# 22.12b Predictors of a Difficult Airway or Ventilation

It would be useful if practitioners could reliably predict which airways are likely to cause difficulty and which are not (Table 22-12).

This is particularly important when a medication-facilitated airway procedure is considered.

For patients for whom we anticipate difficulty, we could call for help in advance, consider deferring the procedure, consider managing the airway with BVM ventilation or an extraglottic device, or simply be better prepared by having different blades or devices, an introducer, a backup airway, and cricothyrotomy supplies immediately available.

In most emergency situations, however, a detailed airway assessment is not practical.

In many such cases, management must proceed even when airway assessment will be difficult because of patient acuity and a favorable risk-to-benefit analysis.

In general, EMS practitioners should prepare as though every intubation will be difficult.

Predictors of difficult BVM ventilation include facial trauma, facial hair, obesity, and lack of teeth (assuming you do not have the dentures to replace during BVM ventilation).

Other risk factors for difficult BVM ventilation demonstrated in the anesthesia literature include age over 55, history of snoring, Mallampati class 3 or 4 (discussed later), severely limited jaw protrusion, and thyromental distance (the distance between the thyroid notch and the bony point of the chin) of less than 6 cm.

Predictors of difficult extraglottic airway (EGA) device placement include limited mouth opening.

Situations in which an EGA can be inserted easily but ventilating the patient can be difficult include massive secretions, morbid obesity, severe pulmonary disease, and pathology below the device, such as inhalation burns, laryngeal trauma, and angioedema.

Commonly used predictors of difficult laryngoscopy and intubation include facial trauma/anomalies, increasing Mallampati class (discussed later), short thyromental distance, short sternomental distance (distance between the suprasternal notch and the bony point of the chin), limited mouth opening, limited neck mobility, obesity, and buckteeth.

Predictors of difficult surgical airway placement include situations in which the cricothyroid membrane cannot be located—such as morbid obesity, anterior neck trauma, prior radiation therapy, and infection such as Ludwig’s angina (a very serious skin infection that tracks down into the anterior neck, usually from a dental infection)—and situations in which a tumor, infection, swelling, or foreign body within the airway lumen prevents tube insertion even when the membrane can be located.

Various difficult airway scoring systems have been developed to aid clinicians in detecting and managing the difficult airway.

The most frequently used system of pre-intubation airway assessment in the OR is the Mallampati classification system (Figure 22-123).

This system assesses the tonsillar pillars and the uvula.

The more concealed they are, the more difficult the intubation will be.

Based on these features, the patient’s airway is grouped into four classes.

The higher the class, the more difficult the airway is expected to be.

Mallampati Class I: Entire tonsil clearly visible.

Mallampati Class II: Upper half of tonsil fossa visible.

Mallampati Class III: Soft and hard palate clearly visible.

Mallampati Class IV: Only hard palate visible.

The Mallampati assessment is done with the patient awake and sitting up.

The patient opens their mouth and sticks their tongue out.

Recognizing that the Mallampati system is of little use in unconscious patients, Cormack and LeHane adapted the system to classify the view one sees with a laryngoscope.

The Cormack and LeHane grading system is similar to Mallampati’s (Figure 22-123).

Cormack and LeHane Grade 1: Entire glottic opening and vocal cords visible.

Cormack and LeHane Grade 2: Epiglottis and posterior portion of glottic opening visible with a partial view of vocal cords.

Cormack and LeHane Grade 3: Only epiglottis and (sometimes) posterior cartilages visible.

Cormack and LeHane Grade 4: Neither epiglottis nor glottis visible.

A similar system used in EMS is the percentage of glottic opening (POGO) system.

The POGO scoring system scores the percentage of the glottis that can be visualized.

The score ranges from 0 (none of the glottis visualized) to 100 (vocal cords fully visualized).

This system also helps to predict the difficulty of endotracheal intubation (Figure 22-124).

As you might already have figured out, airway classification systems such as Mallampati, Cormack and LeHane, and POGO, though very helpful in more controlled or leisurely environments, have little application to emergency medicine.

