Upper Airway Obstruction
Upper Airway Obstruction
Upper Airway Obstruction
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Ch37 7/10/08 9:47 AM Page 388<br />
37<br />
<strong>Upper</strong> <strong>Airway</strong> <strong>Obstruction</strong><br />
José C. Yataco, MD<br />
Atul C. Mehta, MD<br />
Critical Care Pearls<br />
• <strong>Upper</strong> airway obstruction (UAO) is a life-threatening emergency that requires prompt<br />
diagnosis and treatment.<br />
• Severe UAO can be surprisingly asymptomatic at rest if it develops gradually. Sudden<br />
clinical deterioration is unpredictable.<br />
• Patients with possible UAO must never be sedated until the airway is secured. Minimal<br />
sedation may precipitate acute respiratory failure.<br />
• Achievement of airway patency in total airway obstruction and reestablishment of ventilatory<br />
airflow is the first and foremost goal of the treating physicians.<br />
• Critical care physicians must be aware that pharmacologic interventions (epinephrine,<br />
steroids, and heliox) provide temporary support but cannot significantly improve<br />
mechanical UAO.<br />
• Bronchoscopy constitutes the most accurate diagnostic tool and frequently provides the<br />
best way to correct UAO.<br />
• Cricothyroidotomy is the surgical intervention of choice to reestablish airflow when<br />
medical interventions have failed.<br />
<strong>Upper</strong> airway obstruction (UAO) is one of<br />
the most serious emergencies faced by<br />
critical care physicians. Early diagnosis followed<br />
by restoration of airflow is essential to<br />
prevent cardiac arrest or irreversible brain<br />
damage that occurs within minutes of complete<br />
airway obstruction (1,2).<br />
Although a long list of causes may be<br />
responsible for acute UAO, management must<br />
begin almost immediately after recognition of<br />
the problem. If there is an actual or potential<br />
obstruction sufficient to cause ventilatory or<br />
oxygenation impairment, an intervention to<br />
secure the airway is indicated by whatever<br />
388<br />
method appropriate at the time. No single<br />
method is suitable in all instances; selection<br />
depends on the assessment of the circumstances<br />
(1-3). The timing of the intervention,<br />
medical, or surgical, is determined based on<br />
the condition of the patient. In practice, an<br />
elective procedure before acute decompensation<br />
is always preferable.<br />
Etiology and Pathogenesis<br />
For purposes of this chapter, upper airway<br />
is considered to represent the conducting
Ch37 7/10/08 9:47 AM Page 389<br />
passages extending from the nose or mouth<br />
to the main carina (Figure 37-1).<br />
UAO may be functional or anatomic and<br />
may develop acutely or subacutely. Relapsing<br />
polychondritis constitutes a good example of<br />
functional UAO caused by lack of a firm cartilaginous<br />
structure to support the tracheal<br />
wall. Squamous cell carcinoma of the larynx<br />
represents an anatomic example of UAO.<br />
Narrowing of the upper respiratory tract<br />
has an exponential effect on airflow because<br />
Palatine tonsil<br />
Tongue<br />
Oral pharynx<br />
Retropharyngeal space<br />
Root of tongue<br />
Geniohyoid muscle<br />
Mylohyoid muscle<br />
Submandibular<br />
space<br />
Vallecula<br />
Epiglottis<br />
Hypophyarynx<br />
Vocal cord<br />
Thyroid cartilage<br />
Larynx<br />
Cricoid cartilage<br />
Trachea<br />
Sternum<br />
<strong>Upper</strong> <strong>Airway</strong> <strong>Obstruction</strong> 389<br />
linear airflow is a function of the fourth<br />
power of the radius (2-4). Although UAO<br />
occurs at any level of the upper respiratory<br />
tract, laryngeal obstruction has a particular<br />
importance because the larynx is the narrowest<br />
portion of the upper airway. The narrowest<br />
portion of the larynx is at the glottis in<br />
adults and the subglottis in infants (5).<br />
Some infections such as parapharyngeal<br />
or retropharyngeal abscesses and Ludwig<br />
angina (mixed infection of floor of the<br />
Figure 37-1 Anatomy of the upper airway. (Adapted from Aboussouan L, Stoller JK. Diagnosis<br />
and management of upper airway obstruction. Clin Chest Med. 1994;15:35-53; with permission.)
