Tintinalli's Emergency Medicine > Section 3: Resuscitative Problems and Techniques >
Chapter 18. Noninvasive Airway Management >
Anatomy and Pathophysiology
Prior to airway management procedures, when there is sufficient time, the physician
should:
1. Inspect the patient's mouth for size of teeth and for size and mobility of the jaw.
2. Open the patient's mouth and observe the palate, tongue, and oropharynx.
3. Flex the stable neck (in the absence of trauma), assess mobility, and place in the
sniffing position.
4. Examine the size and alignment of the neck.
5. Inspect the nasal openings for patency.
6. Listen for abnormal airway sounds such as stridor, hoarseness, or gurgling.
7. Ask the patient's history, if possible.
8. Be sure to have suction available at all times, especially during any procedures.
The anatomic airway (Figure 18-1) begins at the oral/nasal cavities and continues
posteriorly to the tongue/turbinates, the tonsils/adenoids; past the palate; through the
oropharynx; across the epiglottis, which protects the glottis (the narrowest portion of the
airway); past the false and true vocal cords; and into the larynx. Surrounding the larynx is
the thyroid cartilage, cricoid cartilage, and thyroid gland. The upper airway ends here.
The lower airway then continues to the trachea and into the lungs. Potential obstruction
may develop anywhere along this route. In infants and small children, the anatomy is
somewhat different than in the adult. The tongue is relatively larger in relation to the
mandible. The glottis is higher and more anterior and the vocal cords are angled more
anteriorly and inferiorly. The epiglottis is large and floppy and may lie against the
posterior wall of the pharynx.
Fig. 18-1.
The anatomic airway.
Airway Obstruction
Table 18-1 lists potential causes of upper airway obstruction. Basic management of the
obstructed airway is discussed in Chap. 12. Most of these entities cause soft tissue
swelling or themselves are soft tissue masses that compromise the upper airway, but a
few need mentioning. Certain medical diseases, such as respiratory syncytial virus (RSV)
and cystic fibrosis, produce copious secretions in the upper airway that can lead to partial
or complete occlusion. Angioedema may present with soft tissue swelling sufficient to
preclude an oral airway, requiring a nasal pharyngeal airway, nasotracheal intubation, or
surgical intervention to reestablish patency. Laryngospasm, the feared complication of
any invasive airway technique, needs to be considered in any patient with a compromised
airway, especially in children. It is defined as closure of the glottis by the constriction of
intrinsic/extrinsic laryngeal muscles, which can completely restrict ventilation. This
pathophysiologic state often persists long after the stimulus has ceased. Laryngospasm
may occur secondary to contact with the upper airway receptors on the tongue, palate,
and oropharynx. Light touch to the upper airway, traction on the pelvic/abdominal
viscera, chemical irritation, secretions, blood, water, and vomitus may all cause
laryngospasm. Hypoxia and hypercapnia depress the activity of laryngeal adductor
neurons, so laryngospasm is somewhat self-limited. Laryngospasm and bronchospasm
occur more frequently in children and particularly following a recent respiratory tract
infection.
Table 18-1 Causes of Upper Airway Obstruction
Congenital/Genetic Infectious Medical Trauma/Tumor
Large tonsils Tonsillitis Cystic fibrosis Laryngeal trauma
Macroglossia Peritonsilar abscess Angioedema Hematoma/masses
Micrognathia Retropharyngeal abscess Laryngospasm Smoke inhalation
Neck masses Pretracheal abscess Airway muscle relaxation Thermal injuries
Large adenoids Epiglottitis Inflammatory Foreign body
Laryngitis/RSV* Asthma
Ludwig angina
*Respiratory syncytial virus.
