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CASE REPORT Table of Contents  
Ahead of print publication
Boxer's mouthguard to facilitate motor evoked potential monitoring during cervical intramedullary tumour excision: Protect and prevent rather than repair and repent!

 Department of Anaesthesiology, Division of Neuroanesthesia, P. D. Hinduja Hospital and Medical Research Centre, Mumbai, Maharashtra, India

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Date of Submission15-Aug-2022
Date of Acceptance15-Oct-2022
Date of Web Publication07-Nov-2022


Intraoperative motor evoked potentials are being increasingly used in surgeries for the removal of spinal tumours. However, this useful monitoring is accompanied by risks such as bite injury to the tongue and oral mucosal soft tissues due to clenching of the teeth and jaws as the patient may not be completely under the effect of neuromuscular blocking agents, resulting in bleeding in the oropharynx. To prevent these complications, we conceptualised and utilised a boxer's mouthguard as a preventive protection during cervical intramedullary tumour excision surgery. Such mouthguards are routinely used in contact sports such as boxing but their clinical application in neuroanaesthesia has not been described. This use is a novel, economical, convenient, standardised and easy way of bite protection and preventing intraoperative tongue, soft-tissue injuries and airway complications.

Keywords: Boxer's mouthguard, motor evoked potential monitoring, neuroanaesthesia, spine

How to cite this URL:
Bedekar UP, Monteiro JN. Boxer's mouthguard to facilitate motor evoked potential monitoring during cervical intramedullary tumour excision: Protect and prevent rather than repair and repent!. Airway [Epub ahead of print] [cited 2022 Nov 28]. Available from: https://www.arwy.org/preprintarticle.asp?id=360524

  Introduction Top

Intraoperative neuromonitoring with partial or no neuromuscular blocking agents is accompanied by risks such as bite injury to the tongue and oral mucosal soft tissues. We conceptualised and utilised a boxer's mouthguard as a preventive protection. Such mouthguards are routinely used in contact sports such as boxing but their clinical application in neuroanesthesia has not been previously described.

  Case Report Top

Intraoperative neuromonitoring with motor evoked potentials (MEPs) is used in spine surgeries. This leads to a variety of potential complications such as tongue injury, oral mucosal bleeding and airway oedema. Various protective strategies are being implemented to prevent these iatrogenic complications. A novel way to overcome this problem is being described in our case by the use of a boxer's mouthguard.

A 46-year-old woman with complaints of left shoulder pain, tingling and numbness for the past 8 months and left thigh, ankle and foot tingling for the past 4 months was diagnosed to have a lesion at the level of C6-C7 spine. She complained of difficulty in getting up from the squatting position and wearing slippers. She also complained of urinary incontinence for the past 20 days. There were no other comorbidities or known allergies. Except for the presence of buck teeth, her airway examination was normal. Muscle power was 4/5 in both the lower limbs. There was hypertonia in the lower limbs with exaggerated reflexes and plantar flexors. Routine haematological and serological investigations were normal. Magnetic resonance imaging revealed a hyperintense lesion 13 mm × 13 mm × 17 mm size at the level of C6-C7.

After obtaining written informed consent, checking the nil per oral status and performing the preoperative WHO surgical checklist, preinduction monitors including electrocardiogram, noninvasive blood pressure, pulse oximetry, neuromuscular transmission and bispectral index (BIS) were established.

A boxer's mouthguard [Figure 1] was placed in lukewarm water in operation theatre and it was applied to the upper teeth after induction of the patient [Figure 2]. General anaesthesia was administered with intravenous midazolam (0.02 mg/kg), fentanyl (2 μg/kg), propofol (1 mg/kg) and atracurium besylate (0.5 mg/kg). The patient was intubated with a 7.0 mm ID flexometallic armoured endotracheal tube and the airway was secured [Figure 2]. Anaesthesia was maintained with a 50:50 mixture of air:oxygen and intravenous titrated infusions of propofol and dexmedetomidine. Adequate analgesia was ensured with titrated aliquots of fentanyl. Postinduction monitors included invasive arterial blood pressure, somatosensory evoked potentials (SSEPs) and MEPs, following which the patient was carefully proned in a synchronised coordinated manner. To prevent tongue protrusion in the prone position, an additional bite block in the form of folded gauze pieces may be of help.
Figure 1: Boxer's mouthguard

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Figure 2: The patient with the mouthguard placed preinduction (a) and after anaesthesia with endotracheal tube in situ (b)

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The position of the endotracheal tube and bilateral air entry was confirmed and pressure points were padded meticulously. A baseline recording of MEP and SSEP was done. Intraoperative depth of anaesthesia was monitored and BIS was maintained between 40 and 60 and train-of-four monitoring maintained at more than two twitches.

