Edward T. Crosby, MD
Ottawa Hospital - General Site and University of Ottawa
Objectives:
Comprehension
By the end of the Workshop, the participant should be able to derive a structured response to a difficult airway event and determine how new technologies may be applied.Operational
By the end of the workshop, the participant will have developed initial skills and insights into the application of the lighted stylet, laryngeal mask airway, Combitube™, Bullard™ laryngscope, and transtracheal airway kits in the management of the difficult airway.
1. The Difficult Airway - Definition of Terms
The ASA Task Force defined a difficult airway as "The clinical situation in
which a conventionally trained anesthesiologist experiences difficulty with mask
ventilation, difficulty with tracheal intubation, or both."1 The Task
Force further noted that the "difficult airway represented a complex interaction
between patient factors, the clinical setting, and the skills and preferences of the
practitioner".
The process of tracheal intubation can be divided into a number of element acts. Generally speaking, mask ventilation precedes laryngoscopy which is, in turn, followed by endotracheal intubation. Each of these element acts may be reviewed and difficulties related to them elucidated and defined. Successful mask ventilation would imply the ability to adequately ventilate and oxygenate a patient using a mask, circuit and supply of oxygen. The ASA task force defined difficult mask ventilation as occurring when:
Successful laryngoscopy would imply that an adequate view of the glottic structures and
laryngeal inlet to allow for tracheal intubation could be achieved using a direct
laryngoscope. Difficult laryngoscopy was defined by the ASA Task Force as
occurring when " It is not possible to visualize any portion of the vocal cords
with conventional laryngoscopy." In most instances, this would equate to the
Grade IV laryngoscopy designation of Cormack and Lehane. The ASA Task Force defined difficult
endotracheal intubation as occurring when "proper insertion of the
tracheal tube with conventional laryngoscopy requires more than three attempts or more
than 10 minutes".
2. The Difficult Airway - Incidence
The incidence of the difficult airway, difficult laryngoscopy and difficult intubation
are not well defined. Rocke reported that some difficulty was experienced during
intubation in 7.9% (119/1500) of parturients undergoing general anesthesia for cesarean
section.3 2% of the patients (30/1500) were deemed to be very difficult to
intubate. In a nonobstetrical, mixed surgical population, Rose noted that 2.5% of patients
required two laryngoscopies to achieve tracheal intubation and that 1.8% required more
than three.2 This data, if an accurate reflection, suggests that some degree of
difficulty with intubation is experienced more frequently during obstetrical anesthesia
than general surgical anesthesia (7.9% versus 2.5%) but that very difficult intubations
are seen with a similar frequency in obstetrical and nonobstetrical surgical populations
(2% versus 1.8%). The incidence of difficult mask ventilation is again not well defined
but appears to be much less than that of difficult intubation. In a non-obstetrical
population, Rose reported an incidence of 0.01% whereas Benumoff cited an incidence of
0.0001-0.02%, although neither the source nor the patient populations for the latter
quoted incidence were reported.2,4
3. Preoperative Assessment of the Airway - Prediction of Difficult Intubation
Mallampati reported a correlation between the visibility of oropharyngeal structures and the degree of difficulty of laryngeal exposure during laryngoscopy and concluded that difficult laryngeal visualization could be predicted in most cases by assessing the visibility of the faucial pillars and uvula.5 Preoperative oropharyngeal examination and classification using a three tier (class I = soft palate, pillars and uvula visualized; class II = soft palate and pillars visualized; class III = soft palate visualized) grading system was proposed. Prospective application of the system by Mallampati revealed that in the majority of patients with poor visualization of pharyngeal structures, laryngoscopy was difficult. Samsoon and Young reviewed a series of obstetrical and general surgical patients who were known difficult intubations and assigned Mallampati classifications.6 They added a further tier (class IV = no pharyngeal structures visualized) to the Mallampati grading scheme. Samsoon observed that among patients in whom laryngoscopy was known to be difficult, class III and class IV assignments predominated. The Mallampati classification system was further evaluated by Tham who studied the effects of posture, phonation and observer on Mallampati classification.7 Phonation produced a marked improvement of view and a more favorable classification whereas the supine position resulted in a somewhat worse view and a higher grade assignment. Wilson developed a five factor evaluation mechanism after reviewing the features of patients who had proven to be difficult to intubate.8 Patient weight, head and neck movement, jaw movement, mandibular size and prominence of the upper incisors were each graded (0-2) and a rank sum score was determined. Of the five factors identified by multivariate analysis as contributing to difficult intubation, obesity was the weakest predictor.