Altered mental status, somnolence, or even sleep can depress the intrinsic and extrinsic
muscle tone of the airway and produce obstruction. Some authors question the longstanding belief that the tongue falling back and occluding the lower pharynx is the major
cause of airway obstruction in the somnolent or comatose patient. Recently, it was shown
that during anesthesia in the supine patient, the tongue does, in fact, displace posteriorly,
but it does not appear to occlude the pharynx. Upper airway obstruction in the
unconscious patient occurs primarily because the epiglottis occludes the laryngeal inlet
because of intrinsic muscle relaxation, which can be relieved simply by extending the
neck. Extension of the neck and anterior displacement of the mandible moves the hyoid
bone anteriorly and, in turn, lifts the epiglottis away from the laryngeal inlet. In a supine
individual, the degree of extension of the head required to open the airway depends on
elevation of the occiput above the horizontal plane. Relative to the neck, the more the
occiput is elevated (to a degree), the less extension is required to open the airway, which
explains why patients with airway compromise need to have their heads in the "sniffing"
position. One can place a folded towel (not rolled) or foam rubber device underneath the
patient's occiput (not neck) to create this position. Flexion of the neck has a marked effect
of closing the airway, specifically the oropharynx. Recent magnetic resonance imaging
(MRI) studies show that the soft palate also relaxes significantly during sedation,
partially occluding the nasopharynx and causing complete obstruction when the patient is
fully anesthetized. Moreover, extension of the anterior tongue does not appear to relieve
this obstruction.1
Esophageal foreign bodies can also obstruct the airway. They can impinge upon the
larynx or trachea, causing either acute or subacute obstruction. Some foreign bodies, such
as large fruit pits, may have been present for some time; thus, there may not be a history
of swallowing or choking on an object.
Oral/Nasal Airways
The oral airway (Figure 18-2) is an "S"-shaped, rigid instrument that is used to prevent
the base of the tongue from occluding the hypopharynx. It should be used to maintain the
airway only in a patient with an absent gag reflex. The operator places the oral airway
over the tongue, being careful not to push it further into the hypopharynx. A tongue blade
can be used to aid insertion. The concave portion is placed cephalad, rotated 180 degrees,
or aimed toward the ear and rotated 90 degrees inferiorly to hold the tongue away from
the pharyngeal wall. It can also be used as a bite block during orotracheal intubation.
Fig. 18-2.
An oral airway.
A nasal airway (nasopharyngeal tube) (Figure 18-3) is made of a pliable material that
allows it to be placed into the nostril of a somnolent patient with an intact gag reflex. The
nasal airway is a wonderful tool that can be quickly placed in a sonorous patient who may
have decreased pharyngeal muscle tone and an obstructing soft palate and tongue. It
allows air to bypass such obstructions, and if topical anesthesia is used as a lubricant,
may ease subsequent passage of a nasogastric tube. The nasopharyngeal tube should be
inserted into the most patent nostril (with the tip lubricated, ideally with a topical
anesthetic such as lidocaine jelly) horizontal to the palate, and advanced until maximal
airflow is heard. It is important to use the correct size tube and to avoid inserting it far
enough to stimulate the gag reflex.
Fig. 18-3.
Nasal airways.
The Bag-Valve-Mask Unit
The bag-valve-mask (BVM) unit (Figure 18-4) is a self-inflating bag with a
nonrebreathing valve that can be attached to a face mask. This design allows room air or
oxygenated air to be manually delivered into the victim's lungs after any obstruction has
been eliminated. This apparatus can be used initially while preparing for definitive
airway maintenance. After the mask is placed, the handler clamps it snugly to the face.
The thumb and index finger grasp the mask while the other fingers grasp the chin and
pull it forward to hyperextend the stable neck. The other hand compresses the bag,
expelling air into the patient's respiratory tree. This procedure can be used to manage
respiratory failure temporarily, to assist poor inspiratory effort, or to temporize
respiratory fatigue. The most common problem with a one-person operation is air leaks
around the mask. A two-person operation employs two hands to hold the mask flush and
has been shown to result in more effective ventilation.2 Placement of an oral or nasal
airway further facilitates airflow. The BVM unit may also be used prior to rapid-sequence
intubation (RSI) to quickly assess the ease of BVM ventilation in cases where oral
intubation fails. After an intubation, the BVM unit can be attached to the proximal end of
the endotracheal tube.
