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Correspondence

Clinical assessment of use of the Airway Management Device (AMD®)

McGill, F.; Shobba, R.; Stacey, M.; Turley, A.; Hall, J. E.

Author Information
European Journal of Anaesthesiology: February 2004 - Volume 21 - Issue 2 - p 164-165

EDITOR:

The Airway Management Device (AMD®; Nagor Ltd, Douglas, Isle of Man, UK) was developed as an alternative to existing devices such as the laryngeal mask airway for securing the airway in anaesthetized patients [1]. It has two cuffs, originally available in two sizes, selected according to patient size. The lower cuff, when inflated, sits in the hypopharynx to form a seal at the level of the upper oesophageal sphincter. When partially deflated, this cuff allows passage of a catheter into the oesophagus for gastric aspiration. The upper cuff, when inflated, sits at the inferoposterior aspect of the tongue above the laryngeal inlet, forming a low-pressure seal. The airway aperture is between the cuffs.

There are currently insufficient data to assess the efficacy of this device. The manufacturer's information leaflet describes its use in 40 patients [1,2], when the device was successfully used. However, a recent report [3] indicated that difficulties were encountered in its use. As there are conflicting data about the efficacy of the device, it was felt that further clinical assessment was needed. The aim was to assess the ease of insertion of the device, its ability to maintain an airway and the frequency of untoward events in anaesthetized patients.

The Local Research Ethics Committee gave approval, and written informed consent was obtained from the patients. Fifty healthy adults breathing spontaneously during general anaesthesia were studied. Patients were excluded if they had predicted difficult intubation, neck, respiratory tract or alimentary tract pathology, were at risk of pulmonary aspiration or obese.

The size of the AMD® was selected based on the gender of the patient: size 3-3.5 for females and size 4-5 for males. Patients were unpremedicated. After preoxygenation, fentanyl 1.0 μg kg−1 was given and propofol injected using Drage and colleagues' method [4]. When the patient no longer responded to commands, the angles of the mandible were lifted. If there was any motor response to jaw thrust, additional propofol was given until the response was abolished. The anaesthetist opened the patient's mouth: if it was difficult or if coughing, gagging or body movement occurred, additional propofol was given. When it was easy to open the mouth, the AMD® was inserted. The anaesthetic assistant depressed the lower jaw and the AMD® was inserted in the manner recommended by the manufacturer in a single, smooth movement until the deflated upper cuff passed the tongue.

Advancement of the AMD® was terminated when resistance was felt as the lower cuff lodged in the hypopharynx. The upper cuff was inflated: the volume of air used was based on the patient's weight (on a mL kg−1 basis) until an airtight seal was achieved. Auscultation and capnography confirmed correct placement during gentle manual ventilation of the lungs. If inserted incorrectly, the AMD® was removed and reinserted (for a total of three times). If it was still not possible to ventilate at this point, an alternative airway was substituted.

Anaesthesia was maintained with an inhalation anaesthetic agent or total intravenous anaesthesia at the discretion of the anaesthetist. At the end of the operation, the anaesthetic was turned off and the AMD® left in place. The device was removed by deflating the upper cuff when the patient responded to a verbal command to open the mouth.

The mean, standard deviation (SD) and 95% confidence intervals (CI) of the dose of propofol given before insertion of the device were calculated. The number of insertion attempts was noted. The ease of insertion was scored as: easy, moderately difficult, difficult and impossible. Any adverse airway events that occurred using the device were recorded. Oxygen saturation was noted if it fell below 94%.

Fifty patients were recruited: 32 females, 18 males. The mean (SD, 95% CI) dose of propofol injected before AMD® insertion was 3.5 (1.63, 3.04-3.96) mg kg−1. Insertion was easy in 43 patients (86%), moderately difficult in six (12%) and impossible in one (2%), where a laryngeal mask had to be used instead. Correct placement of the AMD® was achieved at the first attempt in 31 patients (62%). Complications occurred in the other 19 patients - most necessitating anaesthetic intervention, including further doses of propofol, reinsertion of the AMD® and use of an alternative airway, e.g. the laryngeal mask.

There were four cases of airway obstruction during induction (Table 1), three of which were resolved with additional propofol and AMD® reinsertion. Three patients developed severe laryngospasm, with one needing succinylcholine and insertion of a laryngeal mask. Two patients were settled with continuous positive airway pressure and additional propofol.