Rocke reported the factors, assessed preoperatively, that were associated with
difficult intubation in 1500 parturients undergoing emergency and elective cesarean
section under general anesthesia.3 He utilized prospective application of the
Samsoon-Young modified Mallampati classification for airway assessment as well noting the
presence of the following maternal characteristics: short neck; obesity; missing maxillary
incisors; protruding maxillary incisors; single maxillary tooth; receding mandible; facial
edema; and swollen tongue. An easy, first attempt intubation occurred in 96% of class I
airways, 91% of class II, 82% of class III and 76% of class IV airways. Although
difficulty with intubation increased with increasing airway class, most patients with
class IV airways were not difficult to intubate. Only 4-6% of class III and IV airways,
respectively, were considered to be very difficult intubations. There were two failed
intubations (1/750), one each in class II (0.2%) and class III (0.3%). Rocke speculated on
the possibility that a class IV assignment in the obstetrical patients has a different
significance than a similar determination in a non-obstetric patient, given that so few of
the class IV patients proved to be difficult intubations. After using univariate and
stepwise multiple logistic regression analysis to eliminate associated factors, the
following emerged as etiologic factors (relative risk in brackets) predicting difficult or
failed intubated: airway class II (3.23); airway class III (7.58); airway class IV
(11.30); short neck (5.01); receding mandible (9.71); and protruding maxillary incisors
(8.0) Obesity and a short neck were linked factors, with obesity being eliminated as a
risk factor if short neck were excluded.
All patients being considered for an anesthetic, whether regional or general, should
undergo airway evaluation and have a Mallampati-Samsoon classification assigned. Davies
encourages evaluation of the airway in the supine position although Tham has reported that
there is little difference in designated class with supine versus upright position.7,10
In fact, based on Tham's data, routine assessment in the supine position would result in
decreased specificity of the Mallampati assessment. Using the upright posture and
phonation to obtain the best Mallampati grade is likely to reflect more
accurately the best laryngoscopic view obtainable and may reduce the incidence of
false positive assessments. Further airway evaluation should include determination of the
patient's body habitus, mouth opening (interdental distance), prominence of upper
incisors, ability to protrude the lower jaw beyond the upper incisors, mandibular length,
thyromental distance and neck extension. The latter assessment may be carried out with an
simple bedside manoeuvre.11 The distance from the sternal notch to the tip of
the chin is measured with the patient both in the neutral and maximally extended position.
With extension the distance should increase. An increase of less than 5 cm is associated
with a high sensitivity, specificity and positive predictive value for difficult
laryngoscopy. An increase of greater than 5 cm should reassure the examiner that neck
mobility is normal. After airway assessment, a summary conclusion should be generated as
to the anticipated difficulty in performing laryngoscopy and the patient can be advised of
the both the conclusion and its implications. However, most authorities, who have reviewed
the use of the different assessment techniques to predict difficult intubation, conclude
that the simple and practical strategies have a high sensitivity but low specificity and
low positive predictive value with respect to the diagnosis. Though efforts to perform
routine airway assessments are to be encouraged, it must be recognized that many
difficulties will not be predicted even on the basis of the most diligent of assessments
and strategies to manage the unexpected difficulties should be performulated and
practised.