Fig. 18-4.
Bag-valve-mask unit.
To deliver 100 percent oxygen, there must be a reservoir with the same volume as the bag
and an oxygen flow rate equal to the respiratory minute volume of the patient. By using a
2.5-L reservoir bag with an oxygen flow of 15 L per min, 100 percent oxygen can
theoretically be delivered, although most nonrebreathers deliver about 75 percent oxygen.
Similarly, a demand valve attached to the reservoir port of the ventilation bag will deliver
a high concentration of oxygen.
Esophageal Airways
Esophageal obturator airways (EOAs) (Figure 18-5)—the pharyngotracheal lumen airway
and the esophageal tracheal Combitube—are all devices used in the prehospital setting
when oral endotracheal intubation is not a viable option. These devices are designed to be
placed in apneic, unconscious adults only.
Fig. 18-5.
A. Pharyngotracheal lumen airway. B. Esophageal tracheal Combitube. C.
Tracheoesophageal airway (used with permission).
Esophageal Obturator Airway/Esophageal Gastric Tube Airway
EOAs/esophageal gastric tube airways (EGTAs) are mentioned here only for historic
reasons. They are rarely used now. The original primary benefit, placement without direct
laryngeal visualization, has been supplanted by other more efficacious devices. The
EGTA is a modification of the EOA and has an open distal tube containing a valve that
allows passage of a nasogastric tube. Compared with the endotracheal tube (ETT),
ventilation and oxygenation studies reveal varying results but suggest that the EOAs are
adequate during cardiac arrest.2 One study showed that some physicians had never seen
an EOA, and unfamiliarity is reason enough to avoid using this tool.
Pharyngotracheal Lumen Airway
The pharyngotracheal lumen airway (PTLA) (Figure 18-5A) is another two-tubed, cuffed
airway that seals the oropharynx proximally and occludes the esophagus distally,
allowing for ventilation through the short tube. There is no need for a face-to-mask seal.
If the trachea is intubated by the long tube, ventilation can occur through the lumen,
similar to an ETT.
Esophageal Tracheal Combitube
The esophageal tracheal Combitube (ETC) (Sheridan Catheter Corp.) (Figure 18-5B) is a
plastic twin-lumen tube with a proximal low-pressure cuff that seals the pharyngeal area
and a distal cuff that seals the esophagus, allowing ventilation between the cuffs. The
proximal seal also removes the need for a facemask and, as compared with the PTLA,
minimizes dental damage to the cuff. The distal cuff is similar to an ETT and serves to
seal either the esophagus or the trachea when inflated. If the distal tube enters the
esophagus, perforations in the esophageal lumen serve to ventilate the patient. If the
trachea is intubated, the patient is ventilated directly, as with the cuffed ETT.
Tracheoesophageal Airway
The tracheoesophageal airway (TEA) (Figure 18-5C) is a standard ETT attached to a
ventilation mask with two ports, one for the ETT and the other for oropharyngeal mask
ventilation. It is designed to function equally well if inserted into the trachea or the
esophagus. Tracheal intubation is facilitated by using cricoid pressure and extending the
neck. While the tube is in the trachea, the cuff is inflated and the patient is ventilated
normally. While the tube is in the esophagus, the patient is ventilated through the mask
and the ETT allows for gastric venting or decompression.
Laryngeal Mask Airway
The laryngeal mask airway (LMA) (Intavent, Ltd.) (Figure 18-6) was developed by
Brain, in 1983, as another artificial airway that can be placed blindly yet can provide a
positive-pressure airway. The LMA consists of a tubular oropharyngeal airway similar to
the ETT, but it is shorter and has a distal silicone laryngeal mask (balloon-type bulb) that
inflates and provides a seal around the larynx. The LMA, when placed, is similar to other
esophageal airways in that it can be inserted without manipulation of the patient's head.
