Virtual Disaster Medicine

Training Center (VDMTC)

Module 1

Basic Review of Endotracheal Intubation

for Providers at a Mass Casualty

Review of Anatomy

There are two openings where air can enter the upper airway.  These are the nasopharynx and the oropharynx.

● the nasopharynx begins just posterior to the internal nasal cavity and extends to the soft palate.

● the oropharynx begins at the soft palate and extends to the hyoid bone.  The oropharynx serves as both a food and respiratory passageway.

The laryngopharynx begins at the level of the hyoid bone and connects posteriorly with the esophagus and anteriorly with the larynx.

The glottic opening is covered by the epiglottis.  The epiglottis moves freely to prevent aspiration of food from the oropharynx into the trachea.  During swallowing it covers the glottic opening.

PREOPERATIVE EVALUATION

Preoperative evaluations are performed on patients before receiving an anesthetic (including conscious sedation). The preoperative evaluation includes an assessment of anatomic characteristics that may make mask ventilation or intubation of the trachea difficult.  Basic standards for preanesthesia care (to include preoperative evaluations) have been outlined by the American Society of Anesthesiology^2,17.  These standards would be applicable to any patient whose airway is being managed, including conscious sedation.

Preoperative Evaluation of the Upper Airway

Preoperative evaluation of the Upper Airway includes dental examination, determination of the size of the tongue versus pharyngeal size; atlanto-occipital joint extension; and anterior mandibular space (thyromental distance).²

Problems with exposure.

Anterior Larynx

Prominent Upper Incisors

Large Posteriorly Located Tongue

Micrognathia  (small mandible)

Size of Tongue Versus Pharynx

The size of the tongue versus the oral cavity can be visually graded by assessing how much the pharynx is obscured by the tongue.  This is the basis for the Mallampati classification.^5,6  The Mallampati class (in isolation, as a sole method of airway evaluation), has met with only moderate success (low positive predictive value) in identifying patients who are subsequently found to have a difficult intubation.^7,8

This Mallampati classification is performed by asking the patient to sit with the head in a neutral position, the mouth opened maximally (normal opening of 50 to 60 mm) and the tongue protruded as far as possible.⁵  The examiner classifies the patient’s airway according to what pharyngeal structures are visible.  Patient phonation during the examination was shown to falsely improve the view.  When the entire uvula is visible (Class 1 airway), the laryngoscopic view is expected to be classified as Grade I (tracheal intubation by direct laryngoscopy expected to be easy) in contrast to the Class IV score where only the hard palate is seen, which is expected to be technically difficult or impossible.^2,5

Table 1 shows the Mallampati Classification

Atlanto-Occipital Joint Extension

Preoperative evaluation of cervical spine mobility (atlanto-occipital joint extension) can be performed by having the patient sit with the head erect facing the examiner and then extending the joint as much as possible.  Normal extension is 35 degrees.  Decreases in this range of motion may be associated with difficulties in aligning the oral and laryngeal axes during intubation.⁵

Anterior Mandibular Space

The anterior mandibular space is evaluated by asking the patient to maximally extend the head and measuring the distance from the notch of the thyroid cartilage to the tip of the mentum (thyromental distance).⁵   If the thyromental distance is less than 6 cm, the laryngeal axis will make a more acute angle with the pharyngeal axis.  This will make atlanto-occipital extension more difficult and create problems in aligning the laryngeal and pharyngeal axes.  This is typically encountered in patients with a receding mandible or short neck with large neck circumference. ^2,5,9

Dental Examination

A preoperative dental examination is needed to ascertain the presence of loose teeth, dental prostheses or other teeth or dental abnormalities.⁵   Loose dental prosthesis may be dislodged during the intubation process and result in aspiration.  Protruding incisors (buck teeth), may make it difficult to obtain an adequate laryngeal view during intubation.

PATIENTS WITH RECENT TRAUMA

In patients who have sustained a recent trauma, assessment of the stability of the cervical spine is critical. In appropriate patients, the presence of pain on movement should be assessed. Otherwise, radiographic examination may be required. ² The subject of airway exam with recent trauma will be the subject of a separate module. If the patient is wearing a neck brace it will lead to a lack of extension and possible increased difficulty in visualization of the airway.