Bilateral lingual nerve injury associated with classic laryngeal mask airway

Abstract

Editor, A 36-year-old American Society of Anesthesiologists physical status Class I woman underwent a myomectomy for uterine fibroid. A size 4 classic laryngeal mask airway (LMA) was easily and atraumatically inserted and cuff inflated. Positive pressure ventilation started with no detectable air leak. Anaesthesia was maintained with sevoflurane 2–3% in O2/air. Procedure was prolonged due to surgical difficulties and intraoperative bleeding to a total time of 180 min. In recovery, patient reported tongue numbness and abnormal taste sensation over the anterior two thirds of the tongue. No obvious swelling, haematoma or bleeding in the oral cavity was noticed. After 3 weeks, she felt that 90% of the tongue sensation had returned to normal. It took 6 weeks for complete resolution of her symptoms; a diagnosis of lingual nerve damage was made based on the clinical presentation and relevant clinical examination. Patient consent was obtained for publication of this case report. Lingual nerve is a branch of the third division of the trigeminal nerve; it carries taste fibres from the facial nerve, namely the chorda tympani, supplying the anterior two thirds of the tongue. During its course, it lies in close proximity to the mandible, making it vulnerable to compression and damage. Injury could present with varying symptoms of neuropathic pain.1 Several reports of cranial nerve damage (lingual, hypoglossal and recurrent laryngeal nerve)2 as well as submandibular and parotid gland swellings3 have been published. The majority are related to the classic LMA, a few are related to ProSeal LMA. The mechanism of injury to the lingual nerve has been described before as a pressure neuropraxia when it enters the oral cavity below the inferior border of the superior constrictor muscle. Potential predisposing factors include traumatic insertion, high cuff pressures, use of small-size LMA, use of nitrous oxide, malpositioning including lateral position and extreme head-side rotation. Small-size LMA and the use of nitrous oxide were a common factor in most of the cases. Nitrous oxide diffuses into the cuff, leading to an increase in its pressure. This is likely to build up with time. Anaesthetists should be vigilant in monitoring cuff pressures during the procedure if nitrous oxide to be used. The classic LMA should be inflated according to manufacturer's guidelines using a volume-controlled technique aiming to achieve an adequate seal and avoiding intracuff pressure above 60 cmH2O. In this case, the only indeterminate was cuff pressure. If a manometer is not readily available, the use of a 10-ml syringe connected to the pilot balloon and allowed to equilibrate could give a good estimate of correct cuff pressure.4 To avoid nerve damage, the following conditions must be considered: Use the appropriate size LMA for the case, 4 for women and 5 for men. Gentle airway manipulation. Avoid cuff pressure above 60 cmH2O. Ensure cuff pressure measurement every 30 min, if using nitrous oxide. Avoid extreme neck positions. Have a low threshold of suspicion for lingual nerve damage if patient reports abnormal sensation/taste. What to do if it happens: Early referral to a specialist is required. Tests for light touch, pin prick and two-point discrimination could be used to identify the baseline and monitor progress. Clear documentation of patient complaints and clinical findings helped with schematic illustration to the areas of damage for further assessment and follow-up. If problems of neuropathic pain are encountered, a referral to a pain specialist might be required. In summary, cranial nerve damage related to the use of supraglottic airway devices is a rare but well described occurrence. Despite avoiding all known risk factors damage may still occur. We cannot overemphasis the need for cuff pressure measurement by some validated means. Close monitoring for improvement is vital, as without signs of improvement early intervention is essential. Acknowledgements The authors would like to declare that they have not received any assistance, financial support or sponsorship in relation to above publication and have no conflicts of interest.