This is especially so in the case of the austere prehospital environment where EMS practitioners would seldom have time to conduct one of these assessments.

However, knowing the features of these classification systems can help you to better anticipate the difficult airway.

The HEAVEN criteria (discussed later) were specifically developed to address these challenges and are a more appropriate system to use in the field.

LEMONS is an acronym that can be used to remember assessments and findings associated with a difficult airway.

Factors that have been assembled into the LEMONS mnemonic can encompass the entire difficult airway assessment, including bag-valve-mask ventilation, EGA insertion and ventilation, endotracheal intubation, and cricothyrotomy (Table 22-13).

LEMONS: Look externally, Evaluate 3-3-2 rule, Mallampati score, Obstruction, Neck mobility, Saturations.

Again, unfortunately, most of these clinical assessments cannot realistically be performed in the austere prehospital environment.

For example, the Mallampati score, as already described, relies on having a cooperative patient sit up, open their mouth, and stick out their tongue so the hard palate, uvula, and posterior pharynx can be visualized.

Astute EMS practitioners still look into the mouth before committing to intubation to assess overall working room—a modified Mallampati score.

Look externally: Look for factors that will make BVM ventilation, EGA, intubation, and surgical airway difficult.

They include facial hair, secretions, massive obesity, facial trauma, upper airway pathology, and gross face/neck anatomic deformities.

The 3-3-2 rule is one tool to help estimate the difficulty of laryngoscopy by assessing anatomic limitations to visualizing the larynx—for example, small mouth opening, short chin (no room to displace the tongue), and superior/anterior location (Figure 22-125).

Criteria evaluated are as follows (using the patient’s finger measurements): (1) Is mouth opening at least 3 fingers? (2) Is there room for 3 fingers between tip of chin and hyoid bone? (3) Is there room for 2 fingers between hyoid bone and top of thyroid cartilage?.

The Mallampati score assesses the working space available within the mouth (review Figure 22-123 and see Table 22-14).

To be done correctly, the patient must be able to sit up and stick out their tongue.

A crude estimate can be substituted by manually opening the mouth and looking, although this technique variation has never been validated.

A tongue blade can be used cautiously to avoid stimulating a gag reflex.

The most important thing is to make sure to look into the mouth to assess its opening, tongue size, dentures/dentition, edema, trauma, and secretions before committing to intubation.

A foreign body, the tongue, secretions, blood, vomitus, and/or edema can obstruct the airway.

Edema can result from trauma, infections such as epiglottitis and abscess, and allergic reactions.

Consider the patient’s age and history to predict possible obstruction.

Intubating a pediatric patient with retropharyngeal abscess or an adult with Ludwig’s angina is a scary proposition.

Neck mobility is most often limited by cervical spine immobilization although patients with rheumatoid arthritis or spinal fusions and elderly patients who have severe degenerative disease can also have restricted range of motion.

This is another reminder that any patient with spinal precautions should be considered to have a difficult airway.

It is important in these cases to remove the front of the cervical collar and apply manual stabilization with a jaw thrust during intubation to allow the chin to move forward.

One of the most critical elements in airway management involves the time available to successfully complete the procedure.

The primary time determinants are the ability to preoxygenate and create an oxygen reserve and the length of time an adequate oxygen saturation can be maintained, since saturation levels decrease while airway management procedures are being performed.

As noted earlier, a patient whose oxygen saturation is near 100 percent following preoxygenation has “adequate reserve,” above 90 percent but less than 100 percent has “limited reserve,” and less than 90 percent despite appropriate preoxygenation has “no reserve.” The HEAVEN criteria were developed to address an important weakness of LEMONS and the Mallampati scores, which were developed for the OR and are challenging or impossible to use in emergency patients who can be obtunded.

HEAVEN criteria were developed and validated in prehospital emergency patients.

They address both physiologic and anatomic factors that are easy to assess in the field (Table 22-15).

HEAVEN: Hypoxemia, Extremes of size, Anatomic challenges, Vomit/blood/fluid, Exsanguination, Neck motion (limited).

These criteria have been validated and shown to successfully predict first-pass success without hypoxia and with a poor laryngoscopic view.