Because of its large diameter and short length, intubation of the bronchi or esophagus is
circumvented. The hypopharynx, which is adapted to the passage of food, is less sensitive
to a foreign body than the larynx and vocal cords, which have sensitive, protective
reflexes.
Fig. 18-6.
A. Laryngeal mask airway (LMA). B. LMA diagram showing placement at the larynx
(used with permission).
Many published cases show the LMA to be an effective alternative when the ETT fails
because of nonvisualization of the cords secondary to ETT difficulty, airway masses, or
cervical pathology.3 One study of LMA use by nonphysician emergency personnel in
fasting patients found it easier to place than the ETT. In this study, there was no failure in
LMA placement, whereas 21 percent of ETT placement attempts failed. Furthermore, the
LMA required only half as many attempts and one-fifth the time to perform, and was
rated equal to the ETT as an airway by anesthesiologists.4 Complications of the LMA
include partial or complete respiratory obstruction (approximately 3 percent) and general
failure to protect against aspiration of gastric contents. The LMA is also inadequate in
severe chronic obstructive pulmonary disease (COPD) because of the high pressure
requirement.5 Applying cricoid pressure in the acute setting almost always impedes
insertion of the LMA and therefore reduces the chance of successful ventilation of the
patient.6 Therefore the LMA seems an effective alternative to the ETT when
endotracheal intubation fails or when cervical pathology exists.
Noninvasive Positive-Pressure Ventilation
The widespread use of noninvasive positive-pressure ventilation (NIPPV) for chronic
sleep apnea in the 1980s has prompted investigators to look at NIPPV in the acute setting
today. NIPPV can be described as an application of a preset volume/pressure of
inspiratory air through a face or nasal mask.
Inspiratory muscle fatigue is the final phase of ventilatory failure in patients with severe
reactive airway disease, COPD, and end-state pulmonary edema/pneumonia. The airway
resistance overcomes the patient's muscular ability to ventilate. An effective alternative to
the traditional ETT, with its potential complications, is noninvasive, mechanically
assisted ventilation with continuous positive airway pressure (CPAP) or bilevel positive
airway pressure (BiPAP).
Continuous Positive Airway Pressure
CPAP is one method of NIPPV where positive pressure is held constant throughout the
respiratory cycle and applied through a face or nasal mask. It recently received renewed
application in the treatment of patients with acute hypoxemic respiratory failure.7 CPAP
improves pulmonary function by reducing the work of breathing, maintaining inflation of
atelectatic alveoli, and improving pulmonary compliance. CPAP also improves
hemodynamics by reducing preload and afterload, therefore improving patient's cardiac
output in left ventricular failure.
NIPPV has been used to support patients with acute respiratory failure but has been
primarily studied in the intensive care setting. Only in the last decade have patient
diagnostic categories individually been studied in the emergency department (ED) using
CPAP. Those diseases include COPD, status asthmaticus, adult respiratory distress
syndrome (ARDS), acute cardiogenic pulmonary edema (ACPE), pneumonia, or
traumatic respiratory insufficiency. CPAP can be adjusted according to the patient's
clinical response. Pressures of 5 to 10 cm of H2O are most commonly used, and
pressures above 15 are rare.
In early published and unpublished studies, CPAP at 10 cm of H2O used in the hospital
and prehospital settings showed more rapid improvement of vital signs (heart rate,
respiratory rate, blood pressure) and oxygen saturation versus standard medical therapy
alone in ACPE patients.8 In other studies, using CPAP up to 10 to 12.5 cm H2O, there
was a significant improvement in Pao2, stroke volume index, lower rate-pressure product,
intrapulmonary shunt fraction, alveolar-arterial oxygen gradient, and, more importantly,
lower rate of tracheal intubation.9 After meta-analysis on the above studies, there was
found a statistically significant reduction in the need for tracheal intubation and possibly
a decrease in mortality.10
Bilevel Positive Airway Pressure
BiPAP is a method of NIPPV where positive airway pressure is used to assist the patient's
spontaneous ventilation at a "bilevel." The positive airway pressure increases during
inspiration and a positive expiratory pressure provides the physiological positive endexpiratory pressure known as PEEP. BiPAP machines respond to the patient's respiratory
cycle by alternating between a higher flow rate during the inhalation phase of respiration
and a lower flow rate during the exhalation phase.