4. The Difficult Airway - Management Strategies
Once a difficult airway situation has been diagnosed, its nature must be elucidated. If
mask ventilation is difficult or tenuous, addressing it is the priority; effective
oxygenation must be ensured rapidly. If mask ventilation is easily achieved, but the
patient is at risk of aspiration, airway protection with cricoid pressure and patient
positioning should be sought while the decision as to how to proceed is made. Finally, if
ventilation is easy in an otherwise not at risk patient, alternative strategies can be
considered to achieve intubation.
5. New Technologies - Application in the Difficult Airway
New novel technologies and adapted older technologies directed towards the management
of the difficult airway continue to proliferate. Although their specific roles in the
difficult airway drill have not been formally studied in all cases, some conclusions may
be drawn from the experience accumulated to date with them.
5.1 Difficult Mask Ventilation
In rare cases, it is impossible either to ventilate the lungs of a patient via mask or
to intubate the trachea. Obviously the compelling clinical imperatives in the setting of
difficult or failed mask ventilation are the establishment of a patent airway and ensuring
patient oxygenation. Under these circumstances, unless there is an alternative ventilation
method immediately available, death will rapidly ensue. Alternative technologies aimed at
achieving endotracheal intubation are only applicable in this situation if they can
rapidly achieve a patent airway. Otherwise the goal of intubation is clearly secondary to
that of ventilation. Technologies intuitively useful in this setting are the laryngeal
mask airway and the esophageal tracheal Combitube.
5.1A The Role Of The Laryngeal Mask Airway
The laryngeal mask airway (LMA) is a novel device recently introduced into anesthetic
practice.12 The LMA is inserted blindly into the pharynx and forms a low
pressure seal around the laryngeal inlet. It is easily placed and a clear, unobstructed
airway may be obtained in virtually all patients, even when used by physicians with little
or no prior experience.13 Insertion of the LMA is not more difficult in
patients with class III or IV airways or in those patients in whom laryngoscopy reveals
grades 3 or 4 views.14 The airway is occasionally completely or partially
obstructed after placement of the LMA and this is usually related to downfolding of the
epiglottis or infolding of the aryepiglotic folds.15 The most outstanding
feature of the LMA is its ability to rapidly provide a clear airway and there are now
numerous reports of the LMA relieving hypoxia after failed intubation and ventilation.16-21
It has also been utilized in parturients who could not be intubated but whose airways
could be managed with face mask anesthesia.21,22 This latter application has
generated much controversy for two reasons, in particular. First, there is evidence that
the LMA is more likely to promote gastric regurgitation when compared to face mask
anesthesia.24,25 The LMA results in a decrease in the LES barrier pressure in
anesthetized, spontaneously breathing patients compared with a face mask which promotes an
increase in barrier pressure. The postulated mechanism is that the LMA causes reflex
relaxation of the LES by distention of the hypopharyngeal muscles, similar to the effect
of a food bolus. Although El Mikatti did not find an increased incidence of regurgitation
in patients managed with an LMA compared with facemask anesthesia, it was commented that
two LMA patients not included in the study analysis had signs of regurgitation after
vigorous coughing during light anesthesia.26 There were no similar events in
the patients managed with a facemask. Second, it has been suggested that the inflated cuff
of the LMA may prevent escape of regurgitated material into the pharynx and deflect it
instead into the airway.27 This effect would diminish or negate the protective
effect of the left lateral position during a failed intubation drill.
When the patients' lungs can be ventilated adequately with a face mask after failed
intubation, the LMA confers no advantage and may in fact promote gastric regurgitation.
The liberal use of a LMA in this scenario has been discouraged.28 The airway
should be maintained with a face mask and cricoid pressure and spontaneous ventilation
should be allowed to resume. Once spontaneous ventilation has returned through an open
airway, there again would be little advantage to be gained by passing a LMA.29
When adequate ventilation cannot be maintained after failed intubation, the LMA could be
tried. An attempt to pass it should be made early in the course of management after it has
been determined that intubation is impossible and ventilation is difficult or impossible
with the face mask. The laryngeal reflexes are likely to still be blunted by the residual
effects of the anesthetic induction and the patient is less likely to respond unfavourably
to airway placement if it is attempted early.13 The stimulation related to
passage of a laryngeal mask is approximately the same as that for an oropharyngeal airway.30
Because there should be less gastric distention if there has not been persistent and
forceful attempts to ventilate a patient with an obstructed airway, the risk of
regurgitation may be reduced.
