Difficult Airway Management with the Intubating Laryngeal Mask

Abstract

The laryngeal mask airway (LMA) has an established role in difficult airway management as a ventilatory device and airway intubator [1,2], but its latter role is limited because the airway tube is too long and narrow to accommodate a standard sized tracheal tube (TT) and too floppy to optimize alignment with the glottis. In an attempt to overcome these limitations, an intubating laryngeal mask (ILM) has been developed (Intavent Research LTD, Reading, UK). The success rate for blind intubation via an earlier prototype ILM is 92% in normal patients [3]. The new prototype device consists of an anatomically curved, short, wide-bore, stainless steel tube sheathed in silicone, which is bonded to a laryngeal mask and a guiding handle (Figure 1). It has a single moveable epiglottic elevator bar and a guiding "V"-shaped ramp (Figure 2) and can accommodate an 8-mm TT (Figure 3). I report the use of the ILM as an aid to blind tracheal intubation in two patients with difficult airways.Figure 1: The intubating laryngeal mask and silicone tracheal tube with curved tip.Figure 2: The epiglottic elevator bar and "V"-shaped ramp.Figure 3: The bowl of the intubating laryngeal mask showing the curved tip of the tracheal tube pushing open the epiglottic elevator bar.Case Report Case 1 A 53-yr-old, 140-kg, 177-cm woman presented for a laparotomy. On examination, she was grossly obese, with a thick, bull neck, a Mallampati grade IV, and thyromental distance of 8 cm. She had a history of asthma and reflux. No information was available about previous anesthetics. An awake endotracheal intubation was planned using a size 4 ILM (bowl size identical to size 4 LMA). The TT used was an 8-mm straight-cuffed silicone tube with a curved tip. The tube was marked transversely to show the user the point at which the tip was about to lift away the epiglottic elevator bar and the depth at which resistance was felt during insertion. The patient was prepared with 10% topical lidocaine spray and a cricothyroid puncture with 3 mL 4% lidocaine. The ILM was inserted with the cuff fully deflated using a one-handed rotational technique in the sagittal plane with the head and neck in the neutral position [4]. The cuff was inflated with 15 mL air, and a clear airway was obtained. The mask was then steered with the handle until the best seal was obtained, and the lubricated TT was passed blindly into the trachea at the first attempt without resistance. Anesthesia was subsequently induced with propofol intravenously and was otherwise uneventful. The ILM cuff was deflated once the TT was in position. The ILM was removed at the end of the procedure with the TT. When questioned the next day, the patient said that she would be happy to undergo the same technique. Case 2 A 49-yr-old, 68-kg, 170-cm woman presented for an elective laparotomy. She had a history of difficult endotracheal intubation with a high anterior larynx and buck teeth. Tracheal intubation had been previously possible on the third attempt using a bougie, but ventilation via a face mask was easy. On examination, her airway was classified as Mallampati class III with a thyromental distance of 5 cm. She had no history of reflux. Anesthesia was induced by inhalation of sevoflurane, and the size 4 ILM inserted when the patient was deeply anesthetized. The patient was paralyzed with vecuronium to facilitate tracheal intubation, which was accomplished at the first attempt using the technique adopted in Case 1. The ILM was then removed by attaching an extender tube to the TT [5] and then withdrawing the ILM over it using the reverse of the rotational maneuver used to place it. Discussion The ILM has a number of design features that distinguish it from the LMA (Table 1) [6]. The rigid widebore tube permits the mask to be guided during endotracheal intubation and accommodates a normal sized TT. The curved tube permits insertion to follow the palatopharyngeal curve, yet avoids the need for head and neck manipulation and insertion of the finger in the patient's mouth. The integral handle facilitates placement, removal, and positional adjustments during intubation. The "V"-shaped ramp centralizes and guides the TT anteriorly to avoid arytenoid trauma/esophageal placement. The epiglottic elevating bar acts as an epiglottic ramp during insertion and elevates the epiglottis during TT passage.Table 1: Intubating Laryngeal Mask (LM) Design Features and FunctionThe ILM offers a number of potential advantages and disadvantages compared with the LMA. First, it overcomes the dimensional limitations for TTs imposed by the LMA and facilitates guidance of the TT toward the glottis. Second, placement does not require head/neck manipulation or insertion of fingers into the patients mouth. It can also be achieved from any position using the same insertion technique. Third, the guiding handle allows an optimal airway to be sought out and additional force applied to the periglottic tissues if a higher pressure seal is transiently needed. Disadvantages are that the rigid tube may prevent the tip sitting in the correct anatomical position and that the seal may change if the head or neck is moved. Also, the device cannot be inserted if the interdental distance is less than 20 mm. If resistance is felt during tracheal intubation attempts, the position of the ILM should be adjusted to improve alignment with the glottis and to avoid trauma. Once tracheal intubation is accomplished, the ILM may be left in situ with the cuff deflated, or removed if the procedure is prolonged or the device impedes surgical access. Like the standard device, difficulty in viewing the larynx, which often underlies difficulty in intubation, is probably irrelevant to ILM placement, and the device allows positive pressure ventilation to be continued during intubation attempts. The safety and efficacy of the device for prolonged ventilation has not been determined. In summary, these case reports illustrate the potential of the ILM as a temporary ventilatory device and airway intubator in awake and anesthetized patients with abnormal airways.