probability of MEP waveform presence demonstrated a negative correlation with mivacurium infusion dose, with an ED95 of 6.70 μg·kg^-1·min^-1 (95% CI: 4.79-6.99). No patients experienced unintended body movements, spontaneous respiration recovery, or bronchospasm. No significant hemodynamic changes were observed after mivacurium administration. Transient skin flushing occurred in 6 patients, and low-dose ephedrine was required in 7 patients. L-SRS scores were higher during mivacurium infusion compared to post-discontinuation.

Under this TIVA/IONM protocol, the ED50 and ED95 for continuous mivacurium infusion that preserves MEP are 7.24 μg·kg^-1·min^-1 and 6.70 μg·kg^-1·min^-1, respectively. These doses effectively achieve muscle relaxation while maintaining MEP signals without serious adverse events observed.