Module 14
Advanced Airway Techniques
Part 2 - New Generation Supraglottic Ventilatory Devices
Introduction
In the past, the choice of an
airway device essentially was limited to the facemask or the
endotracheal tube (ET).1
Tracheal intubation is the overall accepted “gold standard” of
securing the airway and providing adequate ventilation.
However, training in tracheal intubation requires time,
appropriate instruments, and adequate circumstances with respect
to space and illumination. Furthermore, tracheal intubation
requires continued practice and carries with it its own set of
complications.
The practice of airway management
has become more advanced in recent years. This advancement is
demonstrated by the introduction of many new airway devices,
several of which have been included in the American Society of
Anesthesiologists (ASA) Difficult Airway Algorithm.43
The standard laryngeal mask airway, LMA-Classic™ (cLMA; LMA
North America, Inc., San Diego, CA) was introduced into clinical
practice in 1988 and rapidly transformed airway management.
Since that time, and particularly in the last five years, there
has been an explosion of new supraglottic airway devices
designed to compete with the cLMA, particularly single-use
devices. There are several driving forces for the
introduction of single-use devices including the concern over
sterility of cleaned, reusable devices (e.g. elimination of
proteinaceous material and the risk of transmission of prion
disease) and the inability to recycle the device enough to be
cost effective. There are more than a dozen manufacturers
of the single use LMA (LMA Unique or uLMA), yet only those
manufactured by Intavent or LMA North America have the
epliglottic bars at the distal end of the airway tube due to
patent reasons.
Supraglottic airway (SGA) is a
general term that includes airways with and without sealing
characteristics. In a recent editorial, Brimacombe40
recommends that the term “extraglottic” airway be used instead
since many of these devices have components that are
infraglottic (hypopharynx and upper esophagus). Nonetheless,
this book describes all airway devices that have a ventilation
orifice(s) above the glottis as “supraglottic” and those which
deliver anesthetic gases/oxygen below the vocal cords (e.g.
transtracheal jet ventilation, cricothyrotomy as “infraglottic.”
Both Brimacombe (Table 1) and
Miller (Table 2) suggest there be a classification system for
this increasing complex family of devices. According to Miller,41
there are 3 main sealing mechanisms: cuffed perilaryngeal
sealers, cuffed pharyngeal sealers, and cuffless anatomically
preshaped sealers. The explanation for each provides reasons
for the differences observed in the sealing pressures achieved
with each of the different types of devices. Further
subdivision can be made considering whether the device is
single-use or reusable and whether protection from aspiration of
gastric contents is offered. Figure 1 illustrates the 3 sealing
mechanisms, the force vector being determined by the airway
pressure in the pharynx proximal to the sealing site.
Table 1: Classification of Extraglottic Airway Devices by 1)
Presence/Absence of a Cuff, 2) Oral/Nasal Route of Insertion,
and 3) Anatomic Location of the Distal Portion (Brimacombe:
Anesthesiology 2004;101:559)
|
Cuffed, orally-inserted laryngopharyngeal airways
Williams airway intubator*
Patil oral airway*
Ovassapian fiberoptic intubating airway*
Combined oraopharyngeal airway and dental pack
Modified Connell airway
Mehta’s cuffed oropharyngeal airway†
Cuffed oropharyngeal airway† |
Cuffed, orally-inserted hypopharyngeal airways
Classic LMA‡
Flexible LMA‡
Intubating LMA*
Diposable LMA‡
ProSeal LMA‡
Glottic aperture seal airway‡
Streamlined pharynx airway liner‡
SoftSeal™ laryngeal mask‡
Laryngeal Tube™ airway†
Laryngeal Tube™ suction†
Airway management device†
Pharyngeal airway express†
Cobra pharyngeal lumen airway† |
|
Cuffed, orally-inserted esophageal airways
Pharyngeal tracheal lumen airway†
Esophgeal tracheal combitube |
|
Uncuffed, nasally-inserted laryngopharyngeal airways
Variable flange nasopharyngeal airway
Linder nasopharyngeal airway |
|
Cuffed, nasally-inserted laryngopharyngeal airways:
Boheimer’s cuffed nasopharyngeal airway† |
Uncuffed, orally-inserted esophageal airways
Tracheo-esophageal airway |
Many of the names of extraglottic
airway devices do not fit with this classification system. For
example, the distal ends of the “Patil oral airway” and the
“Linder nasopharyngeal airway” are in the laryngopharynx and not
in the oral cavity and nasophaynx, respectively. There are no
extraglottic airway devices whose distal portion is intended to
sit in the oral cavity, nasal cavity, or nasophaynx.
*Primary function as an airway intubator; †proximal
pharyngeal cuff; ‡periglottic cuff
LMA=Laryngeal mask airway
Table 2: Miller’s Supraglottic
Classifications (adapted from Miller: Anesth Analg 2004; 99:1553-9).
|
|
Cuffed Perilaryngeal Sealers |
Cuffed Pharyngeal Sealers |
Cuffless Pre-shaped Sealers |
|
Without Directional Sealing |
With Directional Sealing |
Without Esophageal Sealing Cuffs |
With Esophageal Sealing Cuffs |
|
Devices |
LMA
ILMA
SSLM
Ambu
LS
ILA |
PLMA |
CobraPLA |
LT
LTS
ETC |
SLIPA |
|
Sealing Mechanism |
Relies on simple opposition of the cuff that surrounds the larynx. |
Sealing site is at or around the entrance of the larynx. |
Pharyngeal cuff seals at the base of the tongue. |
Anatomically pre-shaped
hollow airway which seals the outlet from the pharynx at
the base of the tongue to the entrance to the esophagus,
as a result of the resilience of the walls of the shaped airway. |
|
Advantages |
1. Minimal risk of precipating laryngospasm
2. Well tolerated at lower anesthetic levels |
1. Higher seal pressures
2. Decreased risk of regurgitated fluid entering airway channel |
1. Better sealing pressures
2. Pressure exerted perpendicular to airway channel |
1. Minimizes aspiration risk
2. Most provide access to esophagus |
1. Hollow structure provides aspiration protection by storage of
regurgitation liquid
2. Safe to suction regurgitated liquid without risk of laryngospasm
3. Preshaped airway provides specific positioning and a stable airway
4. Easier to use
5. No NO2 influence
6. Able to insert through limited mouth opening |
|
Disadvantages |
1. Low seal pressures
2. Little storage space for regurgitated liquid
3. Increased risk of gastroesophageal insufflation
4. No protection from aspiration
5. Backward-slanting profile can get caught in back of mouth |
1. Harder to insert
2. More easily rotated out of position
3. Folding of tip can occur upon insertion, occluding the drainage tube |
1. No sealing of the downward outlet increasing risk of gastroesophageal insufflation
2. Reliance based on tone of gastroesophageal sphincter
3. No protection from aspiration
4. Increased need for repositioning |
1. Increased potential for mucousal trauma due to stiffer tube
2. Congestion of tongue with excessive increases in cuff pressure and potential lingual nerve damage
3. Increased need for repositioning |
1. Difficult to select proper size
2. Less flexibility in positioning
3. Not for use in abnormal or distorted upper airway anatomy
|
Desirable features of any supraglottic airway
Only those devices currently used
in clinical practice in both the United Kingdom and the United
States, with the exception of the Streamlined Liner of the
Pharynx Airway, will be discussed in
this chapter. See Chapter 21 and 25 for an
extensive review of the LMA and Combitube.
|
