Virtual Disaster Medicine

Training Center (VDMTC)

Module 14

Advanced Airway Techniques

Part 2 - New Generation Supraglottic Ventilatory Devices

Classification of Supraglottic Ventilatory Devices

CUFFED PHARYNGEAL SEALERS - LARYNGEAL TUBE^TM

History

The Laryngeal Tube™ (LT) (VBM Medizintechnik, Sulzam Neckar, Germany) and King Laryngeal Tube™ (King Systems Corp., Noblesville, Ind) are supraglottic airway devices which were introduced to the European market in 1999¹⁴ and to the US in February of 2003.

Device Description

The LT consists of a silicon reusable airway tube provided with two cuffs (pharyngeal and esophageal) a single balloon for pressure control^14,15 and a 15 mm standard male adapter (Figure 8), which is designed to be reused up to 50 times.  The airway tube is short and “J” shaped, has an average diameter of 11.5 mm and a blind tip.  Six sizes, suitable for neonates up to large adults, are available^14,15 (Table 8).  LT size selection must be based on the patient’s weight from size 0 to 2, and on height from size 3-5.  The disposable version (King LTD) is currently being sold in sizes 3-5 worldwide.  Pediatric sizes will become available in the near future.

Table 8 - LT size recommendations (used with permission from King Systems).

After device insertion, the proximal cuff lies in the hypopharynx and the distal in the upper esophagus.  Both cuffs are high volume and low pressure to avoid ischemic damages and permit a good seal.  The original version of the LT was designed with a single ventilation opening between the 2 cuffs in the ventral part of the tube.  This version also had 2 separate inflation lines for the 2 cuffs.  Subsequent changes in the design of this device prior to its launch in the US included 2 ventilation outlets rather than the one located between the 2 cuffs.  The proximal cuff is protected by a bend located in a “V” dent of the pharyngeal cuff.  With cuff inflation, soft tissue is deflected from this opening, helping to maintain a patent airway.³  A wedge shaped block closes the tip of the tube, thus diverting the inflated mixture to the trachea.  The cuffs should be inflated, with the aid of the laryngeal cuff pressure gauge, to 60 cm H₂O.  Due to a single inflation line, both cuffs will inflate simultaneously.

Additionally, there were 2 side eyelets (one on either side of the main ventilation orifices).  The latest version of the LTD now has 3 side eyelets on each side to allow improved collateral ventilation should the epiglottis obstruct the main ventilation orifice (Figure 9).  This version has also been manufactured 1.0 cm longer to facilitate deeper placement of the device, thus assuring proper positioning of the two main ventilation orifices and location of the proximal cuff beneath the tongue so that the epiglottis is more likely to be raised with cuff inflation in much the same manner as with a Macintosh Laryngoscope blade.

The Laryngeal Tube Suction™ (LTS) is a double-lumen silicon LT that incorporates a second esophageal lumen placed behind the ventilatory lumen (Figure 10).  This second lumen represents a relief valve for increases in gastric pressure which permits gastric suctioning and egress of gastric contents.¹⁷  Although this version of the LT is FDA 510(k) approved in the US, the LTS is currently only available in Europe.  Clinical trials involving a disposable version that differs in design from the silicon or reusable LT will soon be conducted in the US.

Insertion Technique & Device Removal

Before each use the non-disposable LT must be cleaned and sterilized.

The LT must first be washed in warm water using a mild soap or a diluent with 8-10% sodium bicarbonate solution.  The LT must not be exposed to any chemicals, disinfectants or cleaning agents not recommended for use with silicon.  The LT must then be carefully inspected to ensure that all visible foreign matter has been removed.  All air should be removed from the cuffs with a syringe, prior to its sterilization.  When the cuffs are tightly deflated, the device may be placed in an appropriate autoclave-proof bag before autoclaving.  Steam autoclaving is the only method recommended for the sterilization of this device.  The maximum autoclave set-point temperature should not exceed 134°C at 2.4 bar for 10 mins.  After autoclaving and before each use the cuffs of the LT should be checked for any leakage.

