Contents:
Volume 1, Nomber 2; Jan, 2003 |
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Role
of Laryngeal Mask Airway in First Aids
in Confined Space
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Tzong-Luen Wang, MD, PhD, Kuo-Chih Chen, MD, Hsueh-Ju
Teng, MD, and Hang Chang, MD, PhD |
From the Department of Emergency Medicine(Wang
TL, Chen KC, Teng HJ, Chang H), Shin-Kong Wu Ho-Su Memorial Hospital.
Correspondence to Dr. Hang Chang, Department
of Emergency Medicine, Shin-Kong Wu Ho-Su Memorial Hospital, 95
Wen Chang Road, Taipei, Taiwan. E-mail M001043@ms.skh.org.tw
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Abstract
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Laryngeal mask airway (LMA) has
been shown to be an alterative method of definite airway but its
role in rescue from confined space has not been determined. One
hundred and sixty seven persons who attended the training course
of disaster medicine were enrolled as the study population. Sixty
two of them were men whereas the other 105 women. Thirty four of
the study population were medical doctors, 95 nurses, 30 emergency
medical technicians, and 8 laypersons. We arranged a workshop of
confined space medicine. The comparison of applicability between
conventional endotracheal intubation and LMA was made. Before evaluation,
every participant accepted detailed illustration and demonstration
of the skills. Every one was asked to perform airway management
for the manikins in confined space with face down, sitting position,
side position and “reverse” supine position. The success rate and
the time elapse for both endotracheal intubation and LMA application/intubation
was compared. Success rate of first LMA application is 100% for
all positions which is significantly better than those of endotracheal
intubation (85% for sitting position, P<0.01; 80% for side position,
P<0.01; 76% for face down, P<0.01; and 74% for “reverse” supine
position, P<0.001). The time elapse for first LMA application
was also significantly lower than those of endotracheal intubation
(as presented). The success rate and time elapse of first LMA intubation
and the number of trials before success was comparable to endotracheal
intubation. LMA was preferred as a choice of airway management in
confined space rescue. (Ann Disaster Med. 2003;1:85-96)
Key words: Laryngeal Mask Airway; Confined Space; First Aid; Disaster
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Introduction
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Although there have been many advances
in first aids in recent decades, the rescue in confined space still
remained a great challenge. For example, it may be difficult for
the rescue team or disaster medical assistant team (DMAT) to maintain
airway in a narrow space with no good preparation. The laryngeal
mask airway (LMA) may be a resolution under such circumstances.
The LMA was designed in the 1980’s and has gained widespread popularity
in clinical use in the last decade. 1,2
It allows either spontaneous or positive-pressure ventilation. With
advances in the design, it has also received more attention as a
tool for management of the difficult airway. 3-5
Because the placement of this device is less technique-dependent,
the learning curve will be adequate. 6-10
In other words, the LMA has theoretical basis for the rescue team
or DMAT to learn and use under difficult situations. 10-14
We then underwent the following study to compare the efficiencies
between traditional intubation and the LMA with or without intubation
in the confined space. |
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Methods |
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Study population |
One hundred and sixty seven persons
who attended the training course of disaster medicine in 2001 were
enrolled as the study population. Sixty two of them were men whereas
the other 105 women. Thirty four of the study population were medical
doctors, 95 nurses, 30 emergency medical technicians, and 8 laypersons.
According to the education background, 147 of them (88%) have ever
qualified as the basic life science providers, 70 (42%) as the providers
of advanced cardiovascular life support, and 55 of them (12%) were
neither. We therein classified the students into 4 classes according
to their self-determination in performance of intubation: Class
A (n=30), those who had good clinical experiences in intubation;
Class B (n=18) who ever completed the training of intubation but
had only limited clinical experiences; Class C (n=99) who had ever
attended the training course of intubation with no real performance;
and Class D (n=55) that had never been trained. |
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Study protocol |
We arranged a workshop of confined space medicine to
compare the applicability between conventional endotracheal intubation
and LMA with and without intubation. Before evaluation, every participant
accepted detailed illustration and demonstration of the skills. Every
one was asked to perform airway management for the manikins in confined
space with the following four positions: face down, sitting position,
side position and “reverse” supine position. The students would be
asked to re-prepare and intubate if initial attempts failed. The success
rate and the time elapse for both endotracheal intubation and LMA
application/intubation was compared. |
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Statistic Analysis |
The categorical data were inputted in Microsoft Excel
2000 for descriptive statistics and further qualitative analysis.
