Motor Evoked Potential Monitoring During Robot- Assisted Transaxillary Thyroid Surgery: A Report of Feasibility in Two Cases

Case Report

Austin J Biomed Eng. 2015; 2(1): 1031.

Motor Evoked Potential Monitoring During Robot- Assisted Transaxillary Thyroid Surgery: A Report of Feasibility in Two Cases

Gilles Boccara¹*, Helen Pickburn¹, Patrick Aidan¹, M Bernard Ollat² and M Pascal Pagneux²

¹Department of Anesthesia and Intensive Care, American Hospital of Paris, Neuilly S/Seine, France

²Biomedical Department of American Hospital of Paris, France

*Corresponding author: Gilles Boccara, Department of Anesthesia and Intensive Care, American Hospital of Paris, Neuilly S/Seine, France

Received: October 12, 2015; Accepted: December 30, 2015; Published: December 31, 2015

Abstract

Gasless Transaxillary robotic thyroid surgery has recently been proposed and developed in many countries. We report the feasibility of continuous intraoperative neuromonitoring of Transcranial Electric Motor Evoked Potentials (tceMEP) in two cases in order to monitor the risk of brachial plexopathy due to ipsilateral arm positioning during the axillary approach. The anesthetic implications are also described, specifically the use of intraoperative monitoring.

Keywords: Motor evoked potential; Anesthesia; Thyroid; Robot; Axillary

Introduction

The transaxillary robotic approach to thyroid surgery was first proposed in 2007 in Korea and has since been performed in North America [1-4]. During the initial experience at our clinical centre with this procedure one case of transient ipsilateral brachial plexopathy occurred [5].

The incidence of ipsilateral brachial plexopathy during the transaxillary robotic approach to thyroid surgery is assessed to be near to 0.3% [6], but if systematically searched for using neuromonitoring this figure would be likely be higher. There are two techniques currently proposed to prevent brachial plexopathy during the Transaxillary robotic approach. Firstly, owing to the constraints of surgical duration and the learning curve of this method the risk of plexopathy could be prevented by using the modified arm position as proposed by Kuppersmith et al. [7]. Secondarily, intraoperative multimodality neuromonitoring to aid the detection of evolving positional brachial plexus injuries could be utilized [8,9]. We report in two cases the feasibility of continuous intraoperative neuromonitoring of Transcranial Electric Motor Evoked Potentials (tceMEP) during the transaxillary robotic approach to thyroid surgery and the ensuing anesthetic implications.

Case Report

This report describes two patients who underwent thyroid lobectomy using the robotic axillary approach (da Vinci Si HD Surgical System, Intuitive Surgical, Sunnyvale, CA). The patients were enrolled and clearly informed about the advantages and risks of conventional open versus robot-assisted transaxillary thyroid surgery and gave preoperative written consent.

After oral premedication with hydroxyzine (1 mg.kg-1) and gabapentin (5 mg.kg-1) general anesthesia was initiated with a Target Controlled Infusion (TCI) of propofol and remifentanil. A single dose of intravenous atracurium (0.5 mg.kg-1) was used to facilitate endotracheal intubation. Endotracheal intubation was performed using a tube equipped with electrodes to allow for nerve stimulation and to aid in the detection of injury to the recurrent nerve by stimulated electromyography of the vocal cords (Xomed NIM II EMG endotracheal tube II, Medtronic Inc., Jacksonville, FL). Propofol and remifentanil administration using TCI were adjusted according to the depth of sedation, assessed by EEG bispectral analysis with an objective range 40 to 55 (BIS, Aspect Medical Systems, Newton, MA), and guided by blood pressure and heart rate monitoring. Mechanical ventilation on volume control with mixed oxygen/air was titrated an oxygen saturation (SpO2) > 97% and end-tidal carbon dioxide between 30 and 36 mmHg. A forced-air warming blanket was positioned before induction and used throughout the procedure.

According to the guidelines relating to remifentanil use, intravenous acetaminophen (1 g), ketoprofen (100 mg) and nefopam (20 mg) were infused 60 minutes prior to skin closure and TCI interruption to prevent post-operative analgesia. Upon waking, and after endotracheal extubation, intravenous morphine was titrated in the recovery room using the Visual Analog Scale (VAS) (a score greater than 3/10 indicating the need for opiate analgesia). Injury to the recurrent laryngeal nerve was assessed intraoperatively using nerve stimulation and post-operatively by the detection of voice changes.

During surgery the patients were positioned supine on the operating table with a soft triangular pillow under the shoulders and the contralateral upper limb alongside the body. Continuous intraoperative neuromonitoring of transcranial electric motor evoked potentials (tceMEP) was performed using the NIM-Eclipse (Medtronic, Medtronic Inc., Jacksonville, FL). To perform the tceMEP needle electrodes were placed in biceps, triceps, extensor carpi radialis and flexor carpi ulnaris. Electrical stimulation with brief, high-voltage (300–1,000 V) anodal pulse trains (pulse width ¼ 50 ls, N pulses ¼ 3–7, interpulse interval ¼ 1–5) was induced. The stimulus was delivered between two subdermal needle electrodes inserted subcutaneously over motor cortex regions C1 and C2. In order to check the effective response and disappearance of muscle relaxation the extensor carpi radialis in the contralateral arm was also monitored. The ipsilateral upper limb was placed in the modified position suggested by Kuppersmith et al. [10], with right angle flexion of the elbow and the forearm positioned before the head (Figure 1) so the axillary space could be freely accessed [5,11]. Stimulation was performed at the following times: in neutral arm position, in modified arm position before incision, during dissection of the working space, after retractor placement, during robotic working time (Figure 2), after removal of robotic instruments, after skin closure and after infiltration by 10-15 ml of 0.75% ropivacaine and placement of the ipsilateral arm alongside the body.