The procedure was uneventful. During the course of tumour removal and after the removal, MEP recordings were documented. During stimulation, the mouthguard prevented damage to teeth, oral soft tissues and tongue and subsequent airway compromise. The mouthguard was removed from the mouth after making the patient supine just prior to extubation. The teeth of the patient were intact postoperatively. The patient was extubated after fulfilling the requisite extubation criteria.

  Discussion Top

Complications such as tongue bite, bleeding into the oropharynx and injury to the oral mucosa are common in cases where MEPs are used for monitoring. The corticospinal tract is stimulated by the firing of motor electrode and the distal muscle functions are checked. This may lead to injury to the lips and tongue. Tongue injuries occurred approximately four times as frequently as injuries of the lip.[1] Tongue injury occurs because of jaw clenching or muscle or trigeminal nerve stimulation during the surgery.[2] In addition, in the prone position, the risk of tongue injury is aggravated due to gravity-induced protrusion and obstruction to venous return subsequently causing oedema.[3] This may lead to delayed extubation and endotracheal tube damage.

Bite blocks have been traditionally used to secure the tongue, but they do fail sometimes due to dislodgement and movement of the tongue between the teeth. The bite block should ideally secure the front and molar teeth and keep the tongue in the centre.[4] Hard bite blocks are not recommended as they increase the chances of tongue lacerations. There is no consensus on what constitutes an ideal bite block.

We conceptualised and used a soft but firm mouthguard normally employed by professional boxers. It was a form of 'boil and bite mouthguard' made up of thermoelastic material which adapts to the mouth after immersing in lukewarm water. The mouthguard is meant to act as a buffer by moving the soft tissues in the oral cavity away from the teeth preventing lacerations and bruising of lips, cheeks and tongue during an impact.[5] It was introduced after anaesthesia was induced and before attempting laryngoscopy for endotracheal intubation. It is reported in the literature that there is an altered mandibular position on lateral skull radiographs, so that the condyles are distracted from their fossae after the application of mouthguards.[5]

The use of boxer's mouthguard also prevented the damage to the protruding upper front teeth from the horizontal flange of the direct laryngoscope which rested on them during intubation. This made the process of intubation trauma-free and safe.

  Conclusion Top

The use of a boxer's mouthguard is an innovative, convenient and simple way to protect the airway while recording MEPs in spine surgeries with the skull being fixed on the head frame. The use of such a simple, standardised device for the safety of the patient and to prevent any iatrogenic complications is advisable. Although the use of a mouthguard has been described in the postoperative period to save the tongue from injury produced by seizures, its intraoperative use for airway protection during neuromonitoring in spine surgery is novel.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Tamkus A, Rice K. The incidence of bite injuries associated with transcranial motor-evoked potential monitoring. Anesth Analg 2012;115:663-7.  Back to cited text no. 1
Williams A, Singh G. Tongue bite injury after use of transcranial electric stimulation motor-evoked potential monitoring. J Anaesthesiol Clin Pharmacol 2014;30:439-40.  Back to cited text no. 2
[PUBMED]  [Full text]  
Chae YJ, Kim JY, Yoo JY, Choi YH, Park KS. Tongue bite in a patient with tracheostomy after prone position – A case report. Korean J Anesthesiol 2011;60:365-8.  Back to cited text no. 3
Pisklakov S, Le V, Sandoval P. Tongue laceration during neurophysiologic monitoring with motor evoked potentials. Open J Anesthesiol 2012;2:226-7.  Back to cited text no. 4
Mantri SS, Mantri SP, Deogade S, Bhasin AS. Intra-oral mouth-guard in sport related oro-facial injuries: Prevention is better than cure! J Clin Diagn Res 2014;8:299-302.  Back to cited text no. 5

Correspondence Address:
Joseph Nascimento Monteiro,
Department of Anaesthesiology, Division of Neuroanesthesia, P. D. Hinduja Hospital and Medical Research Centre, Veer Savarkar Road, Mahim, Mumbai - 400 016, Maharashtra
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Source of Support: None, Conflict of Interest: None


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