Unilateral hypoglossal nerve injury following the use of a ProSeal™ laryngeal mask

Abstract

We would like to report a complication following the use of a ProSeal™ laryngeal mask airway (PLMA) (Intavent Orthofix Ltd, Maidenhead, UK). A 28-year-old male required open reduction and internal fixation of a comminuted tibial plateau fracture. General anaesthesia was induced with infusions of propofol and remifentanil and his airway secured with a size 5 PLMA. The laryngeal mask was inflated with 40 ml of air. Anaesthesia was maintained with propofol, remifentanil, and nitrous oxide 70% in oxygen. Anaesthesia and surgery (which lasted 3.5 h) were uneventful. The PLMA was removed as the patient woke and was noted to be apparently overinflated. There were no immediate postoperative complications. The following day the patient complained of difficulty in swallowing and numbness on the left side of his tongue, present since shortly after waking up. Examination confirmed unilateral hypoglossal nerve injury. Throughout the rest of his time in hospital eating remained difficult. Full recovery of his hypoglossal nerve function was slow but complete at 4 months. Hypoglossal nerve, lingual nerve and recurrent laryngeal nerve injury have previously been reported during use of the classic laryngeal mask [1–4]. In most cases a full recovery was made. In one case hypoglossal nerve injury was accompanied by severe weight loss [1] and in another unilateral recurrent laryngeal nerve injury lead to permanent vocal cord paralysis [4]. The mechanism of injury is neuropraxia, due to pressure on the pharynx from the airway. In the case of the hypoglossal nerve this occurs at the medial side of the hyoid bone as the nerve crosses the greater cornu [5]. This is the first report of nerve injury associated with the PLMA. The PLMA has a larger cuff than the classic laryngeal mask airway and has a posterior extension. As a result the mask makes a larger area of contact with the pharynx and exerts lower pharyngeal pressures for the same intracuff volume [6]. The PLMA allows a better airway seal than the classic laryngeal mask airway for any given intracuff volume [6]. The rise in PLMA-airway seal is greatest for the first 10 ml of inflation, across the size range [6]. This, and other data suggest, that the PLMA is the least likely of the laryngeal masks to cause complications associated with increased pressure on pharyngeal mucosa, with the classic also better than the intubating laryngeal mask [7]. The 40 ml of air inserted into this PLMA represents the maximum volume that should be inserted into a size 5 PLMA. It is likely that the use of nitrous oxide and the long duration of surgery [8] both contributed to increased intracuff pressure, increased pharyngeal mucosal pressure and therefore neuropraxia. Audit elsewhere has shown that use of the maximum recommended volumes of air in all laryngeal masks routinely leads to intracuff pressures in excess of 120 cmH2O [9] and our own local audit has confirmed this. The practice of reducing the volume of air in the cuffs of laryngeal mask airways to half the recommended maximum has been shown not to interfere with mask function [10]. Brain has recommended both for the classic laryngeal mask airway and the PLMA that the maximum intracuff pressure should not exceed 60 cmH2O [11,12] and this information is contained in the instruction manuals of both devices [13,14]. At an intracuff pressure of 60 cmH2O, the pressure exerted on all areas of the mucosa by the PLMA is below that considered critical for mucosal perfusion [6]. Following this case, we have altered the practice in our hospital in order to try to prevent recurrence of this and similar complications. We have introduced cuff inflator/pressure gauges (VBM Mediztechnic, Sulz, Germany) to all areas where laryngeal mask airways are used allowing inflation to pressure of 60 cmH2O, and to enable monitoring of that pressure throughout anaesthesia. It appears that without use of such monitoring it is not possible to use the devices as recommended by the manufacturers. Dr Cook has received an honorarium from Intavent Orthofix Ltd, manufacturers of the laryngeal masks and has advised a number of airway companies.