Single‐use laryngeal masks for the management of unexpected failed intubation

Abstract

We wish to alert colleagues to a potential difficulty with the use of the Intavent LMA®-Unique (Intavent Orthofix, Maidenhead, UK) in the management of failed intubation. A 36-year-old female patient (BMI 46) required immediate laparotomy for concealed haemorrhage, 4 h after an emergency Caesarean section. General anaesthesia was induced using a standard rapid sequence induction. Laryngoscopy, performed first by an SHO, then by an experienced consultant obstetric anaesthetist, revealed a grade 3 view. Tracheal intubation proved impossible and a gum elastic bougie could not be passed. Mask ventilation with an oropharyngeal airway was difficult and so a size three LMA®-Unique was inserted. A good seal was achieved and acceptable ventilation of the lungs was possible. We subsequently attempted to intubate the trachea by passing a 6.0 mm ID cuffed tracheal tube (Mallinckrodt Medical, Athlone, Ireland) through the laryngeal mask airway over a fibrescope, as described in the recent Difficult Airway Society (DAS) guidelines [1]. This proved impossible, as the tracheal tube could only be advanced about 90% of the way along the lumen of the laryngeal mask airway's tube, despite copious lubrication. The airway was secured by insertion of a 5.0 mm microlaryngeal tube over a fibrescope via the laryngeal mask airway and the patient suffered no ill effects. We subsequently investigated whether this problem was common to all single-use laryngeal mask airways. We obtained a size 3 and size 4 version of each of the various laryngeal masks available in our hospital (LMA®-Unique, Intavent Orthofix; LMA®-Classic, Intavent Orthofix; Marshall LAD™, Marshall Products Ltd, Bath, UK; Intersurgical Solus™, Intersurgical Ltd, Wokingham, UK; Ambu® Laryngeal Mask, Ambu Ltd, St Ives, UK), and attempted to pass a well lubricated 6.0 mm tracheal tube, with cuff fully deflated, through them. The results appear in Table 1. With the exception of both sizes of LMA®-Unique and the size 3 Ambu® product, passage of the tracheal tube was achieved with ease. We initially postulated that the tube material of the laryngeal masks might explain the differences. However, as Table 1 shows, there is no common culprit. Other possible reasons might be differing frictional characteristics of the inner surface of the tube, or differing calibres of the tubes. In the case of the size 3 Ambu®, the preformed angulation appears to be a major factor. Of interest, the Intavent Orthofix product is the only one to have aperture bars, another potential hindrance to passage of a fibrescope or tracheal tube, although in our test, the tracheal tube did not even reach them. The DAS Guidelines refer specifically to the re-useable LMA®-Classic. They suggest the use of a microlarygeal tube via this device, but only on the grounds of length; it is stated that a 6.0 mm tracheal tube will pass through a size 3 LMA®-Classic (as confirmed in our testing). They state clearly that the role of single-use laryngeal masks in this setting has yet to be established. Our experience goes some way towards clarifying matters. Colleagues need to ensure that the equipment on their difficult intubation trolley will do what they expect in a crisis. We have copied our findings to Intavent Orthofix, the Difficult Airway Society, and to the Medicines and Healthcare products Regulatory Agency.