Whether or not cricoid pressure should be released during insertion of the LMA is
controversial but it is reasonable and prudent to do so for brief periods to assess the
result on laryngoscopy, intubation and ventilation. The presence of the LMA does not
appear to compromise effective application of cricoid pressure although cricoid pressure
makes the successful insertion of the LMA more difficult.31-34 Once the LMA is
placed, ventilation is also more difficult with maintained cricoid pressure. It is also
more difficult to pass an endotracheal tube through the LMA and into the trachea, both
blindly and assisted by a fiberoptic scope, with cricoid pressure applied.31,32
Cricoid pressure causes an anterior tilt to the larynx and this is likely the cause of
the difficulty intubating the trachea.35 The anterior angulation of the larynx
may also result in closure of the vocal cords and airway obstruction and, although this
has been reported, it is presumably rare.36 The LMA is not an alternative to
the endo-tracheal tube but rather, it should be considered an alternative to the face mask
when it is not possible to ventilate and oxygenate a patient through a face mask after
failed intubation.37 After this determination has been made, an attempt to pass
the LMA should be made early, with cricoid pressure maintained. If it is not possible to
pass the LMA with cricoid pressure maintained, the pressure should be briefly released, a
second pass made and the cricoid pressure reapplied. Again, if it is not possible to
establish an open airway, the LMA should be removed and the face mask reapplied with
cricoid pressure now released. An attempt to ventilate the patient without cricoid
pressure can now be made and consideration should now be given to the use of either a
CombitubeTM or surgical airway depending upon the success achieved with the
face mask and the obstetrical circumstances.
If ventilation is re-established with the LMA, the patient should be allowed to awaken.
The option to wake the patient should only be excluded by a well recognized urgency to
proceed for patient welfare. In this circumstance, general anesthesia may be provided via
the LMA, with cricoid pressure maintained if necessary to protect the airway. Other
factors, such as the patient's preoperative reluctance to undergo surgery with regional
anesthesia should in no way compel the anesthesiologist to carry on with general
anesthesia with a controlled but unpro-tected airway. Once the airway has been opened with
the LMA and the decision made to proceed with general anesthesia further steps may be
taken to protect the airway if indicated by circumstance or surgical requirement.
Intubation through the LMA with a small gauge (6.0 mm) endotracheal tube, both blind or
assisted with a bougie, tube changer or fiberoptic scope have all been described.18,31,38,39
Clearly, if not readily successful, attempts to pass an endotracheal tube should not be
persistent, given that an adequate airway has already been established withan LMA.
If it is not possible to open the airway with the LMA, consideration should be given to
the use of the CombitubeTM, transtracheal oxygenation or the creation of a
surgical airway. Recent published commentary supports the use of the LMA prior to creation
of a surgical airway in the cannot-intubate, cannot-ventilate situation.40,41
5.1B The Role of the CombitubeTM
The CombitubeTM (© Kendall Health Care Products Company, Mansfield, MA) is
a new emergency airway, which can be used in the esophageal as well as tracheal positions.42-44
It is a double lumen tube, combining the function of an esophageal obturator airway
and a con-ventional endotracheal airway. The esophageal lumen has an open upper end,
perforations at the pharyngeal level and a closed distal end. The tracheal lumen has open
proximal and distal ends. The lumens are separated by a partitioning wall and each is
linked, via a short tube with a connector. An oropharyngeal balloon is situated proximal
to the pharyngeal perforations and it serves to seal the oral and nasal cavities after
insertion. At the lower end, a second cuff serves to seal either the trachea or
oesophagus. To place the tube, the lower jaw and tongue are lifted and the tube is
inserted until the printed ringmarks lie between the teeth or alveolar ridges. The
oropharyngeal balloon is inflated with 100 ml of air and the distal balloon with 10-15 ml
of air. There is an expectation of esophageal placement with blind insertion and
ventilation begins through the esophageal lumen. Auscultation of breath sounds over the
chest and confirmation of expired carbon dioxide confirms ventilation. In the event of
negative auscultation over the lungs, the CombitubeTM has been placed in the
trachea and ventilation is carried out through the tracheal lumen.