Table 1
Table 1:
Airway complications with the AMD® after insertion, during maintenance and on emergence from anaesthesia.

During maintenance, the main problem encountered was airway obstruction (29%) (Table 1). In six cases, jaw thrust corrected the problem. However, the AMD® had to be removed in five patients and an alternative airway was inserted (laryngeal mask in four patients, Guedel airway in one patient). In the other three cases of airway obstruction, readjusting or reinsertion of the AMD® solved the problem. Desaturation (SPO2 < 94%) occurred in three patients (6%). Coughing was the only problem noted during emergence (five patients, 12%) (Table 1); it was minor and resolved on AMD® removal. Blood on the device was seen in three cases.

Recent unpublished studies [1,2] have shown that the AMD® can be used safely in spontaneously breathing patients with minimal interventions and complications. This contrasts with the results of the present study of the device. Insertion of the AMD® was not necessarily difficult. Although direct comparison was not made here, the rate of failure to insert the AMD® (2%) was similar to the more commonly used laryngeal mask airway (0.3-4%) [5]. The majority of induction problems were easily dealt with by simple measures, although two patients required laryngeal masks to be inserted, one where the patient developed severe laryngospasm, the other where the AMD® was impossible to insert. The latter patient was noted to have a small mouth (Mallampati score 2) with a bridge and crowns, making it difficult to pass the proximal cuff.

One of the aims of the AMD® is to produce a reliable, patent secure airway [1,2]. Unfortunately, the main problem during maintenance was airway obstruction (29%). Jaw thrust alone solved the problem in 42% of patients, but this occupied the anaesthetist, thus defeating the object of a hands-free airway. The cause of the obstruction was not clear. The upper cuff is designed to sit at the posteroinferior aspect of the tongue - one of the purposes of this cuff is to elevate the tongue and epiglottis, creating a clear airway as in a jaw thrust manoeuvre [6]. The oval cross-section of the upper cuff is meant to help secure a patent airway [2]. It is possible that the tongue is not adequately displaced on cuff inflation with the recommended volume. In addition, the direction of tongue displacement plays a major role in maintaining a clear airway. Airway obstruction is more likely if the tongue is displaced downwards, which is theoretically possible with a large AMD® - or if the AMD® is not inserted far enough beyond the tongue. It is suggested that the shape and size of the upper cuff may be a significant cause of airway obstruction. Airway obstruction may also be due to failure to locate the aperture of the AMD® at the level of the laryngeal inlet or obstruction of the laryngeal inlet by the epiglottis [7] due to malposition or incorrect airway size.

The AMD® may have a role, perhaps even in emergency anaesthesia: it was easy to insert and offered the possibility of emptying the stomach. However, its use is not recommend until modifications are made and fully tested.

F. McGill

R. Shobba

M. Stacey

A. Turley

J. E. Hall

Department of Anaesthetics; University of Wales College of Medicine; Cardiff, UK

References

1. O'Neil MJ. Development and Evaluation of a New Airway Management Device in Spontaneously Breathing Anaesthetized Patients. Douglas, UK: Nagor Ltd, 2000.
2. O'Neil MJ. Development and Evaluation of the Airway Management Device (AMD) Including Comparison with Laryngeal Mask Airway (LMA), in Spontaneously Breathing Anaesthetized Patients. Douglas, UK: Nagor Ltd, 2000.
3. Cook TM, Gupta K, Gabbott DA, Nolan JP. An evaluation of the Airway Management Device. Anaesthesia 2001; 56: 660-664.
4. Drage M, Nunez J, Vaughan RS, Asai T. Jaw thrusting as a clinical test to assess the adequate depth of anaesthesia for insertion of the laryngeal mask. Anaesthesia 1996; 51: 1167-1170.
5. Brimacombe JR. Problems with the laryngeal mask airway: prevention and management. Int Anesthesiol Clin 1998; 36: 139-154.
6. Boidin MP. Airway patency in the unconscious patient. Br J Anaesth 1985; 57: 306-310.
7. AMD™ Product Information. Insertion Technique and Airway Management of the AMD (Airway Management Device). Douglas, UK: Nagor Ltd.
© 2004 European Academy of Anaesthesiology