The use of face-mask positive-pressure ventilation with acute exacerbation of COPD
avoids intubation up to 76 percent of the time.11 The benefits of BiPAP have been
proven most effectively in the setting of severe COPD and is now being evaluated for
ACPE. With the positive inspiratory pressure decreasing the work of breathing, and the
positive expiratory pressure providing the physiologic CPAP, BiPAP has a theoretical
advantage over CPAP alone. BiPAP has shown to reduce respiratory rate, dyspnea, and
allow a more rapid improvement in both oxygenation and ventilation versus CPAP. Most
recent studies using BiPAP with ACPE has shown to be an effective treatment in acute
respiratory failure when compared to conventional oxygen therapy alone.12–14
NIPPV has been shown to decrease need for endotracheal intubation (ETI), thus
decreasing the risks of ETI in the immunocompromised patient.15 A major goal in the
management of respiratory failure in the immunocompromised patient is avoiding ETI.
These patients are at high risk of pneumonia, bronchitis, sinusitis, and ETI increases the
risk of acquiring these diseases. In patients with pulmonary infiltrates, fever, and acute
respiratory failure, early NIPPV has shown to decrease rates of ETI and the serious
associated complications. Early NIPPV improves the likelihood of survival to hospital
discharge.15 One intensive care unit study showed that irrespective of the severity of the
patient's illness, the use of NIPPV reduced the risk of ventilation-associated pneumonia
and nosocomial infections.16
NIPPV decreases the requirement for mechanical support and lowers the average stay in
the intensive care unit, among hemodynamically stable patients with impending
respiratory failure.17 Studies also demonstrate arterial blood gas improvement, intubation
avoidance, and decreased respiratory rates with low complication risk.7,18
In the elderly, where the decision to intubate is more complex (because of age, illness, or
cancer), nasal-mask ventilation yielded improvements in PaO2 similar to those of other
studies (60 percent), but hypercarbia improved more slowly.19 NIPPV should be
considered for any patient where invasive respiratory support presents significant risk of
sequelae.
In the pediatric patient population, BiPAP appears to improve respiratory rate, heart rate,
PaCo2, and O2 saturation. It also decreases the need for intubation in obstructive apnea.
Trauma patients frequently have a significant loss of functional residual capacity (FRC)
that often leads to mild to moderate respiratory insufficiency. In such instances, CPAP
has been used to improve respiratory function and reduce hypoxemia.20 CPAP is helpful
in decreasing the work of breathing and improving FRC, thus preventing hypoxemia,
hypocarbia, and tachypnea. Criteria for NIPPV have included spontaneous respirations,
absence of respiratory acidemia/hypercarbia, intact mental status, a PaO2 above 65 mm
Hg, presence of a functioning nasogastric tube, and absence of severe maxillofacial
injury. Improvement may be seen starting at 5 cm H2O. Studies show that a mean CPAP
of 8.6 cm H2O meets therapeutic goals. Duration of therapy may range from a few hours
to 2 days. Trauma conditions that have been studied include pulmonary contusion, flail
chest, pneumothorax, hemopneumothorax, and multiple chest and abdominal
gunshot/stab wounds. In this setting, a functioning nasogastric tube and respective chest
tube placement, when indicated, are extremely important. Patients suffering high
esophageal or tracheal injuries should not be supported with a NIPPV. Maxillofacial and
basilar skull fractures are also contraindications to NIPPV by face mask. Because many
traumatized patients exhibit a remarkable capacity to breathe spontaneously and
improvements in hemodynamics are one of the benefits of using spontaneous ventilation
versus mechanical ventilation, CPAP/BiPAP is an appropriate adjunct for managing the
airway in the trauma patient assuming non-airway related indications for ETI do not
exist.