Ch37 7/10/08 9:47 AM Page 390<br />
390 Systemic Disorders<br />
mouth) can be associated with severe soft tissue<br />
swelling causing UAO.<br />
The differential diagnosis of UAO is wide<br />
and varies by age group and by clinical setting.<br />
Table 37-1 summarizes the most common<br />
causes of airway obstruction. Figures<br />
37-2 and 37-3 show examples of benign and<br />
malignant causes of UAO.<br />
Clinical Signs and Symptoms<br />
In a conscious patient, signs and symptoms of<br />
UAO include marked respiratory distress,<br />
altered voice, dysphagia, odynophagia, the<br />
hand-to-the-throat choking sign, stridor, facial<br />
swelling, prominence of neck veins, absence of<br />
air entry into the chest, and tachycardia. In an<br />
Table 37-1 Differential Diagnosis of <strong>Upper</strong><br />
<strong>Airway</strong> <strong>Obstruction</strong> According to Etiology<br />
Traumatic causes<br />
• Laryngeal stenosis<br />
• <strong>Airway</strong> burn<br />
• Acute laryngeal injury<br />
• Facial trauma (mandibular or maxillary fractures)<br />
• Hemorrhage<br />
Infections<br />
• Suppurative parotitis<br />
• Retropharyngeal abscess<br />
• Tonsillar hypertrophy<br />
• Ludwig’s angina<br />
• Epiglottitis<br />
• Laryngitis<br />
• Laryngotracheobronchitis (croup)<br />
• Diphtheria<br />
Iatrogenic causes<br />
• Tracheal stenosis post-tracheostomy<br />
• Tracheal stenosis post-intubation<br />
• Mucous ball from transtracheal catheter<br />
Foreign bodies<br />
Vocal cord paralysis<br />
Tumors<br />
• Laryngeal tumors (benign or malignant)<br />
• Laryngeal papillomatosis<br />
• Tracheal stenosis (caused by intrinsic or<br />
extrinsic tumors)<br />
Angioedema<br />
• Anaphylactic reactions<br />
• C1 inhibitor deficiency<br />
• Angiotensin-converting enzyme inhibitors<br />
Figure 37-2 Tracheal amyloidosis causing<br />
narrowing of the distal trachea.<br />
Figure 37-3 Extrinsic compression of the<br />
trachea caused by intrathoracic malignancy.<br />
unconscious or sedated patient, the first sign of<br />
airway obstruction may be inability to ventilate<br />
with a bag-valve mask after an attempt to open<br />
the airway with a jaw-thrust maneuver. After a<br />
few minutes of complete airway obstruction,<br />
asphyxiation progresses to cyanosis, bradycardia,<br />
hypotension, and irreversible cardiovascular<br />
collapse (1-3).<br />
Occasionally, UAO can develop slowly and is<br />
confused with reactive airway disease. However,
Ch37 7/10/08 9:47 AM Page 391<br />
the obstructive noise or stridor is thought to be<br />
a specific for UAO. Stridor is heard during the<br />
entire respiratory cycle but typically intensifies<br />
during inspiration and is usually more prominent<br />
above the neck. The presence of stridor<br />
indicates severe airway obstruction (airway passage<br />
Ch37 7/10/08 9:47 AM Page 392<br />
392 Systemic Disorders<br />
Airflow, L/S<br />
A<br />
Airflow, L/S<br />
C<br />
10<br />
5<br />
5<br />
10<br />
10<br />
5<br />
5<br />
10<br />
Expiration<br />
Inspiration<br />
100 0<br />
Lung volume, % VC<br />
Expiration<br />
Inspiration<br />
100 0<br />
Lung volume, % VC<br />
Airflow, L/S<br />
B<br />
Airflow, L/S<br />
D<br />
10<br />
5<br />
5<br />
10<br />
10<br />
5<br />
5<br />
10<br />
Expiration<br />
Inspiration<br />
100 0<br />
Lung volume, % VC<br />
Expiration<br />
Inspiration<br />
100 0<br />
Lung volume, % VC<br />
Figure 37-4 Flow-volume curves in upper airway obstruction. (A) indicates the normal contour of<br />
the inspiratory and expiratory curves; (B) With variable intrathoracic obstruction (e.g.,<br />
tracheomalacia within the thorax), obstruction is marked during exhalation with marked truncation<br />
of the expiratory curve; (C) With variable extrathoracic obstruction (e.g., collapse of tracheal cartilage<br />
in the neck following trauma), obstruction is more marked during inspiration; (D) Finally, with<br />
fixed obstructions (e.g., tracheal stenosis), both the inspiratory and expiratory curves are markedly<br />
truncated. (Adapted from Hall JB, Schmidt GA, Wood LD, eds. Principles of Critical Care. New York:<br />
McGraw-Hill; 1992; with permission.)<br />
subdiaphragmatic abdominal thrust can force<br />
air from the lungs; this may be sufficient to<br />
create an artificial cough and expel a foreign<br />
body from the airway. Repeat abdominal<br />
thrusts may be needed to clear the airway.<br />
Several medical and surgical approaches<br />
are available in the management of UAO<br />
including oropharyngeal airways, endotra-<br />
cheal intubation (transnasally or orally),<br />
tracheotomy, cricothyroidotomy, fiberoptic<br />
intubation, racemic epinephrine, corticosteroids,<br />
helium–oxygen mixtures, laser therapy,<br />
bronchoscopic dilation, and airway<br />
stenting (Table 37-2). The selection of the<br />
intervention will depend on the cause of UAO<br />
and the urgency to obtain a secure airway.