Although experience with the CombitubeTM is limited to date (Appendix 1), it
is clearly an alternative to the LMA in the patient in whom intubation has failed and
ventilation is difficult. It can be placed quickly and allows for protection of the airway
thus preventing aspiration. It probably offers a greater degree of airway protection than
does the laryngeal mask airway, although the two have not been formally compared.45,46
The stomach can be evacuated, usually through the tracheal lumen. Cricoid pressure would
have to be released transiently to allow for placement of the CombitubeTM and
the airway would be at risk from aspiration during the brief period before cuff inflation.
The CombitubeTM has evolved from the esophageal obturator and esophageal
gastric airways. Both had been criticized because of difficulty in obtaining effective
ventilation, the potential for esophageal trauma on insertion, aspiration on removal and
inadvertent tracheal placement resulting in total airway obstruction.
Although the ASA difficult airway algorithm presently lists the laryngeal mask airway
and the Combitube, along with TTJV, as appropriate nonsurgical solutions for the
cannot-ventilate-cannot-intubate situation, they both deserve higher prominence and
ranking in the minds of many anesthesiologists for the following four reasons. First, they
will likely work as ventilatory mechanisms. Second, they both can be inserted blindly,
quickly, and with a relatively low level of skill. Third, so far they have been associated
with few complications. Fourth, although TTJV is also rapidly instituted with a low level
of skill and will very likely work well if the practitioner has prepared in advance, there
is still a significant risk of barotrauma (too large tidal volume, too short exhalation,
letting go of the catheter with subsequent dislodgment). TTJV is not without its risks and
it should not be engaged upon by practitioners inexperienced in its application. Other
transtracheal techniques such as retrograde catheter techniques and percutaneous
cricothyrotomy probably should be similarly restricted in their use to very compelling
clinical situations.
5.2 Difficult Intubation
New technologies are obviously useful for difficult intubation in the setting of poor
laryngoscopic view but adequate mask ventilation. Obviously, best laryngoscopic view is
dependent on optimal positioning of the patient, an experienced practitioner with capable
assistance and a technique designed to ensure that the best view is obtained. Berumof's
description of optimal external laryngeal manipulation (OELM) represents a practical model
of such a technique.47 The patient should be in a sniff position (slight
flexion of the neck on the head and severe extension of the head on the neck), which
aligns the oral, pharyngeal, and laryngeal axis into more of a straight line. In some
patients (such as the obese) obtaining an optimal sniff position may require placing
pillows and blankets under the scapula, shoulders, nape of the neck, and head. If the
laryngoscopic grade is either II (just arytenoids), III (just epiglottis), or IV (just
soft palate), then OELM should be used. OELM very frequently can improve the
laryngoscopic view by at least one whole grade and should be an inherent part of
laryngoscopy and an instinctive and reflex response to a poor laryngoscopic view. The
proper function of both the Macintosh and Miller blades is dependent on using an
appropriate length of blade. In order to lift the epiglottis out of the line of sight, the
Macintosh blade must be long enough to put tension on the glossoepiglottic ligament, and
the Miller blade must be long enough to trap the epiglottis against the tongue. Thus, in
some patients it may be appropriate to change the length of the blade one time in order to
obtain proper blade function. In some patients a Macintosh blade may provide a superior
view or intubating conditions than a Miller blade, and vice versa. A Macintosh blade is
generally regarded as a better blade whenever there is little upper airway room to pass
the endotracheal tube (e.g., small narrow mouth, palate, oropharyrix), and a Miller blade
is generally regarded as a better blade in patients who have a small mandibular space
(anterior larynx), large incisors, or a long, floppy epiglottis.
