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 - SOFTSEAL^TM LARYNGEAL MASK

History

The SoftSeal™ Laryngeal Mask (SSLM) is another new disposable supraglottic airway device (Smiths Medical ASD, Keene, NH/Smiths Medical, Hythe, Kent, England) which was developed through the Smiths Internal Research & Development group and is covered by several patients.

The project development for this mask began in November of 1998.  At that time, it was planned to use an extruded tube portion attached to a molded shoe with a blow molded cuff, similar to the existing disposable uLMA.  The first prototype added a “ski tip” form at the nose which was intended to help guide the tube around the oropharynx and into position.  A new method of blow molding the cuff of the device became necessary in order to embed the inflation line for the cuff into the wall of the tubing.  The development of this aspect took a considerable period of time.

The second prototype of the SSLM was developed in September of 2000.  The “ski tip” had been removed, as it has actually increased the impact of forces on the rear of the oropharynx, The heel at the back of the cuff was raised to retain the inflation line, which was also intended to provide a natural position for the finger when used to insert the device using the finger technique, as described by Brain.⁴⁷

The third prototype of the SSLM appeared in January of 2001.  The connector of the device had evolved to include a “knurled” edge to provide an improved grip for clinicians when connecting and disconnecting the device.  Further detail changes around the tip were also incorporated which utilized ultraviolet activated glue.  An artificial oropharynx was developed in order to test the device prior to any clinical use, which allowed measurement of the forces applied on the hard and soft palates, the rear pharyngeal wall, and against the laryngeal inlet.  Following testing of this prototype in the model oropharynx, further design modifications were made, including smoothing the joint between the tube and the shoe and a reduction in the heel height.  A subsequent prototype of this new design was used to perform cadaver studies in Belgium and the US during March of 2001.  Following these trials, future modifications were developed, including, lowering the tip of the shoe below the upper edge of the cuff and eliminating the thickened step in the wall.  Additionally, the shoe and tube were also made as one piece.

The last prototype of the SSLM has a lower lip which allows enhanced flexibility, resulting in measured insertion forces similar to those achieved with the cLMA.  The connector has a more scalloped design.  All of these aspects were combined in the pre-production prototypes used for user evaluation trials in Australia, Sweden, South Africa, and Canada and continued into the product launch.  The final product was commercially launched in Australia in May of 2002.  It was launched in January of 2003 in the US.

Device Description

The SSLM is a tubular oropharyngeal airway with a mask and an inflatable peripheral cuff attached to the distal end (Figure 3).  It is designed to produce an airtight seal around the laryngeal inlet and so provide a secure airway suitable for spontaneous or controlled ventilation during general anesthesia.  It can be inserted without laryngoscopy and paralysis in most cases.  Once in place, it provides more secure airway control than with a facemask and there is no need to support the patient’s chin, allowing “hands free” airway management.

The device is available in 7 sizes, as shown in Table 4.  The proper size is based according to the weight and size of the patient.  In general, the size indications for adults are a #3 for small females, a #4 for most males and females and a #5 for larger male patients.

Table 4 - SoftSeal^TM size chart (used with permission from Smiths Medical, Inc.)

Insertion Technique & Device Removal

Prior to insertion, the valve depressor should be removed from the inflation valve and the integrity of the cuff and inflation system should be checked by deflating the cuff with a syringe and re-inflating with the maximum recommended volume of air (see Table 5).  The tube and cuff should be examined for any signs of damage and the lumen should be free of any blockage.

Table 5 - SoftSeal^TM maximum recommended air volume (used with permission from Smiths Medical, Inc.)

Although there are currently many insertion techniques in use, insertion of the SSLM with the partially inflated cuff technique (approximately 30 cc ambient air) is recommended to provide optimal results.  The valve depressor should be replaced onto the inflation valve to allow the cuff to return to atmospheric pressure.

A sterile water-based gel lubricant should be used to lubricate the posterior surface of the laryngeal mask just prior to insertion.  Application of lubricant to the anterior surface of the mask should be avoided, as this may cause aspiration of excess lubricant or tube blockage.  Also, lidocaine is not recommended as a lubricant as it may lead to an increase in some postoperative complications⁴⁸ and toxicity in pediatric patients.

Just prior to insertion, the valve depressor should be removed to ensure that the cuff has retained an inflated appearance with no wrinkles or depressions.  If not contraindicated, the patient’s head should be placed in the “sniffing position” (neck flexed and head extended).  If a muscle relaxant was administered prior to insertion, use of triple airway maneuver (mouth opening, head extension, jaw thrust) should decrease the incidence of epiglottic downfolding.⁴⁹

The device should be held between the fingers and thumb of the dominant hand the blue line on the tube aligned midline with the nasal septum upper lip to confirm direct orientation.  The top should be directed against the hard palate, as during traditional LMA insertion, while performing a jaw lift with the non-dominant hand.  The mask should be advanced into the oropharynx with slight twisting motion to negotiate the tongue and tonsils.  The non-dominant hand should then hold onto the 15mm connector and push the mask into the hypopharynx until resistance is encountered.  Force should never be utilized.