Ch37 7/10/08 9:47 AM Page 393<br />
Table 37-2 Interventions in <strong>Upper</strong> <strong>Airway</strong><br />
<strong>Obstruction</strong><br />
Medical Interventions<br />
Heimlich maneuver (suspected foreign body<br />
aspiration)<br />
Oropharyngeal airways<br />
Endotracheal intubation (transnasally or orally)<br />
Racemic epinephrine<br />
Corticosteroids<br />
Helium–oxygen mixture<br />
Surgical or Bronchoscopic Interventions<br />
Fiberoptic intubation<br />
Cricothyroidotomy<br />
Tracheostomy<br />
Laser/electrocautery/balloon dilation<br />
<strong>Airway</strong> stenting<br />
Racemic Epinephrine<br />
Racemic epinephrine is usually used in circumstances<br />
when the patient with a partial<br />
UAO is still conscious and able to ventilate,<br />
and vasoconstriction is desired to decrease<br />
mucosal edema.<br />
Racemic epinephrine administered by<br />
means of a nebulizer has been proven to be<br />
effective in treating croup (laryngotracheobronchitis)<br />
in the pediatric population<br />
decreasing morbidity, mortality, and hospital<br />
stay (6). Conversely, racemic epinephrine is<br />
not effective in the treatment of epiglottitis<br />
and may be deleterious (7).<br />
Racemic epinephrine also is used to treat<br />
postextubation laryngeal edema, which has<br />
been reported to occur from 2.3% to 6.9% (8).<br />
The typical case is that of a patient, breathing<br />
easily for the first two or three hours, followed<br />
by the gradual progression of dyspnea,<br />
inspiratory stridor, and increased work of<br />
breathing. In this situation repeat racemic<br />
epinephrine treatments can be used as a temporary<br />
measure until the acute swelling and<br />
inflammation subsides. These patients should<br />
remain in the intensive care unit under careful<br />
observation until it is confirmed that the<br />
UAO has resolved or greatly improved.<br />
Corticosteroids<br />
Corticosteroids have been used to treat UAO<br />
because of their potential beneficial effect in<br />
<strong>Upper</strong> <strong>Airway</strong> <strong>Obstruction</strong> 393<br />
reducing airway edema. Randomized trials<br />
have confirmed the usefulness of corticosteroids<br />
in the treatment of croup with<br />
decreases in the need for intubation and<br />
hospital stay (9). However the treatment of<br />
epiglottitis with steroids is controversial and<br />
often contraindicated (5).<br />
Experimental studies in animals have<br />
shown that corticosteroids given at the time<br />
of extubation decrease capillary dilatation<br />
and permeability as well as edema formation<br />
and inflammatory cells infiltration. The preventive<br />
use of steroids for postextubation<br />
laryngeal edema is until now widely accepted.<br />
However, a placebo controlled, double-blind,<br />
multicenter study showed that dexamethasone<br />
does not prevent laryngeal edema after<br />
tracheal extubation, regardless of intubation<br />
duration (8-10).<br />
Heliox<br />
Heliox, a helium–oxygen gas mixture, is<br />
effective in reducing the work of breathing by<br />
decreasing airway resistance to turbulent<br />
flow in the density-dependent pressure drop<br />
across the airway obstruction. Heliox has<br />
been used in several conditions including<br />
postextubation laryngeal edema, tracheal<br />
stenosis or extrinsic compression, status<br />
asthmaticus, and angioedema (11,12).<br />
To be effective, the helium–oxygen ratio<br />
must be at least 70:30. Unfortunately, most<br />
patients with UAO also have lung disease with<br />
varying degrees of hypoxemia preventing the<br />
use of heliox at effective concentrations.<br />
Although the work of breathing and dyspnea<br />
improves to some degree with the use of<br />
heliox, the mechanical obstruction is still in<br />
place. The use of heliox in patients with<br />
severe UAO should only be used to provide<br />
temporary support pending definitive diagnosis<br />
and management.<br />
Endotracheal Intubation<br />
In most cases of UAO, the patency of the<br />
upper airway can be reestablished with endotracheal<br />
intubation after rapid assessment of<br />