Once it has been determined that optimization of laryngoscopy still results in a poor
or inadequate view, early consideration should be given to abandoning direct laryngoscopy
in favour of an alternative technique. Persistence with direct laryngoscopy for multiple
attempts is associated with undue morbidity and occasional mortality.2
Well-described and confirmed useful alternatives to direct laryngoscopy are many and are
currently underutilised. Lighted stylet (Laerdal's Trachlight )
facilitated intubation is easily learned and has a high success rate in rapidly achieving
endotracheal intubation even when applied to subpopulations that have failed conventional
laryngoscopic intubation.48 Its effectiveness may be reduced in very obese
patients or in those in whom cricoid pressure is required as transilluminated light is
diminished. The laryngeal mask airway is useful in this setting, most particularly due to
its well described use as an adjunct to intubation, both in awake patients and under
anaesthesia, in settings of failed or difficult intubation. Finally, the application of
fibreoptic techniques to the difficult to intubate patient are well described and flexible
fibreoptic facilitated intubation represent is likely one of the most commonly described
alternative techniques employed in difficult intubation. Rigid fiberoptic laryngoscopes
such as the Bullard laryngoscope are relatively underutilised in this
setting, yet represent ideal alternatives to flexible fibreoptic laryngoscopy. Because of
its rigid structure, the Bullard scope is able to achieve its own endoscopic
"airspace" to allow for anatomic visualization. Similar to flexible fibreoptic
scopes, the Bullard may be readily set up if it is immediately available. Oxygen
insufflation is possible via its suction port and once visualization is achieved, the
endotracheal tube may be readily passed. All fibreoptic techniques require both training
and experience. Unfortunately, training in the Bullard scope is woefully inadequate in
most training institutions.
Benumof describes three general situations in which an anesthesiologist will be
required to intubate the trachea of an unconscious or anesthetized patient whose airway is
difficult to manage.47 First, the patient may already be unconscious (e.g.,
posttrauma) or anesthetized (e.g. drug overdose). Second, the patient may absolutely
refuse or not tolerate awake intubation (e.g., a child, a mentally retarded patient, or an
intoxicated combative patient. Third, and perhaps most commonly, the anesthesiologist may
fail to recognize intubation difficulty on the preoperative evaluation. Of course, even in
the first and second situations above, the preoperative airway evaluation is very
important because the findings may dictate the choice of intubation technique. In all
three of the situations above, the patient may, in addition, have a full stomach. All of
the intubation techniques that are described for the awake patient can be used in the
unconscious or anesthetized patient without modification. However, direct and fiberoptic
laryngoscopy may be slightly more difficult in the paralyzed, anesthetized patient
compared to the awake patient because the larynx may become more anterior relative to
other structures due to relaxation of oral and pharyngeal muscles. In addition, and more
importantly, the upper airway structures may coalesce into a horizontal plane instead of
separating out in a vertical plane.
In the anesthetized patient whose trachea has proven to be difficult to intubate, it is
necessary to try to maintain gas exchange between intubation attempts by mask ventilation
and also during intubation attempts whenever possible. Additionally, it is extremely
important to realize that the amount of laryngeal edema and bleeding will very likely
increase after every forceful intubation. Although laryngeal edema and bleeding can occur
with any intubation method, it is most common after use of a laryngoscope or retraction
blade. Consequently, if there does not appear to be anything really new or different that
can be atraumatically and quickly tried (better sniff position, external laryngeal
manipulation, new blade, new technique, much more experienced laryngoscopist, etc.) after
a few failed intubation attempts, and ventilation by mask can still be maintained it is
prudent to cease attempting to intubate the trachea and to awaken the patient, continue
anesthesia via mask ventilation, or perform a transtracheal technique (tracheostomy,
cricothyrotomy or retrograde intubation) before the ability to ventilate
the lungs via mask is lost. In fact, the most common scenario in the respiratory
catastrophes in the ASA closed-claims study was the development of progressive difficulty
in ventilating via mask between persistent and prolonged failed intubation attempts; the
final result was inability to ventilate via mask and provide gas exchange.49 If
the surgical procedure is not urgent, awakening the patient and doing the procedure
another day will allow for better planning. Still, many other cases may be done (and may
have to be done) via mask ventilation if it is reasonably easy. Finally, in some cases,
the trachea will have to be intubated by tracheostomy or cricothyrotomy.
