Module 14
Advanced Airway Techniques
Part 2 - New Generation Supraglottic Ventilatory Devices
Desirable Features and Optimal Methods for Testing
DESIRABLE FEATURES OF SUPRAGLOTTIC AIRWAYS
There are certain questions that
influence the anesthesiologist’s choice of an airway for an
individual patient. For instance, does the anesthesiologist use
a single-use device, a device that can be reused most often, the
cheapest device, or the device that causes least trauma?
Do all devices maintain the airway reliably? Do any of
them protect the airway from regurgitation and pulmonary
aspiration? Which devices enable safe and effective
positive pressure ventilation? Will the device enable
access to the airway if required? Other questions relate
to how well these devices function in large cohorts. Are
there differences in ease of insertion and airway seal pressure
between the various devices? How often are manipulations
needed to maintain a clear airway during anesthesia? Which
devices are tolerated best during emergence? What are the
relative incidences of airway trauma and postoperative
pharyngolaryngeal morbidity? Unfortunately, in the
majority of cases, remarkably few data are available. The
manner in which new medical devices are regulated contributes to
this.
The desirable features of an
ideal supraglottic device relate to efficacy, versatility,
safety, reusability and cost. Manufacturing a quality product
is important. The device should be made of good quality
non-harmful materials. A long shelf life is desirable. Devices
designed to be reusable should be robust enough to allow
multiple uses without deterioration of performance. Similarly,
design should enable appropriate cleaning without damage or
deterioration. Most of these factors are overseen during the
statutory evaluations. Desirable features may be viewed from
the patient’s or anesthesiologist’s perspective.
The anesthesiologist wants a
device that is inserted reliably on the first attempt, producing
a clear airway for both spontaneous and controlled ventilation.
It must enable the anesthesiologist to maintain hands-free
anesthesia. Emergence should be without complications. The
incidence of airway trauma and post-operative sore throat should
be acceptably low. Design features or clinical evidence of
protection against aspiration is desirable, as is the ability to
access the trachea through the device. From the patient’s
perspective, the ideal device should not cause intraoperative
complications, device-associated trauma, or pharyngolaryngeal
morbidity. Let’s first consider the anesthesiologist’s
requirements.
The device should enable
insertion with minimal mouth opening (most require 2-3 cm mouth
opening) and with a light depth of anesthesia (the dose range
for different airways varies approximately two-fold).
Supraglottic devices requiring muscle relaxant for insertion are
of limited use.
All supraglottic airway devices
may cause airway obstruction from epiglottic downfolding. This
is reduced by ensuring correct insertion technique and by
designing devices with a slim leading edge. The slim profile of
the deflated LT and the deflation device and tip flattener that
are provided with the cLMA and pLMA are examples of such
design. The epiglottis may also cause obstruction by entering
the orifice of the airway device and a variety of design
features are aimed at avoiding this. These include epiglottic
bars (cLMA and FLMA), a large orifice too big to obstruct
(pLMA), multiple holes (combitube, Laryngeal Tube™), and a
hooded orifice with protective fins (PAx).
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