the patient’s airway anatomy. Evaluation of
Ch37 7/10/08 9:47 AM Page 394<br />
394 Systemic Disorders<br />
mouth opening (>40 mm), dentition, cervical<br />
spine mobility (flexion-extension), thyromental<br />
distance (normal is >3 finger breadths)<br />
and the function of the temporomandibular<br />
joints are key to subsequent success and<br />
avoidance of complications (13,14).<br />
Orotracheal intubation under direct visualization<br />
with a laryngoscope is the most<br />
commonly used route for emergency intubations.<br />
In patients with distorted airway<br />
anatomy or suspected cervical spine injury,<br />
fiberoptic bronchoscopy can be used to guide<br />
the intubation. The endotracheal tube is positioned<br />
over a bronchoscope; the operator<br />
introduces the fiberoptic bronchoscope into<br />
the patient’s mouth or nose and advances it<br />
through the vocal cords into the trachea. The<br />
endotracheal tube is then advanced over the<br />
bronchoscope.<br />
A prompt and successful intubation in a<br />
patient with UAO allows restoration of adequate<br />
ventilation and oxygenation and the<br />
performance of further diagnostic and therapeutic<br />
procedures.<br />
Surgical Interventions<br />
Overall, emergency laryngotracheal intubation<br />
is effective in approximately 97% of<br />
cases (13). Thus, a surgical airway is needed<br />
in only 3% of such emergencies. The need for<br />
an immediate surgical airway must be evaluated<br />
considering the potential difficulties<br />
associated with emergency intubation. In<br />
cases of UAO the surgical airway is considered<br />
emergently in cases of laryngotracheal<br />
trauma, foreign body lodged in the pharyngolaryngeal<br />
area, or severe anatomic deformity<br />
caused by trauma.<br />
When surgical airway management is<br />
required, cricothyroidotomy is the procedure<br />
of choice in the emergency setting; it is faster<br />
(average 30 sec), simpler, and more likely to<br />
be successful than tracheotomy. Intraluminal<br />
diameter of the trachea is narrowest at the<br />
level of the cricoid; there is concern that prolonged<br />
use of a cricothyroidotomy may cause<br />
subglottic injury and lead to subglottic narrowing.<br />
It is recommended that cricothy-<br />
roidotomy be converted to formal tracheotomy<br />
if longer than 72 hours of use is<br />
anticipated.<br />
Tracheostomy is probably the last option<br />
available to establish an airway in acute UAO.<br />
Laryngeal trauma is a relative contraindication<br />
to cricothyroidotomy and laryngotracheal<br />
intubation; it is the only indication for<br />
emergency tracheostomy. This procedure is<br />
time-consuming and requires expertize and<br />
attention to detail. Comparison of emergent<br />
versus elective tracheotomy reveals a twofold<br />
complication rate in the former because of<br />
the time spent on isolating the trachea as a<br />
result of commonly occurring bleeding (13,15).<br />
Cricothyroidotomy has a higher success<br />
rate than tracheostomy; it also has better<br />
patient neurologic outcome based primarily<br />
on less time required for the procedure (11).<br />
Overall, patients requiring an emergency<br />
surgical airway have a relatively high mortality<br />
(15).<br />
Laser Therapy<br />
Carbon dioxide or neodymium:yttrium-aluminum-garnet<br />
(Nd:YAG) laser therapy can be<br />
used to treat intraluminal tracheobronchial<br />
lesions once the UAO has been stabilized with<br />
a secure airway. Although the onset of airway<br />
compromise is usually gradual, some patients<br />
remain asymptomatic despite airways that<br />
are only two to three millimeter in diameter.<br />
These patients only develop dyspnea on exercise<br />
or when complete blockage results from<br />
mucus, bleeding, or inflammation with<br />
swelling. Laser therapy can be used to excise<br />
tracheal webs, to treat benign obstructive<br />
lesions, or as palliative therapy for malignant<br />
tracheobronchial lesions.<br />
Tracheal Stenting<br />
Tracheal stents placed using either rigid or<br />
flexible bronchoscopy can be helpful to maintain<br />