Technique
Nasal-mask or facial-mask ventilation employs a tight-fitting mask that allows for a
CPAP or BiPAP support system. The patient with impending respiratory failure receives
either continuous pressure or inspiratory/expiratory (bilevel) support, thus allowing a
decrease in inspiratory effort, rest for respiratory and accessory muscles, improvement of
gas exchange, avoidance of intubation, and improved comfort.11,21 A nasal-mask
protocol with BiPAP appears to be the most advanced protocol and appears to allow more
sensitive changes during the course of treatment (Figure 18-7). The nasal mask allows the
patient to eat, drink, and converse with the emergency staff. However, the nasal positivepressure ventilation (NPPV) (distinct from NIPPV) does allow for air leaks through the
mouth.
Fig. 18-7.
A patient with severe COPD on nasal BiPAP (used with permission).
The ideal BiPAP ventilator is small, relatively inexpensive, very mobile, and tolerates
some leaks. It is possible to set the inspiratory positive airway pressure (IPAP) and the
expiratory positive airway pressure (EPAP/PEEP) independently. Three modes of
ventilatory triggering are available: spontaneous, combined spontaneous/timed, and
timed. The proper-size mask should be chosen (allowing no mouth coverage) and tight
enough to allow a good, comfortable seal. Settings should include spontaneous mode,
IPAP set at 10, EPAP set at 3 cm H2O initially and increasing IPAP in 3-cm increments
and EPAP slowly. Continuing hypercarbic failure is treated by increasing IPAP alone in
3-cm increments.22 Caution must be applied when using NIPPV at pressures
approaching 15 cm H2O. There is evidence of increased risk of acute myocardial
infarction with higher NIPPV pressures. BiPAP, CPAP, and NIPPV at high pressures (15
cm H2O), may produce a greater fall in blood pressure because of a higher intrathoracic
pressure reducing myocardial perfusion.13,14
Complications
Known complications include difficulty with mask seal requiring multiple readjustments,
gastric distention, aspiration (rare), intolerance of the positive pressure, and facial skin
breakdown (with long-term use). These complications appear to occur infrequently, but
the most common intolerance is excessive respiratory secretions, which, in fact, may be a
relative contraindication to NPPV along with life-threatening epistaxis, or pre-existing
bullous lung disease. Other contraindications to NPPV are severe maxillofacial trauma
and potential basilar skull fracture where pneumocephalus may occur, pneumothorax,
pneumomediastinum, or hypotension due to or associated with intravascular volume
depletion. Another problem with mask ventilation is that using a conventional ventilator
can be difficult or even counterproductive because of the inadvertent triggering of alarms
in systems in masks not designed for this use. The BiPAP ventilatory system, which is
designed for NIPPV use, has been used with success, but may not be readily available in
the ED, and respiratory services may have to be contacted for this setup.
Application of NPPV provides ventilatory support for impending respiratory failure and
has been shown to decrease the workload of the respiratory muscles. Oxygen saturation,
Pao2, and pH remain stable or improve as compared with unassisted ventilation.
Therefore this technique may prove useful in respiratory failure when complication of
intubation is high.
This modality may decrease long-term hospital admissions, prevent unwanted intubations
in the elderly or severely ill, and circumvent borderline respiratory failure intubations.
Each patient must be closely monitored for tolerance of upper airway positive pressure
and for instability.
Patients who receive NIPPV need to be cooperative and should not have life-threatening
cardiac ischemia, dysrhythmias, or hypotension. NIPPV is inappropriate in patients who
have absent or agonal respiratory effort, or who produce excessive airway secretions.
Airway management and apparatus associated with NIPPV can be distracting. However,
medical treatment, such as in-line nebulized updrafts, anticholinergics, steroids, and
respiratory hygiene should proceed as appropriate.
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