Evaluation of post-tetanic motor evoked potential as an augmentation technique under partial neuromuscular blockade during craniotomy

Objective: In craniotomies requiring motor evoked potential (MEP) monitoring, avoiding neuromuscular blockade (NMB) is preferable, but its complete avoidance poses risks of unexpected movement. This retrospective study investigates the application of a post-tetanic MEP augmentation technique to enhance baseline recording of transcranial stimulation MEP (Tc-MEP) under partial NMB during craniotomy.

Methods: Twenty-six patients were included. The level of partial NMB was maintained at a train-of-four ratio of approximately 40 %. Monophasic constant-current stimulation was applied on the craniotomy side with + 20 % of the threshold intensity. Post-tetanic Tc-MEP, involving tetanic stimulation of the median nerve 1 s before transcranial stimulation, was performed on patients who failed to record using conventional baseline recording.

Results: The post-tetanic Tc-MEP technique successfully improved the success rate of baseline recording from 61.5 % to 100 %. Application of post-tetanic Tc-MEP significantly increased amplitudes in both the upper (p = 0.04) and lower limbs (p < 0.01) compared to before post-tetanic Tc-MEP. No patients had unexpected movements.

Conclusions: This study indicates that post-tetanic Tc-MEP enhanced the success rate of baseline recording during craniotomy under partial NMB.

Significance: The combination of partial NMB and post-tetanic Tc-MEP could be a useful regimen for craniotomy with MEP monitoring, addressing both safety concerns and successful baseline recording.