Virtual Disaster Medicine

Training Center (VDMTC)

Module 14

Advanced Airway Techniques

Part 2 - New Generation Supraglottic Ventilatory Devices

Classification of Supraglottic Ventilatory Devices

CUFFED PERIPHARYNGEAL SEALERS - AMBU LARYNGEAL MASK

History

In the fall of 2002, the Danish medical device manufacturer, Ambu A/S (Ambu Inc, Glen Burnie, MD) - primarily known for the invention of the manual resuscitator some 50 years ago - was in the process of looking for new clinical areas where the company could utilize its experience within airway management and unique production capabilities.

After a series of visits to anesthesiology departments and interviews with experienced users of laryngeal masks concepts currently on the market.  Ambu and a group of internationally renowned anesthesiologists designed a laryngeal mask to be used under routine anesthesia that offered new benefits to its users.  The result, the Ambu Laryngeal Mask, was commercially launched globally in February of 2004.

Device Description

The Ambu Laryngeal Mask (ALM) is a sterile, single-use product made of polyvinylchloride (PVC), molded in one piece, featuring a special build- in curve that carefully replicates natural human anatomy (Figure 2).  The curve ensures that the patient’s head remains in a natural, supine position when the mask is in use.  Together with the reinforced tip, the curve also facilitates insertion of the mask, without extra stress on the upper jaw.  Additionally, internal ribs built into the curve give the airway tube the flexibility needed to adapt to individual anatomical variances and a wide range of head positions.

It is molded in one piece with an integrated inflation line and no epiglottic bars on the anterior surface of the cuff.  The cuff is eliptical and is shaped to reside in the hypopharynx at the base of the tongue.  Its curved shape and design without epiglottic bars allows easy access for flexible fiberoptic devices.  The product is sterile and latex-free and is available in both adult and pediatric sizes 1-5.  The proper size is based according to the weight and size of the patient (Table 3). 

Table 3 - Ambu Laryngeal Mask size and cuff volume (used with permission from Ambu A/S)

Insertion Technique & Device Removal

It is important that the individual who inserts and/or ventilates through the ALM is familiar with the warnings, precautions, indications, and contraindications in the use of this device.  Before insertion, the following points are of the highest importance:

• The size of the ALM must be appropriate for the patient.  Use the guidelines from Table 3 combined with clinical jugdement to select the correct size.  Consideration should also be given to the patient’s experience with the device and the size used.
• Check for correct cuff deflation and lubricate the posterior surface of the device with a water soluble lubricant.
• Always have a spare ALM ready for use.
• Excess force must be avoided at all times.
• Preoxygenate and implement standard monitoring procedures.
• Ensure an adequate level of anesthesia (or unconsciousness) before attempting insertion.  Resistance or swallowing may indicate inadequate anesthesia and/or inappropriate technique.  Inexperienced users should choose a deeper level of anesthesia.
• Insert ALM in a similar fashion as previously described for the traditional LMAs in Chapter 21.  When the mask is fully inserted, resistance will be felt.
• If the cuff fails to flatten or curls over as it is advanced, it is necessary to withdraw the mask and reinsert it.  In case of tonsillar obstruction, a diagonal shift of the mask is often successful.

Indications and Advantages

The ALM is intended for use as an alternative to the facemask for achieving and maintaining control of the airway during routine and critical anesthetic procedures in fasted patients.  It may be used where unexpected difficulties arise with airway management and even preferred in some critical airway situations.  The ALM may also be used to establish a clear airway during resuscitation in the profoundly unconscious patient with absent glossopharyngeal and laryngeal reflexes who may need artificial ventilation.  The device is not intended for use as a replacement for the ET, and is best suited for use in fasted surgical procedures where tracheal intubation is not deemed necessary.

The ALM features an extra soft cuff.  The cuff is flexible and the tip is reinforced.  These features facilitate insertion and also prevent the tip from folding during insertion.  The cuff, mask and airway tube of the ALM are not glued together but molded in a single unit, thus preventing the mask from separating during use.  The one-piece molding process also ensures that the product is free from ridges that can scratch the walls of the patient’s airways during placement.

