Effect of neuromuscular blockade on transcranial electric motor evoked potentials during surgical correction for idiopathic scoliosis under total intravenous anesthesia

Transcranial electric motor evoked potentials (TCeMEPs) play an important role in reducing the risk of iatrogenic paraplegia. TCeMEPs could be obviously suppressed by neuromuscular blockade (NMB). The aims of this study were to examine the effects of NMB on TCeMEPs and to determine an appropriate level of partial neuromuscular blockade (pNMB) for TCeMEPs during surgical correction of idiopathic scoliosis under total intravenous anesthesia (TIVA). All patients were maintained with TIVA. The pNMB levels were classified into five phases: one or two train-of-four (TOF) counts (TOF₁); three TOF counts, or T₄/T₁ (TOFR, T_1,4, first or four twitch height of TOF) ≤ 15% (TOF₂); TOFR at 16–25% (TOF₃); TOFR at 26–50% (TOF₄); and TOFR at 51–75% (TOF₅). No neuromuscular blockade (nNMB) was achieved when TOFR was more than 75%. The absolute and relative latency, amplitude and area under curve (AUC), efficacy of TCeMEPs and rate of unexpected movement were compared among these phases. Neither the amplitude and AUC nor the efficacy of TCeMEPs were affected at TOF₄₋₅ of abductor halluces muscles TCeMEPs (AH-TCeMEPs) or at TOF₃₋₅ of tibialis anterior muscles TCeMEPs (TA-TCeMEPs) compared with nNMB. However, the rate of unexpected movement was increased significantly at TOF₅ and nNMB compared with TOF₁ and TOF₄. The application of pNMB with TOFR aimed at 26–50% for AH-TCeMEPs or 16–50% for TA-TCeMEPs seems to be an appropriate regimen for TCeMEPs during surgical correction for idiopathic scoliosis under TIVA.