Physical Examination
The patient must be initially subjected to a simple inspection
from the front and side to identify obvious problems such as massive obesity, cervical
collars, traction devices, external trauma, or any indications of respiratory difficulty
such as stridor. The presence of ear and hand anomalies often suggests the presence
of a difficult airway. Nostril
TABLE 42-2 -- Selected congenital syndromes associated with difficult endotracheal intubation
|
Syndrome |
Description |
|
Down |
Large tongue, small mouth make laryngoscopy difficult; small
subglottic diameter possible |
|
Laryngospasm is common. |
|
Goldenhar (oculoauriculo-vertebral anomalies) |
Mandibular hypoplasia and cervical spine abnormality make laryngoscopy
difficult. |
|
Klippel-Feil |
Neck rigidity because of cervical vertebral fusion |
|
Pierre Robin |
Small mouth, large tongue, mandibular anomaly; awake intubation
essential in neonate |
|
Treacher Collins (mandibulofacial dysostosis) |
Laryngoscopy is difficult. |
|
Turner |
High likelihood of difficult intubation |
size and patency are essential to establish before considering nasal intubation.
A large beard may make physical examination, mask ventilation, and direct laryngoscopy
more difficult. Trimming or removing the beard should be considered when the airway
is judged to be difficult or when the surgery (e.g., cervical, intracranial) prevents
circumferential securement of the tracheal tube.
Edentulous patients are seldom difficult to intubate unless other
associated problems are severe. Protuberant upper incisors can make laryngoscopy
difficult and expose the teeth to damage. Isolated loose teeth are particularly
prone to damage. These should be noted along with the location of crowns, bridges,
braces, and other significant dental work. Bridges and dentures should be removed
if possible unless dentures significantly improve mask fit. Very loose teeth are
best removed before laryngoscopy to avoid aspiration of a tooth. Patients should
be warned of likely damage to teeth in person and in the preoperative note.
Mouth opening, which is largely a function of the temporomandibular
joint, is of prime importance to allow the insertion of a laryngoscope blade and
subsequent glottic visualization. Adults should be able to open their mouths so
that there is a 30- to 40-mm distance (about two large fingerbreadths) between upper
and lower incisors.[6]
A problem with mouth opening
should not be underestimated because it can make visualization of any laryngeal structures
impossible. It may be risky to assume that limited mouth opening is caused by a
spasm that will reverse after neuromuscular blockade. Conversely, in some patients
able to open the mouth widely in the awake state, adequate mouth opening in the anesthetized
state was possible only when the mandible was pulled forward.[7]
Previous transtemporal neurosurgery may produce severe limitation in mouth opening
that was not present during the original anesthesia.
The oral cavity examination is aimed at identifying a long, narrow
mouth with a high-arched palate that is associated with difficult intubation. A
large tongue in
TABLE 42-3 -- Selected pathologic states that influence airway management
|
Pathologic State |
Difficulty |
|
Infectious epiglottitis |
Laryngoscopy may worsen obstruction. |
|
Abscess (submandibular, retropharyngeal, Ludwig's angina) |
Distortion of airway renders mask ventilation or intubation extremely
difficult. |
|
Croup, bronchitis, pneumonia (current or recent) |
Airway irritability with tendency for cough, laryngospasm, bronchospasm |
|
Papillomatosis |
Airway obstruction |
|
Tetanus |
Trismus renders oral intubation impossible. |
|
Traumatic foreign body |
Airway obstruction |
|
Cervical spine injury |
Neck manipulation may traumatize spinal cord. |
|
Basilar skull fracture |
Nasal intubation attempts may result in intracranial tube placement. |
|
Maxillary or mandibular injury |
Airway obstruction, difficult mask ventilation, and intubation;
cricothyroidotomy may be necessary with combined injuries |
|
Laryngeal fracture |
Airway obstruction may worsen during instrumentation. |
|
Endotracheal tube may be misplaced outside larynx and may worsen
the injury. |
|
Laryngeal edema (postintubation) |
Irritable airway, narrowed laryngeal inlet |
|
Soft tissue, neck injury (edema, bleeding, emphysema) |
Anatomic distortion of airway |
|
Airway obstruction |
|
Neoplastic upper airway tumors (pharynx, larynx) |
Inspiratory obstruction with spontaneous ventilation |
|
Lower airway tumors (trachea, bronchi, mediastinum) |
Airway obstruction may not be relieved by tracheal intubation. |
|
Lower airway is distorted. |
|
Radiation therapy |
Fibrosis may distort airway or make manipulations difficult. |
|
Inflammatory rheumatoid arthritis |
Mandibular hypoplasia, temporomandibular joint arthritis, immobile
cervical spine, laryngeal rotation, and cricoarytenoid arthritis make intubation
difficult and hazardous. |
|
Ankylosing spondylitis |
Fusion of cervical spine may render direct laryngoscopy impossible. |
|
Temporomandibular joint syndrome |
Severe impairment of mouth opening |
|
True ankylosis |
|
|
False ankylosis (burn, trauma, irradiation, temporal
craniotomy) |
|
|
Scleroderma |
Tight skin and temporomandibular joint involvement make mouth
opening difficult. |
|
Sarcoidosis |
Airway obstruction (lymphoid tissue) |
|
Angioedema |
Obstructive swelling renders ventilation and intubation difficult. |
|
Endocrine or metabolic acromegaly |
Large tongue, bony overgrowths |
|
Diabetes mellitus |
May have reduced mobility of atlanto-occipital joint |
|
Hypothyroidism |
Large tongue and abnormal soft tissue (myxedema) make ventilation
and intubation difficult. |
|
Thyromegaly |
Goiter may produce extrinsic airway compression or deviation. |
|
Obesity |
Upper airway obstruction with loss of consciousness |
|
Tissue mass makes successful mask ventilation unlikely. |
relation to oral cavity size may make laryngoscopy more difficult. Mallampati and
colleagues[8]
emphasized the importance of the base
of the tongue in determining the difficulty of laryngoscopy. If the faucial pillars
(palatoglossal and palatopharyngeal arches) and uvula cannot be seen in a seated,
vocalizing patient with the tongue protruding ( Fig.