The cuff should be inflated with air until a “just-seal” pressure is obtained.  A maximum intracuff pressure of 60 cm H₂O is recommended to ensure an adequate seal and minimize trauma.  The tube usually moves out of the mouth up to 15 mm and tissues in the neck bulge slightly when the cuff is inflated confirming correct placement.  The device should not be held or secured prior to cuff inflation.

The tube should then be connected to the breathing system and adequacy of ventilation should be assessed.  A bite block should be inserted to prevent occlusion upon emergence and the tube securely taped in position to the patient’s face.

Indications and Advantages

The SSLM may be used in any patient for airway management in whom anesthesia can be safely maintained through a facemask (with the exception of patients with oropharyngeal pathology or abnormal anatomy).  The device can also be used as a “rescue airway” in either the cannot intubate, cannot ventilate (CICV) or cannot intubate, difficult to ventilate (CIDV) scenarios.  Because the SSLM does not provide airway protection, it is advisable to facilitate endotracheal intubation in order to secure the airway, if the patient is considered at risk for aspiration.  The wider ventilation orifice (can accommodate up to a size 7.5 mm ET) and absence of aperture bars could possibly facilitate this procedure.

Use of the SSLM may be considered in an unconscious patient at risk for airway obstruction who may require artificial respiration when endotracheal intubation is unavailable.  The clinician must balance the risk of pulmonary aspiration against the benefits of obtaining an adequate airway / oxygenation of the patient.

Disadvantages

Given that airway pressures should be limited to no greater than 20 – 25 cm H₂O, the SSLM 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 SSLM can not prevent nor treat airway obstruction at or beyond the larynx.

Comparison to Face Mask Ventilation & Endotracheal Intubation

As with the ALM, the use of the SSLM should be associated with less dead space ventilation and no gastric inflation, if reasonable airway pressures are used, as compared to face mask ventilation.  Furthermore, it allows the anesthesiologist to be 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 SSLM 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 SSLM may be used as an intubation conduit.  This may be done by either directly passing an ET through the shaft of the SSLM or loading an Aintree airway exchange catheter (Cook Critical Care, Bloomington, IN) onto a fiberoptic broncoscope (FOB) and then passing it into the lumen of SSLM.  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 and then the FOB removed.  If oxygenation is necessary at this point, either one of the Rapi-Fit® adapters can be utilized to administer oxygen.  The cuff of the SSLM 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 SSLM 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

Several studies have been performed comparing the performance of the SSLM with the uLMA during both spontaneous and positive pressure ventilation.  Brimacombe et al⁵⁰ studied 90 healthy paralyzed, anesthetized patients undergoing routine superficial or peripheral surgery in a crossover fashion, in which both devices were utilized for positive pressure ventilation in each patient.  They found that the uLMA is superior to the SSLM in terms of ease of insertion, fiberoptic position and mucosal trauma, but similar in terms of oropharyngeal leak pressure and ease of ventilation.

In another randomized, crossover study comparing the SSLM and the uLMA in 168 anesthetized, spontaneously breathing patients.  Paech et al.⁵² determined that although both devices performed equivalently with respect to first-time placement, the SSLM was often rated more difficult to insert and more likely to show mucosal trauma.  On the other hand, the fiberoptic view of the larynx was better through the SSLM and it more frequently provided a ventilation seal at 20 cm H₂0.  Also, in contrast to the uLMA, its cuff pressure did not increase during nitrous oxide anesthesia.  In this study there was a larger proportion of females, a smaller mask size was used for both males and females, and the SSLM was inserted with a partially inflated cuff.

When the SSLM was compared to the cLMA, Van Zundert et al⁵³ found that in spontaneously breathing adult patients requiring a size 4 LMA, the new disposable SSLM is an acceptable alternative to the cLMA, resulting in a good laryngeal seal and similar clinical performance.  They also determined that the cuff pressures substantially increased with the cLMA and that there was less trauma to patients using the SSLM, as assessed by the incidence of sore throat in the early postoperative period.  This decreased incidence of both trauma and sore throat may possibly be due to partial inflation of the cuff with ambient room air at 10 mmHg (15 cm H₂O) above atmospheric pressure.  Hagberg et al⁵¹ also demonstrated that partial cuff inflation (30 cc of ambient air) enhances ease of insertion and minimizes mucosal trauma, as previously recommended.

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