Lingual nerve injury is a rare complication of airway manipulation during anaesthesia. Virtually all devices used for airway instrumentation and manipulation have been previously implicated in its cause. The cuffed oropharyngeal airway (COPA) is a modified Guedel airway first described by Greenberg in 1990  and is recommended for anaesthesia in spontaneously breathing patients. We are unaware of any reports of lingual nerve damage after the use of a cuffed oropharyngeal airway.
A healthy 29-year-old woman weighing 60kg presented for elective arthroscopy of her right ankle. She smoked 10 cigarettes a day and had no known allergies. Examination of the airway revealed a Mallampati class I airway with normal mouth opening and slightly receding mandible. Anaesthesia was induced with fentanyl 75μg and propofol 200mg. A size 10 COPA was inserted at the second attempt using a technique previously described . Jaw thrust was applied during insertion and the cuff was inflated with 40 mL of air to obtain a clear airway with an airtight seal. Anaesthesia was maintained using a mixture of nitrous oxide, oxygen and isoflurane. The procedure proceeded uneventfully, with no significant changes in cardiovascular or respiratory parameters. No airway manipulation was required to maintain an unobstructed airway. The time from the start of anaesthetic to the end of surgery was 65min. The patient was transferred to the recovery area breathing oxygen via a Hudson mask with the COPA in situ and its cuff already deflated. A recovery nurse removed the cuffed oropharyngeal airway when the patient's reflexes returned and the patient opened her mouth to command.
The patient complained of numbness on the left side of her tongue in the immediate postoperative period. On examination, there was complete loss of sensation to touch over the left antero-lateral region of her tongue with associated loss of taste discrimination. There was no motor deficit, swelling, oedema or bleeding in the oral cavity. The patient was reassured, explained the possible causes of her symptoms and asked to contact us if these worsened. She was discharged home on the same day. Telephone follow-up revealed that the symptoms on the left side of her tongue resolved spontaneously after 10 days.
It is surprising that injury to the lingual nerve is a rare occurrence considering the degree of the manipulation required in the oral cavity for safe airway management.
Virtually all the equipment associated with airway management has previously been implicated in its damage. Examples of these include direct laryngoscopy , tracheal intubation [4,5] and the laryngeal mask airway [6, 7, 8]. Some manipulations associated with the airway, such as jaw thrust and application of cricoid pressure, have also been implicated. The cuffed oropharyngeal airway is a modified Guedel airway used for anaesthesia in spontaneously breathing patients. To our knowledge lingual nerve palsy associated with use of this device has not been previously reported.
The aetiology of lingual nerve damage appears to be multifactorial: anatomical and technical factors, in addition to the compression of the nerve, may be involved. Forceful laryngoscopy with tongue compression, a resultant swelling at the base of the tongue, cricoid pressure and anterior displacement of the mandible have all been implicated [2,3,8, 9, 10, 11].
In order to understand the mechanisms involved in its damage, it is important to trace the course of the lingual nerve and understand its anatomy in relation to the structures in the oral cavity where it may be liable to damage. The lingual nerve supplies the sensation to the mucous membrane of the presulcal part of the tongue. It is a branch of the posterior trunk of the mandibular nerve. It travels between the lateral pterygoid and tensor palati muscles, where it is joined by the chorda tympani which contains the afferent fibres from the taste buds in the presulcal area of the tongue. The nerve then descends between the medial and lateral pterygoid muscles and emerges from the cover of the lateral pterygoid to pass between the mandible and medial pterygoid. Here it may be prone to damage from anterior displacement of the mandible  as in the jaw thrust manoeuvre. It then passes below the mandibular origin of the superior constrictor and lies against the deep surface of the mandible just medial to the roots of the third lower molar immediately under the mucosa of the gum. At this site it may be liable to damage from forceful laryngoscopy [9,10]. The nerve then crosses to the side of the tongue over the styloglossus, running forwards on the lateral surface of the hyoglossus and genioglossus. The lingual nerve may become stretched as it crosses the hyoglossus during cricoid pressure, because the hyoid bone is prevented from moving forward with the tongue during laryngoscopy . Direct compression of the nerve along the superficial parts of its course has been reported . It then divides into its terminal branches that lie deep to the mucous membrane of the tongue .
It is difficult to postulate one mechanism for the lingual nerve injury in our case. The cuffed oropharyngeal airway, when properly inserted, lies along the length of the tongue and its distal tip is positioned just above the epiglottis. The inflated cuff is broad and flattened on the convex palatal side of the airway and small on the concave lingual side thus creating a tight seal by forming a plug in the upper pharynx . It is possible that the cuff may have caused compression of the nerve against the mandible, or stretched the nerve over the hyoglossus. Cuff volume is an important factor in determining the correct position of the COPA and it is possible that the pressure in the cuff could have increased as a result of nitrous oxide. There may be a risk of increased cuff pressure when nitrous oxide is used because it diffuses into the cuff faster than oxygen or nitrogen diffuse out as has been shown with the laryngeal mask airway . The volume of air used to inflate the cuff was 40 mL, which is within the range used in earlier studies . Airway manipulation in the form of jaw thrust was only required during insertion of the cuffed oropharyngeal airway and it was not excessive.
Whatever the cause of the lingual nerve injury, it is important to establish the diagnosis and manage the case by regular follow-up and provide support and reassurance to the patient.
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