Disadvantages

Given that airway pressures should be limited to no greater than 20–25 cm H₂O, the ALM may not be appropriate for patients with reduced lung compliance or increased airway resistance.  The major disadvantage of the device is that it does not protect against aspiration and does not secure the airway as effectively as the tracheal tube.  In addition, the ALM can not prevent nor treat airway obstruction at or beyond the larynx.

Comparison to Face Mask Ventilation & Endotracheal Intubation

In contrast to the face mask, the use of the ALM is associated with less dead space ventilation and no gastric inflation, if reasonable airway pressures are used.  Furthermore, it allows the anesthesiologist to have their hands free for other important tasks.  Compression of eyes and facial and infraorbital nerves is avoided, and operating room pollution from vapors and anesthetic gas is less likely.

Compared to the ET, the ALM is easier to place, avoids laryngoscopy and its associated problems, and is less invasive.  Furthermore, the insertion of this device does not require the use of muscle relaxants.

Guide to Endotracheal Intubation

The ALM may be used as an intubation conduit.  This may be performed by loading an Aintree airway exchange catheter (Cook Critical Care, Bloomington, IN) onto a fiberoptic broncoscope (FOB) and then passing it into the lumen of ALM.  This can be performed either with or without the use of a Bodai adapter (Sontek Medical, Lexington, MA).  The use of the Bodai adapter allows oxygen and gas administration via the attached breathing circuit during the exchange of the ALM to an ET.  When the device is correctly positioned and the mask opening is opposite the vocal cords, the device directs the FOB directly towards the larynx.  Once the FOB has passed through the vocal cords, the Aintree catheter can be advanced into the trachea until the carina is visualized.  The FOB should then be removed.  If oxygenation is necessary at this point, either one of the Rapi-Fit® adapters packaged with the device can be utilized to administer oxygen.  The cuff of the ALM is then deflated and removed over the catheter.  Using direct laryngoscopy, an appropriately sized ET should be passed over the catheter and into the trachea.  Once successfully placed, the catheter can be removed.  Confirmation of tracheal placement should be performed by capnography and chest auscultation.  Blind intubation through the ALM by simply advancing an ET through it or by using a bougie guide may be successful, but passage into the trachea is not consistently obtained, so the above described technique is far preferable.

Medical Literature

A multicenter study of the clinical performance of the ALM was conducted by Hagberg et al.⁴⁵ to evaluate the ease of insertion, insertion success, airway seal and ventilation.  Device placement was successful in all 118 nonparalyzed, anesthetized patients on the first or second attempt (92.4% and 7.6%, respectively).  Adequate ventilation was achieved in all patients and the vocal cords could be visualized by fiberoptic endoscopy in 91.5% of patients.  Complications and patient complaints were minor and were quickly resolved. They found that the curvature of the tube facilitates insertion and the large, soft cuff allows a higher orophangeal leak pressure than is commonly found in other laryngeal masks, thus it can be used more safely for controlled ventilation.  In addition, the tip of the ALM is reinforced to avoid folding that can lead to air leakage, a common problem with other laryngeal mask airways.

In one study center, ventilation using the ALM in different head positions was evaluated.  Gentzwuerker et al.⁵⁹ evaluated the stability of the device in 30 patients in 5 different head positions: 1) head on a standard pillow, 2) head rotated 90° to the left side, 3) head rotated 90° to the right side, 4) head with chin lift on a standard pillow, and 5) head flat on a table without a pillow.  No changes in the performance of the device of ventilatory criteria were documented with any position changes.  Thus, the ALM may be a useful supraglottic airway for cases in which head movement may be necessary for surgery.

Frankensen et al⁴⁶ compared the performance of the uLMA and the ALM in 80 patients undergoing minor routine gynecologic surgery.  They demonstrated that the time of insertion and failure rate was comparable.  Additionally, blood gas samples and ventilation variables revealed sufficient ventilation and oxygenation with either device.  Again, airway leak pressures were higher with the ALM as compared to the LMA- Unique (18 vs. 16 cm H₂O median, and 12-38 vs. 5-28 cm H₂O range; p< 0.013).  No gastric inflation was found to occur with either device nor was postoperative airway morbidity comparable.

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