The LT should be placed after induction of anesthesia when the patient is apneic, loses his eyelash reflex and there is no resistance to manipulation of the lower jaw.  If no muscle relaxing agent is used, anesthesia should be deep enough to obtund the airway reflexes.  An appropriately sized LT should be chosen according to the selection criteria described above.  Before insertion, the cuffs must be fully and correctly deflated and lubricated.  A neutral head position is ideal although the sniffing position with jaw lift, makes it easier to go around the corner in the posterior pharynx.  The device characteristics ensure the placement of the tube in any given position of the head and of the operator.  The LT should be held in the dominant hand and inserted blindly along the midline of the tongue with the tip against the hard palate in the caudal direction.  Then, it should be passed smoothly along the palate into the hypopharynx until resistance is felt.

The proximal and distal cuffs should then be inflated with the aid of the Cuff Pressure Gauge (King Systems) to 60 cm H₂O.  If it is not available, or time is of the essence, the cuffs can be inflated with the aid of its dedicated syringe (Table 9).  Due to the specially designed inflation line, the proximal cuff is first filled stabilizing the tube.  When the proximal cuff adjusts to the anatomy of the patient, the distal cuff automatically inflates.  The LT can be now connected to the breathing system.  Indicators of correct LT placement are: auscultation of bilateral lung sounds, bilateral chest excursion, absence of gastric insufflation, and capnography.  When the LT is correctly positioned, the bite-block can be attached to the tube.

Table 9 - Maximum LT cuff volumes (used with permission from King Systems).

The correct placement of the LT may be verified using a test with a lightwand (Trachlight^TM) without the metallic stylet.  The lightwand can be inserted into the LT and advanced through it until a faint glow can be seen above the thyroid prominence.  It indicates that the tip of the lightwand is just in front of the laryngeal inlet.  The lightwand can be advanced still further until a well-defined circumscribed glow is seen in the anterior neck slightly below the thyroid prominence.  When the LT is correctly positioned, the lightwand tip easily enters into the glottic opening showing a well-defined circumscribed glow.  The Trachlight^TM test must be considered negative when transillumination shows a glow with halo near the thyroid prominence.  This could be due to the position of the Trachlight^TM tip lying against the epiglottis or the glosso-epiglottic fold.  The visualization of a lateral glow indicates that the hole for ventilation is not in front of the laryngeal inlet even though ventilation may be effective.

After LT placement, respiration is initially supported by manual ventilation and the patient is allowed to resume spontaneous ventilation.  Even when spontaneous ventilation is planned, it is suitable to initially use positive pressure ventilation, thus assuring good ventilation, in addition to providing information about correct LT placement.

The LT is well tolerated until the return of the protective reflexes.  Slight cuff deflation at this point allows better toleration of the oropharyngeal cuff.  The device should be removed with the patient either deeply anesthetized or totally awake, otherwise laryngospasm, coughing or gagging may occur.  Before removal of the device the cuffs should be completely deflated.  Inadequate cuff deflation can make removal difficult, risking cuff damage and discomfort for the patient.

Indications and Advantages

The LT is designed for use during spontaneous or controlled ventilation.  The slim profile of the LT allows easy insertion with little mouth opening, thus it can be considered for airway management in patients with restricted mouth opening.  The insertion is relatively easy and guarantees a clear airway in most patients on the first attempt, thus extensive training is not necessary. 

Due to the form and length of the tube, an inadvertent endotracheal intubation should not occur.  The LT has an extreme low incidence of trauma with respect to sore throat, hoarseness or blood compared to other supraglottic airway devices.  This is due to the soft tip, soft cuff material and low cuff pressures.  High volume, low pressure cuffs provide a good seal and protect from ischemic damage and the presence of only one pilot balloon allows quick cuff inflation quicker, and it is useful in emergency situations.

As a supraglottic device, the LT can be used to detect laryngopharyngeal activity and can provide information about the depth of anesthesia in non-paralyzed patients.  Inactivity of the vocal cords is considered an important indicator of depth of anesthesia in non-paralyzed patients.  As with any SGA, surgical stimulation can cause laryngospasm.  Vocal cord activity may be detected by alteration of capnography and airway resistance.  If vocal cord activity is present, the flow-volume monitoring shows alterations of the loop due to the laryngeal resistor component.

Additionally, the ventilation can be controlled by the LT during attempts at fiberoptic nasotracheal intubation.  Both the FOB and the ET can be advanced through the nose into the oral cavity without deflating the cuffs of the LT.  Once endotracheal intubation is determined to be successful, the cuffs of the LT can be deflated and the device removed.

