An evaluation of anesthetic fade in motor evoked potential monitoring in spinal deformity surgeries

Abstract

BackgroundIntraoperative neuromonitoring using motor evoked potentials (MEP) satisfactorily detects motor tract integrity changes during spinal surgery. However, monitoring is affected by “anesthetic fade,” in which the stimulation threshold increases because the waveform amplitude decreases with the accumulation of propofol. Therefore, the purpose of this study was to clarify the effect of anesthetic fade on transcranial MEPs by investigating the time-dependent changes of amplitude during spinal deformity surgeries.MethodsWe retrospectively reviewed medical records of 142 spinal deformity patients (66 patients with idiopathic scoliosis, 28 with adult spinal deformities, 19 with neuromuscular scoliosis, 17 with syndromic scoliosis, and 12 with congenital scoliosis). The average age was 28 years (range, 5 to 81 years). MEPs were recorded bilaterally from the abductor digiti minimi (ADM) and abductor hallucis (AH) muscles during spinal deformity surgeries. The Wilcoxon signed-rank test was used to investigate the time-dependent changes of amplitude after propofol infusion to evaluate anesthetic fade effects.ResultsThe average time to baseline from initial propofol infusion was 113 min (range, 45 to 182 min). In the ADM, the amplitude was 52% at 1 h after initial propofol infusion, 102% at 2 h, 105% at 3 h, 101% at 4 h, 86% at 5 h, and 81% at 6 h. Compared to the 2-h time point, MEP decreased significantly by 16% at 5 h (P < 0.0005) and by 21% at 6 h (P < 0.05). In the AH, the amplitude was 49% at 1 h after initial infusion of propofol, 102% at 2 h, 102% at 3 h, 92% at 4 h, 71% at 5 h, and 63% at 6 h. Compared to the 2-h time point, MEP decreased significantly by 10% at 4 h (P < 0.005), by 31% at 5 h (P < 0.0000005), and by 39% at 6 h (P < 0.05).ConclusionsMEP amplitude significantly decreased in the upper limbs at 5 and 6 h and in the lower limbs at 4, 5, and 6 h after the initial infusion of propofol, respectively. The influence of anesthetic fade could influence false positive MEPs during long spinal surgeries.

The influence of anesthesia on intraoperative neurophysiological monitoring during spinal surgeries

“…Reports suggest that tc-MEP responses degrade or undergo anesthetic fade during surgery despite unchanged anesthetic levels and other physiologic variables (5). In a study by Ugawa et al (41), the amplitude of MEP signifi cantly decreased in the lower limbs at 5 hours by 31 % and at 6 hours by 39 % after the initial infusion of propofol. Mean operating time was 282.1 minutes.…”

Amplitude-reduction alert criteria and intervention during complex paediatric cervical spine surgery

“…Alerts were more frequently identified in the MEP modality, perhaps due to increased sensitivity in detecting spinal cord ischaemia when compared to SSEPs ( Shils and Deletis, 2020 ). However, inter- and intra-individual variability of muscle MEPs under prolonged general anaesthesia can make amplitude-reduction criteria vulnerable to false reporting ( Ugawa et al, 2018 ). Eighty percent reduction alert criteria used in spinal surgery have 91–100 % sensitivity, 91–100 % specificity; a 61–100 % positive predictive value, and a 76–100 % negative predictive value ( Journée et al, 2017 ).…”

Can Evoked Potential Changes during the Superficial Temporal Artery-Middle Cerebral Artery Bypass Surgery Predict Postoperative Improvement of Cerebral Perfusion and Functional Status?

“…This may affect the final EP and can underestimate the increase in MEP amplitude reflecting blood flow improvement [ 38 ]. Ugawa et al [ 39 ] studied anesthetic fade effects on MEP in spinal deformity surgeries. Their results revealed a significant decrease in MEP amplitude (16%) in the upper extremity 5 h after the initial propofol infusion and a significant decrease in MEP amplitude (10%) in the lower extremity 4 h after the initial propofol infusion.…”