42-1
and Fig. 42-2
),
visualization of the glottis is likely to be more difficult than in patients in whom
these structures are readily visible. An increase in Mallampati score may occur
during pregnancy and correlates with the slightly higher rate of difficult laryngoscopy
in this population.[9]
The distance from the inner surface of the mandible to the hyoid
bone during neck extension should be at least two large fingerbreadths in adults.
If the thyromental space is examined, the comparable distance is 50 mm, which is
about three large fingerbreadths. There appears to be no difference in the results
of using the hyomental or thyromental distances, except that the thyroid cartilage
may be easier to locate. These areas are important because the laryngoscope displaces
the tongue into this space, and exposure of the glottis may be inadequate if the
space is narrowed or noncompliant. A receding or hypoplastic mandible results in
a situation often referred
Figure 42-1
Illustration of patient in whom faucial pillars, soft
palate, and uvula are visible. (From Mallampati SR, Gatt SP, Guigino LD,
et al: A clinical sign to predict difficult tracheal intubation: A prospective
study. Can Anaesth Soc J 32:429, 1985.)
to as an anterior larynx or high larynx by clinicians. An inability to bring the
lower incisors edge to edge with the upper incisors (i.e., impaired mandibular protrusion)
is an important warning that laryngoscopy may be difficult.[10]
Conversely, if the lower incisors can be brought forward to bite the upper lip beyond
the vermilion, mandibular displacement can be expected to aid intubation. The latter
case would seem to diminish the impact of the Mallampati score.
Figure 42-2
Illustration of patient in whom none of the three pharyngeal
structures is visible. (From Mallampati SR, Gatt SP, Guigino LD, et al:
A clinical sign to predict difficult tracheal intubation: A prospective study.
Can Anaesth Soc J 32:429, 1985.)
The neck is examined for masses, fixation of the trachea, and
mobility, particularly with extension. A patient with a short, thick, muscular neck
(e.g., the classic football lineman) with a full set of teeth may pose difficult
mask ventilation and very difficult laryngoscopy. Exposure of the larynx requires
some degree of flexion (about 35 degrees) in the lower cervical spine and extension
(about 80 degrees) in the upper cervical spine, especially at the atlanto-occipital
joint ( Fig. 42-3
). With
the curved MacIntosh blade, the maximal cervical motion occurs at the atlanto-occipital
and atlantoaxial joints.[11]
The patient should
be asked to flex and extend the neck maximally, provided
Figure 42-3
Schematic diagram demonstrating the head position for
endotracheal intubation. A, Successful direct laryngoscopy
for exposure of the glottic opening requires alignment of the oral, pharyngeal, and
laryngeal axes. B, Elevation of the head about 10
cm with pads below the occiput and with the shoulders remaining on the table aligns
the laryngeal and pharyngeal axes. C, Subsequent
head extension at the atlanto-occipital joint creates the shortest distance and most
nearly straight line from the incisor teeth to glottic opening.
there are no contraindications such as suspected or known cervical spine fracture,
severe cervical spondylosis with cord or vertebral artery symptoms on motion, or
rheumatoid arthritis with atlantoaxial subluxation. Extension of the head can be
quantitated by determining the angle of head extension, with the lower neck flexed
about 30 to 40 degrees in the sniffing position. Normal extension is 80 degrees,
with lesser degrees representing increasing limitation and increased potential for
difficult laryngoscopy. A hoarse voice or previous prolonged intubation or tracheostomy
should alert the clinician to the possibility of a stenotic airway at some level.
The combination of several minor physical anomalies may result in a difficult intubation
even when no one single factor is severely abnormal. A number of studies have attempted
to combine physical factors to predict difficult intubation with mixed results, but
it is not clear that these efforts represent an improvement over the clinical evaluation
of a seasoned clinician. Additional problems with preoperative airway assessment
tests are that they have only moderate interobserver reliability and depend on the
definitions of airway difficulties. Difficult intubations also occur occasionally
for reasons that are unexplained, and none of the available indices predicts all
difficult intubations. The truly life-threatening problem is the inability to ventilate
when intubation is difficult or impossible.