These results were analyzed using the chi-squared test. ANOVA with
a Newman-Keuls post hoc test was used to determine whether any significant
differences existed among continuous data. A P<0.05 was considered
to be statistically significant. |
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Results |
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For all positions, the success
rate of first LMA application is 100% and significantly better than
those of endotracheal intubation (85% for sitting position, P<0.01;
80% for side position, P<0.01; 76% for face down, P<0.01;
and 74% for “reverse” supine position, P<0.001) (Figure 1 ).
The time elapse for first successful LMA application was also significantly
lower than those of endotracheal intubation (Figure 2A ).
The success rate of first LMA intubation was comparable to that
of endotracheal intubation (88% vs. 85% for sitting position, P=NS;
80% vs. 80% for side position, P=NS; 78% vs. 76% for face down,
P=NS; and 76% vs. 74% for “reverse” supine position, P=NS) (Figure
3 ),
as was the time elapse between two comparisons (Figure 2B ).
The number of trials before successful application of endotracheal
tube was also comparable between two methods (data not shown).
To elucidate the possible effects of past experiences, we analyzed
the learning results according to the classification described above.
There were no differences in applying LMA and LMA intubation among
4 groups of different past experiences (for example, 88% for Class
A, 84% for Class B, 85% for Class C, and 72% for Class D in LMA
intubation, Figure 4A and
4B )
whereas there were significant differences for conventional intubation
(96% for Class A, 80% for Class 64% for Class C, and 30% for Class
D in LMA intubation, P<0.001 among 4 groups) (Figure 4C ).
The similar findings were also observed according to the performance
among different medical background. In other words, the success
rate were not significantly different in applying LMA or LMA intubation
no matter the students were physicians, nurses, emergency medical
technicians, or laypersons (Figure. 5 ). |
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Figure 1. The comparisons in success rate of first
LMA application and conventional intubation |
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Figure 2. The comparisons in time relapse between
LMA application and conventional intubation (A) and LMA intubation
and conventional intubation (B) |
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Figure 3. The comparisons in success rate of first
LMA intubation and conventional intubation |
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Figure 4. The comparisons in success rate of LMA
application, LMA intubation and conventional intubation in groups
of different experiences |
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Figure 5. The comparisons in success rate of LMA
application, LMA intubation and conventional intubation in groups
of different medical backgrounds |
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Discussion |
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In prehospital situations, the
LMA and the Combitube dual-lumen tube are both time-saving procedure
for maintaining patent airways. 9,10,15-17
However, in one study comparing the LMA and the Combitube for inexperienced
operators, the rate of successful LMA placements in anesthesized
and paralyzed patients was 100%, but the success rate only 92% with
a Combitube. 10 More complicated procedures
may contribute to the failure of the Combitube. In addition, the
Combitube cannot be used in patients with a protective reflex or
in pediatric victims, whereas the LMA has no such limitations. 18
Another study 7 showed that physicians-in-training
could insert an LMA successfully in 90% of victims with cardiopulmonary
arrest even when they hadn’t had any clinical experience using an
LMA.
The above observations have been again proven in our investigations.
