Effect of dexmedetomidine on somatosensory- and motor-evoked potentials in patients receiving craniotomy under propofol-sevoflurane combined anesthesia

Abstract

Introduction: Dexmedetomidine is often used as an adjunct to total intravenous anesthesia (TIVA) for procedures requiring intraoperative neurophysiologic monitoring (IONM). However, it has been reported that dexmedetomidine might mask the warning of a neurological deficit on intraoperative monitoring.

Methods: We reviewed the intraoperative neurophysiological monitoring data of 47 patients who underwent surgery and IONM from March 2019 to March 2021 at the Department of Neurosurgery, Renmin Hospital of Wuhan University. Pre- and postoperative motor function scores were recorded and analyzed. Dexmedetomidine was administered intravenously at 0.5 μg/kg/h 40 min after anesthesia and discontinued after 1 h in the dexmedetomidine group.

Results: We found that the amplitude of transcranial motor-evoked potentials (Tce-MEPs) was significantly lower in the dexmedetomidine group than in the negative control group (P < 0.0001). There was no statistically significant difference in the somatosensory-evoked potentials (SSEPs) amplitude or the Tce-MEPs or SSEPs latency. There was no significant decrease in postoperative motor function in the dexmedetomidine group compared with the preoperative group, suggesting that there is no evidence that dexmedetomidine affects patient prognosis. In addition, we noticed a synchronized bilateral decrease in the Tce-MEPs amplitude in the dexmedetomidine group and a mostly unilateral decrease on the side of the brain injury in the positive control group (P = 0.001).

Discussion: Although dexmedetomidine does not affect the prognosis of patients undergoing craniotomy, the potential risks and benefits of applying it as an adjunctive medication during craniotomy should be carefully evaluated. When dexmedetomidine is administered, Tce-MEPs should be monitored. When a decrease in the Tce-MEPs amplitude is detected, the cause of the decrease in the MEPs amplitude can be indirectly determined by whether the decrease is bilateral.

Keywords: dexmedetomidine; intraoperative neurophysiological monitoring; neurosurgery; prognosis; transcranial motor-evoked potentials.

Figure 1

Flowchart of the patient selection and grouping. We screened 47 patients who met the inclusion criteria from 87 patients in total and categorized them into four groups according to whether dexmedetomidine was applied intraoperatively, whether there was a decrease in the amplitude of Tce-MEPs, and whether there were postoperative motor deficits. DEX means dexmedetomidine.

Figure 2

Flow chart of the study protocol. Dexmedetomidine was infused intravenously at 0.5 μg/kg/h 40 min after anesthesia and discontinued after 1 h in the dexmedetomidine group. Propofol-sevoflurane combined anesthesia was used in all the groups. Intraoperative vital signs were collected and recorded by the study coordinator at T0 and T1.

Figure 3

Diagram of intraoperative Tce-MEPs monitoring. During intraoperative monitoring of the Tce-MEPs amplitude on the left side of the patient, the polarity was switched by software, and positive and negative pulses were delivered through electrodes placed at C4 and C3, respectively. The amplitudes of the left upper Tce-MEPs (LUMEPs) and left lower Tce-MEPs (LLMEPs) were recorded by active electrodes placed over the belly of the contralateral thenar and abductor hallucis muscles.

Figure 4

Typical images of Tce-MEPs amplitudes over time in the 4 groups. (A) is an image of a 57-year-old woman with a right temporal lobe glioblastoma undergoing resection of a brain lesion with a −30%∼27% decrease in the percentage of the Tce-MEPs amplitude, and the patient's pre- and postoperative muscle strength assessments were both grade V. (B) is an image of a 51-year-old woman with a diffuse astrocytoma undergoing occipital lobe lesion excision with a 30%∼86% decrease in the percentage of the Tce-MEPs amplitude; the patient suffered no motor deficits after surgery. It is clear that the decrease in the Tce-MEPs amplitude occurred approximately 37 min after the infusion of dexmedetomidine, and the Tce-MEPs amplitude continued to decrease until 20 min after the dexmedetomidine infusion was stopped. (C) is an image of a 47-year-old woman with an intracranial aneurysm who underwent intracranial aneurysm clamping. The percentage of the Tce-MEPs amplitude decreased by 88%∼100% on the right side, while there was no decrease on the left side. The patient developed right hemiparesis after the operation. (D) and (E) are images of a 52-year-old woman with a cerebrovascular malformation undergoing resection of a skull base lesion and a 56-year-old man with a cavernous sinus-occupying lesion undergoing resection of a cavernous sinus lesion, respectively. Neither of the two patients had motor deficits postoperatively, although a decrease in the Tce-MEPs amplitude was observed in both patients. (F). Time course of RUMEP amplitude variability in the four groups.

Figure 5

Histograms of the intraoperative neurophysiological monitoring parameters in the four groups. (A) The percentage of amplitude decrease in Tce-MEPs. Dexmedetomidine vs. negative control: LUMEP 0.71 ± 0.19 vs. −0.15 ± 0.46, P < 0.0001; RUMEP 0.67 ± 0.26 vs. −0.001 ± 0.18, P < 0.0001; RLMEP 0.83 ± 0.15 vs. −0.26 ± 0.44, P = 0.012; LLMEP 0.73 ± 0.21 vs. −0.18 ± 0.44, P < 0.0001. (B) The percentage of latency growth in Tce-MEPs. No statistically significant difference was found. (C) The percentage of amplitude decrease in SSEPs. No statistically significant difference was found. (D) The percentage of latency growth in SSEPs. No statistically significant difference was found. (E) The absolute value of differences in the percentage of amplitude decreases in bilateral Tce-MEPs. Dexmedetomidine vs. positive control: 0.18 ± 0.17 vs. 2.9 ± 3.8, P = 0.001; Dexmedetomidine vs. fluctuating group: 0.18 ± 0.17 vs. 8.57 ± 17.4, P = 0.003; Negative control vs. positive control: 0.36 ± 0.35 vs. 2.9 ± 3.8, P = 0.009.