a patent airway in patients with tracheal<br />
obstruction caused by benign or malignant<br />
conditions. <strong>Airway</strong> resection and reconstruction<br />
provide the definitive correction, but
Ch37 7/10/08 9:47 AM Page 395<br />
many patients have unresectable disease. For<br />
these patients, therapeutic bronchoscopy<br />
provides rapid palliation that can be lifesaving<br />
and improve quality of life. Benign<br />
lesions can be managed with dilation, with or<br />
without laser resection. Malignant lesions<br />
often require core out of the tumor with a<br />
rigid bronchoscope followed by laser, photodynamic<br />
therapy, brachytherapy, cryotherapy,<br />
or electrocautery. <strong>Airway</strong> stents are a valuable<br />
adjunct to these techniques and can provide<br />
prolonged palliation from an unresectable<br />
recalcitrant benign stenosis or rapidly recurrent<br />
endoluminal tumor.<br />
Neither silicone nor the available metal<br />
stents conform to all the ideal characteristics<br />
desired for an endobronchial stent. The silicone<br />
stent has the advantages of being easily<br />
repositioned or removed, causing minimal<br />
granulation, and being inexpensive. Its disadvantages<br />
are the need for rigid bronchoscopy<br />
and general anesthesia, reduced inner diameter,<br />
and the potential for being dislodged or<br />
distorted (16,17). The expandable metal stent<br />
has the advantages of being easily delivered<br />
with flexible bronchoscopy, having minimal<br />
migration, and conforming well to the<br />
anatomy of the airway. The major disadvantage<br />
is that it is permanent and can cause significant<br />
granulation tissue within the stent<br />
(17). Because of the intrinsic problems associated<br />
with airway stents, regardless of type,<br />
it is important to remember that these<br />
patients require lifelong management and<br />
are at risk for development of stent obstruction<br />
or migration. In one series, 41% of<br />
patients required additional endoscopic<br />
interventions to maintain airway patency. In<br />
patients with benign disease and normal life<br />
expectancy (e.g., relapsing polychondritis) a<br />
much higher percentage of patients require<br />
further interventions (16,17).<br />
Complications<br />
Pulmonary Edema<br />
Postobstructive pulmonary edema is the sudden<br />
onset of edema following UAO without<br />
evidence of any other underlying cardiopul-<br />
<strong>Upper</strong> <strong>Airway</strong> <strong>Obstruction</strong> 395<br />
monary condition (18-20). There are two<br />
types of postobstructive pulmonary edema.<br />
Type I follows a sudden, severe airway<br />
obstruction such as postextubation laryngospasm,<br />
epiglottitis, croup, strangulation,<br />
choking, and hanging. Type I is associated<br />
with any cause of acute UAO. Type II pulmonary<br />
edema develops after surgical relief<br />
of long-term UAO. Reported causes include<br />
tonsillectomy and removal of upper airway<br />
tumors. Postobstructive pulmonary edema<br />
usually occurs within one hour of a precipitating<br />
event but it has reported to occur up to<br />
six hours later. The exact pathogenesis is<br />
unclear but the current theory is that young<br />
patients are able to generate extremely high<br />
negative intrathoracic pressure, which<br />
increases venous return, decreases cardiac<br />
output, and causes fluid transudation into<br />
the alveolar space. The cause of type II postobstructive<br />
pulmonary edema is less clear,<br />
but it appears that the obstructing lesion<br />
produces a modest level of positive endexpiratory<br />
pressure (PEEP) and increases<br />
end-expiratory lung volume. The sudden<br />
removal of this PEEP may then lead to interstitial<br />
fluid transudation and pulmonary<br />
edema (20).<br />
The treatment of postobstructive pulmonary<br />
edema is supportive with supplemental<br />
oxygen, intubation, and application of low<br />
levels of PEEP (5 cm H 2 O). The role of diuretics<br />
in this setting is unclear. Most patients<br />
respond promptly to appropriate treatment<br />
and have full recovery.<br />
