Threshold-guided optimization of transcranial electrical stimulation parameters for motor evoked potential monitoring in pediatric spinal surgery

Transcranial electrical stimulation motor evoked potential (TES-MEP) monitoring during pediatric spinal surgery is technically challenging due to developmental corticospinal physiology. We quantified the effects of electrode montage, stimulation pattern, and interstimulus interval (ISI) on motor threshold (MT) to define a practical optimization protocol for pediatric neuromonitoring. Eighty-one pediatric patients (0.5–17 years) undergoing spinal or spinal cord surgery were analyzed using a prospective within-patient design. Effects of montage and stimulation pattern were assessed with repeated-measures ANOVA. ISI modulation (2, 3, 4 ms) was evaluated within the linked quadripolar montage with double-train stimulation (LQP-DTS) in patients without floor effect ( n = 65). Multivariable regression identified determinants of baseline MT, ISI responsiveness, and pulse escalation. Montage and stimulation pattern exerted large independent effects on MT ( η 2 p = 0.986 and 0.969; both p < 0.001). LQP-DTS reduced mean MT by 77.8 V (95% CI 76.1–79.6) compared with C1–C2 STS and produced the lowest threshold in all patients. ISI significantly modulated MT ( η 2 p = 0.868, p < 0.001), with a 17.35 V increase at 2 ms and a 3.46 V decrease at 4 ms relative to 3 ms. Younger age and preoperative motor deficit independently predicted higher baseline MT ( R 2 = 0.699, p < 0.001). Baseline MT predicted ISI responsiveness and pulse escalation (AUC 0.917–0.918). Pediatric TES-MEP thresholds follow a reproducible physiological hierarchy. Optimization using LQP-DTS at ISI 3 ms with threshold-guided adjustment reduces stimulation requirements and supports reliable corticospinal monitoring during pediatric spinal surgery.