The success rate of LMA application was almost 100% for every student,
independent of their education background and experiences. Evidence
from some preliminary studies (including our data) revealed that
the application of the LMA is not affected by the patient position, 19
past experience, 7-9 consciousness level, 1-4
or cervical immobilization. 21-23
These characteristics make the LMA more attractive in rescue of
victims in confined spaces. Our data revealed that the success rate
of first LMA application was 100% for various patient positions,
which is significantly better than the rates for endotracheal intubation
(85% for the sitting position; 80% for side position; 76% for face
down; and 74% for “reverse” supine position). The time elapsed for
first LMA application was also significantly lower than that for
endotracheal intubation. The success rate and time elapsed for first
ILMA and the number of trials before success was comparable to endotracheal
intubation. The advantages of LMA over conventional intubation in
different positions have demonstrated that the pre-shaped design
in LMA has overcome many clinical difficulties in using laryngoscope
and preparations.
However, the success of LMA rescue in the clinical settings still
depends on several factors such as the operator’s experience, clinical
pathways in airway management, and understanding of the interaction
between LMA insertion and cricoid pressure. 6
Surveys have demonstrated that the success rates in emergency rescue
are probably lower overall due to lack of familiarity with the device. 7-10
The overall LMA insertion success rate was 81% in 233 cases
in an Australian prehospital study. 11
Japanese paramedics’ experiences also showed overall excellent outcomes. 12
Brimacombe et al. 13,14 therein
suggested an algorithm for use of the LMA in failed intubation of
the nonfasting patient. |
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LMA as a Conduit Passage |
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Although the ILMA may be not the
first priority for most pre-hospital and confined space rescues,
it is still worthwhile to understand the LMA’s role as a conduit
for passing an endotracheal tube. A newly designed ILMA was specifically
designed for intubation. The trachea may thus be intubated blindly
through a properly placed LMA. 24 However,
success rates vary, depending on the operator’s experience, 25
technique, number of attempts, and equipment 26,27
according to others’ reports. With the advances in design modification,
the LMA may be used as a guide for a thin flexible airway stent
such as an elastic bougie or an intubating stylet for the passage
of an endotracheal tube. 13,28-30
Retrograde tracheal intubation over a catheter through an LMA has
also been reported. 31-36 Because of
technical difficulty in fibroptic intubation and retrograde tracheal
intubation for emergency physicians and being impractical in clinical
use, the usefulness in disaster medicine should be underscored. |
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Limitations of LMA |
The primary concern with LMA use
by emergency physicians and paramedics is incomplete protection
of the airway. There is a risk of aspiration in prehospital use
of the LMA because the device does not separate the trachea and
esophagus completely. 37-38 The Sellick
maneuver should be maintained continuously for high-risk patients,
such as those who have had bag ventilation and those in a non-fasting
state, in late pregnancy, with morbid obesity, or with upper gastrointestinal
hemorrhage. Although these were conflicting results in some reports, 39,40
Brimacombe’s meta-analysis 41 found
an incidence of 2 aspirations in 10,000 patients. We still need
to elucidate is whether aspiration is more commonly encountered
in the emergency department and prehospital situations because of
inadequate preparation.
Another problem is the use of the LMA in patients with either increased
airway resistance or very low lung compliance. 18
Inadequate ventilation due to air leakage and gastric distension
are predictable in attempting positive ventilation in “tight” asthmatics.
The LMA, as in conventional intubation, may induce reflex bronchospasm.
However, the severity is always less because the diameter of the
LMA is larger and because the LMA does not pass through the trachea. 18,42
Patients already in bronchospasm need to be monitored carefully. 43
Other complications resulting from LMA use are local irritation
causing coughing and bucking, upper airway injuries, pressure-induced
lesions (such as twelfth cranial nerve palsy), and sometimes hemodynamic
compromise. 44,45 Among them, pressure-induced
injuries may be related to an over-inflated cuff which causes mucosal
ischemia with subsequent injury. 46-48
Adequate cuff pressure and proper insertion technique are the primary
prevention strategies. |
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Conclusion |
The success rate and time elapse
of LMA application and first LMA intubation and the number of trials
before success were comparable to endotracheal intubation. LMA and
its intubation were preferred as a choice of airway management in
confined space rescue. |
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