Summary
Theoretically, every anesthesiologist should be familiar with and well practiced in a
variety of the intubation techniques that are available so that when an airway problem
occurs, it can be managed with a solid armamentarium of information and experience.
However, with the rapid advancements in airway management technology, many of the newer
airway devices are foreign to most anesthesiologists. Rose has reported that alternatives
to direct laryngoscopy were used in only 1.9% of 18,558 tracheal intubations in a tertiary
care hospital.2 If awake fibreoptic laryngscopy was excluded, tracheal
intubations were achieved through direct laryngoscopy almost exclusively. Rose further
reported that, if Grade 3-4 laryngscopy was noted, 16% of patients experienced three or
more laryngscopies before tracheal intubation was achieved. This suggests that experienced
faculty will persevere with a technique even if it is obvious from the outset that it is
not optimal for the task at hand. Perhaps this is because many anesthesia care providers
lack the fundamental clinical skills necessary to implement many of the options presented
in the difficult airway algorithms.
Acquiring the equipment is generally not the problem: learning to use it is.
Self-teaching, through reading product information literature and clinical studies that
critically evaluate the equipment, viewing instructional videotapes, attending specialized
lectures and workshops, are a beginning, but each of these solutions has major limitations
or deficiencies. They do not substitute for hands-on experience. Learning to use the
equipment when an airway management problem presents itself is an extremely common
occurrence, but it is usually an unrewarding situation that impacts negatively on the
practitioner and the patient. Participating in specialized airway courses and workshops is
an excellent means of introducing the manual skills required to implement airway devices,
but practice in mannequins does not accurately simulate "real" patients and
therefore is often not directly applicable. Mannequins have wide open, patent channels
with immobile airway structures, which is markedly different from an actual airway.
References
Appendix 1.
The Application of the Combitube as an Initial Airway in Arrest Situations
Unpublished data on the use of the Combitube for airway management during cardiopulmonary arrest in Montérégie's (South Shore Montreal) EMS system was provided by Dr. Daniel Lefrançois, the medical coordinator of Emergency Medical Services for the system.
The EMS system serves a population of 1.3 million living in a 10,000 km2 mixed urban, suburban and rural environment. Care is provided by BLS-trained attendants with additional skills in automated external defibrillation (AED) and airway management using the Combitube. 400 EMT's respond to 60,000 calls annually, 1000 are for cardiorespiratory arrest.
The experience from November 1/92 to October 31/95 was reviewed and 1637 cases where the Combitube was available were identified. In 1445/1637 cases the Combitube was successfully installed. For 87/192 instances where Combitube was uninstalled, the patients had DNR orders (27), were spontaneously breathing after defibrillation (33), or no attempt was made to install the tube. (27) Two patients had obstructing foreign bodies, five had obstructing tumours of pharynx or larynx, two had an in-situ tracheotomy, one had esophageal stenosis, and 11 had severe airway deformations related to suicidal hanging. In 84 cases (~5.1%) there were failed placements without an apparent etiology to explain the failure. 1122 Combitube installations were evaluated; 1025 (91.3%) patients were adequately ventilated; 39 (3.5%) were being ventilated by the wrong conduit; 39 (3.5%) were inadequately evaluated and; 19 (1.7%) demonstrated inadequate ventilation. Traumatic complications, barotrauma, aspiration and technical failures were uncommon in the reviewed experience.
Lefrançois concluded that: 1) the Combitube may be used safely by BLS-skilled EMT's; and 2) that the Combitube provided adequate ventilation in majority of installations.