Effects of rocuronium dosage on intraoperative neurophysiological monitoring in patients undergoing spinal surgery

Intraoperative neurophysiological monitoring (IONM) has been widely used in clinical practice. Therefore, the influence of neuromuscular blockers essential for spinal anaesthesia on IONM is worthy of our attention, but no randomized study has evaluated the dose-response effect. This study investigated the effects of different doses of rocuronium bromide on the intraoperative monitoring of motor evoked potentials (MEPs).

We conducted a randomized, double-blind trial to assess the effects of three rocuronium bromide doses (6.0, 9.0, 12 μg·kg^-1 ·min^-1 ) combined with intravenous infusion of propofol 6-8 mg·kg^-1 ·h^-1 and remifentanil 10 μg·kg^-1 ·h^-1 on the amplitudes of somatosensory evoked potentials (SEPs) and MEPs at the time of the baseline recording (T₁ ), before pedicle screw placement (T₂ ) and before spinal canal decompression (T₃ ). Secondary outcomes included measurement of neuromuscular function, the occurrence of unexpected intraoperative body movement and recovery of spontaneous breathing.

A total of 123 patients were enrolled, and 120 patients were ultimately analysed. No differences were observed in the amplitude of SEPs among the three groups (p > 0.05). The MEP amplitude differences at T₁ , T₂ and T₃ in all limbs did not differ in patients receiving rocuronium at 6.0 μg·kg^-1 ·min^-1 and 9.0 μg·kg^-1 ·min^-1 (p > 0.05). However, when rocuronium was administered at 12.0 μg·kg^-1 ·min^-1 , MEP amplitudes at the time point T₃ were significantly attenuated compared with the time points T₁ and T₂ in both right upper limb and left lower limb (p = 0.002, p = 0.025, respectively). In patients treated with rocuronium 6.0 μg·kg^-1 ·min^-1 , the incidence of unexpected body movement was significantly higher (p = 0.026), and the train-of-four count (TOF count) showed a significant increase at T₂ and T₃ (p < 0.001) compared to other doses.

Rocuronium bromide at a rate of 9.0 μg·kg^-1 ·min^-1 provided suitable and adequate muscle relaxation without inhibiting IONM; thus, this dose is recommended for spinal surgery.