Disadvantages

Presently, it is not prudent to use the LT in anesthetized patients at increased risk of pulmonary aspiration of gastric contents.  Additionally, the LT may not be appropriate in patients with poor lung compliance or increased airway resistance, or in patients with lesions of the oropharynx or epiglottis.  Lastly, the LT can not prevent nor treat airway obstruction at or beyond the glottis.

Comparison to Face Mask Ventilation and Endotracheal Intubation

Due to the presence of the ventilation holes and the interval wedge shaped block, 3 maneuvers are possible: 1) aspiration of blood and/or secretions, 2) passage of a FOB, and 3) passage of a tube exchanger.  Compared with the face mask, the LT allows better access to the airway, resulting in minimal dead space and gastric inflation.  Furthermore, the LT allows the anesthesiologist to have his hands free and to reduce the environmental pollution from vapors and anesthetic gas.

Guide to Endotracheal Intubation

The trachea can be intubated using small sized ETs (up to 6.5 mm) which can be passed blindly through the LT.  The ET connector must be removed and the tube must be well lubricated.  The tip of the ET is gently advanced forward until it passes through the glottic opening.  Possible resistance can be due to incorrect positioning of the LT, epiglottis obstruction of ET passage or inadequate lubrication of the ET.  This procedure can be visualized by video laryngoscopy using the DCI Video Intubation System (Karl Storz Endoscopy, Culver City, CA).  Once the ET is positioned, the cuffs of the LT must be deflated and the device can then be removed.  The shorter tube shaft on the LT, compared to the LMA, allows the ET to be inserted far enough so that the cuff can be placed as desired in the trachea without removal of the LT.  Unless indicated otherwise, the LT should remain in place with both cuffs deflated after tracheal intubation has been performed.  The disadvantage of this procedure is that the diameter of the ET is limited by the LT size. Since removal of the LT over the ET can be problematic, exchanging the ET and LT using a tube exchanger and then passing a larger sized ET, if desired and appropriate, is recommended. 

To overcome this problem, a tube exchanger may be used.  Tracheal intubation via the LT can be performed also with fiberoptic placement of the Aintree airway exchange catheter (Cook Critical Care, Bloomington, IN) (See Chapter 47).  Throughout the procedure, oxygen administration can continue via the LT, until its removal using a Bodai adapter (Sontek Medical, Lexington, MA).³²

Medical Literature

Most available trials have used earlier revisions of the LT, rather than the currently available device.  Nonetheless, the results of these trials are mostly positive.  Both Doerges and Asai, along with their colleagues, determined that after blind insertion, the device provides a patent airway in the majority of patients at the first attempt.^17,18  The LT tube can be inserted quickly without extensive training; it is considered a suitable airway management device with a high rate of successful insertion, requiring a mouth opening as limited as 23mm.^19,20  LT placement is easy²⁰ and its acceptance among physicians, nurses and paramedics is high.^6,12  Simple handling, aspiration protection are its substantial advantages.¹⁷  Correct LT positioning may require more adjustments in patients with an increased BMI.²⁴

As compared to the LMA, insertion time is comparable.¹⁷  Asai et al.⁷⁶ reported the successful use of the LT in 3 patients in whom insertion of the LMA had failed.  These authors hypothesized that the success and failure might have been related to a difference in the width of these 2 devices.  The pharyngeal space was narrowed by swollen tonsils, goiter and redundant oropharyngeal tissue, thus, they recommend that when LMA insertion is difficult or impossible due to a narrowed pharynx, insertion of the LT may be attempted, before considering endotracheal intubation.

Halothane, enflurane, isoflurane, sevoflurane, desflurane and total intravenous anesthesia may be used for maintenance of anesthesia with the LT.  Nitrous oxide may be used to maintain anesthesia although cuff pressures should be monitored with its use.^30,31 A rise of 15cm H₂O in the intracuff pressure 30 min after its insertion, caused by the diffusion of nitrous oxide into the cuff has been demonstrated.^30,31

Ventilation achieved with the LT is comparable to that obtained with other SGAs.  In fact, its seal pressure has been found to be better than the standard LMA²¹.  It provides a good airway seal to 30cm H₂O of airway pressure^18,26 and has been shown to be efficacious during mechanical ventilation in adult and pediatric patients undergoing elective surgery.^14,18,27