Summary<br />
<strong>Upper</strong> airway obstruction is a potentially fatal<br />
emergency faced by critical care physicians. It<br />
can be caused by myriad conditions that will<br />
require a particular treatment after appropriate<br />
diagnosis. Regardless of the specific cause,<br />
the patient with UAO must be carefully monitored<br />
in the ICU for impending respiratory<br />
failure. A secure and patent airway should be<br />
established if clinical deterioration is seen.<br />
Pharmacologic interventions have limited
Ch37 7/10/08 9:47 AM Page 396<br />
396 Systemic Disorders<br />
usefulness in the setting of acute mechanical<br />
UAO. The critical care physician must be competent<br />
in the full range of airway access procedures.<br />
Overall, patients requiring an<br />
emergency surgical airway have a poor neurological<br />
outcome and higher mortality. Figure<br />
37-5 gives an algorithmic approach to management<br />
of UAO.<br />
REFERENCES<br />
Impending respiratory failure<br />
Is ET intubation<br />
possible?<br />
Yes<br />
No<br />
Urgent establishment of<br />
patent airway<br />
Direct or fiberoptic<br />
intubation<br />
Crycothyroidotomy vs<br />
Tracheotomy<br />
1. Jacobson S. <strong>Upper</strong> airway obstruction. Emerg<br />
Med Clin North Am. 1989;7:205-17.<br />
2. Khosh MM, Lebovics RS. <strong>Upper</strong> airway obstruction.<br />
In: Parrillo JE, Dellinger RP, eds. Critical<br />
Care Medecine. St. Louis: Mosby; 2001:808-25.<br />
3. King EG, Sheehan GJ, McDonell TJ. <strong>Upper</strong> airway<br />
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4. Aboussouan L, Stoller JK. Diagnosis and management<br />
of upper airway obstruction. Clin<br />
Chest Med. 94119;5:35-53.<br />
Stridor suggestive of<br />
UAO<br />
Quick history and physical<br />
examination<br />
Gradual onset and mild<br />
symptoms<br />
Selection of appropriate ancillary<br />
studies:<br />
• Bronchoscopy<br />
• CT upper airway<br />
• Spirometry<br />
Figure 37-5 Algorithm for management of upper airway obstruction. (CT = computed tomography;<br />
ET = endotracheal; UAO = upper airway obstruction.)<br />
5. Dickison AE. The normal and abnormal pediatric<br />
airway. Recognition and management of<br />
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6. Quan L. Diagnosis and treatment of croup. Am<br />
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7. Kissoon N, Mitchell I. Adverse effects of<br />
racemic epinephrine in epiglottitis. Pediatr<br />
Emerg Care. 85119;143-4.<br />
8. Darmon JY, Rauss A, Dreyffus D, et al. Evaluation<br />
of risk factors for laryngeal edema after tracheal<br />
extubation in adults and its prevention by dexamethasone.<br />
Anesthesiology. 1992;77:245-51.<br />
9. Kairys SW, Olmstead EM, O’Connor GT.<br />
Steroid treatment of laryngotracheitis: a metaanalysis<br />
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Pediatrics. 1989;83:683-93.<br />
10. McCulloch TM, Bishop MJ. Complications of<br />
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1991;12:507-21.<br />
11. Boorstein JM, Boorstein SM, Humphries GN,<br />
et al. Using helium–oxygen mixtures in the<br />
emergency management of acute upper airway<br />
obstruction. Ann Emerg Med. 1989;18:688-90.<br />
12. Curtis JL, Mahlmeister M, Fink JB, et al.<br />
Helium–oxygen gas therapy. Chest. 1986;90:<br />
455-7.
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13. Feller-Kopman D. Acute complications of artificial<br />
airways. Clin Chest Med. 2003;24:445-55.<br />
14. Steinert R, Lullwitz E. Failed intubation with<br />
case reports. HNO. 1987;35:439-42.<br />
15. Goldberg J, Levy PS, Morkovin V, Goldberg JB.<br />
Mortality from traumatic injuries: a casecontrol<br />
study using data from the national<br />
hospital discharge survey. Med Care. 1983;21:<br />
692-704.<br />
16. Wood DE, Liu YH, Vallieres E, et al. <strong>Airway</strong><br />
stenting for malignant and benign tracheobronchial<br />
stenosis. Ann Thorac Surg. 2003;76:<br />
167-74.<br />
<strong>Upper</strong> <strong>Airway</strong> <strong>Obstruction</strong> 397<br />
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