Examination of the Upper Airway:
A focused examination of the airway is used to identify patients who are predicted to experience difficulties with traditional airway management procedures. These procedures commonly include BMV, placement of an extraglottic airway device (e.g., LMA™), or direct laryngoscopy and intubation.
Several clinical predictors of a difficult airway are described below. There is no single test that is both highly sensitive and specific in predicting difficulties. Based on the patient’s medical history and using a combination of clinical examinations, we are able to improve our ability to identify patients who will require special attention and equipment so as to provide them with safe airway management.
Difficult BMV is defined as the inability to provide adequate bag-mask ventilation and maintain oxygen saturation > 90%. The mnemonic “BONES” summarizes the common predictors of difficulty with BMV.
BONES:
Clinical Pearl: Difficult BMV: Remember the mnemonic “BONES”
Beard: A seal between the mask and the patient’s face is essential for effective BMV. Assuming the facemask is positioned properly, the most common reason for an incomplete mask seal is the presence of a beard. Less commonly, trauma, secretions, or facial abnormalities prevent an effective seal. If a seal cannot be created, positive pressure will result in oxygen leaking between the patient’s face and mask, and ventilation attempts will be ineffective.
Obesity: Obesity is associated with redundant oropharyngeal tissue. This may result in upper airway obstruction and difficulty with BMV in the unconscious patient.
No Teeth: Teeth provide a framework by creating a space between the tongue and palate. Without teeth, the tongue collapses against the palate when the mouth is closed, resulting in obstruction of oxygen flow with BMV. The use of an oropharyngeal airway, nasopharyngeal airway, or the patient’s dentures may be useful for BMV in the edentulous patient.
Elderly: Increased difficulty with BMV has been observed in patients > 55 years of age. This is thought to be due to a generalized decrease in the elasticity of the tissues and an increased incidence in obstructive and restrictive pulmonary disease.
Snoring & Stiffness: Snoring is a symptom of upper airway obstruction and is associated with obstructive sleep apnea (OSA) as well as difficulties with BMV. Diseases that reduce lung compliance (asthma, pulmonary edema, and fibrosis) are also associated with difficult BMV.
The Four Step Upper Airway Examination:
The Four Step Upper Airway Examination is used to assess several factors that may affect decisions concerning the patient’s airway management. This examination can usually be completed in less than a minute in the elective, awake, and cooperative patient. Modifications of the examination will be dictated by the patient’s condition (e.g., unconscious patient, C-spine collar).
Clinical Pearl:
Difficulty with bag-mask ventilation is not always associated with difficulties in placement of an extraglottic device (e.g., LMA™) or ETT. If difficulties with BMV occur, simple maneuvers, such as placement of an oropharyngeal airway, nasopharyngeal airway, or jaw thrust, may solve the problem. If difficulties persist, consider immediate placement of an extraglottic device or ETT.
1st Step: Assess Temporomandibular Joint Mobility
The first step of the test is to identify any restricted mobility of the temporomandibular joint (TMJ). Ask patients to sit up with their head in the neutral position and their mouth open as wide as possible. Note the mobility of the mandibular condyle at the TM joint. The condyle should rotate forward freely so that the width of the space created between the tragus of the ear and the mandibular condyle is approximately the breadth of one finger.
2nd Step: Assess Mouth Opening and Assign Mallampati Classification
The aperture of an adult patient’s mouth should admit three fingers between the teeth. This corresponds to a distance of approximately 5 – 6 cm in an adult. If the opening is < 2 finger breadths (< 2.5 cm), it will be difficult to insert the laryngoscope blade, let alone visualize the larynx. Note any loose, capped, prominent, or missing teeth as well as any dentures or dental bridge appliances.
Mallampati Classification:
Mallampati et al. first correlated the ability to visualize the oropharyngeal structures with the ease of tracheal intubation with a direct laryngoscope. Their classification was later modified by Samsoon and Young to include four classes. To assign a “modified” Mallampati classification, the examiner should face the patient at eye level. The oropharyngeal structures are classified with the patient sitting upright, head in the neutral position, mouth opened as wide as possible, and tongue maximally protruded without phonating (Fig. 6.1). The structures to visualize include: the pharyngeal arches, uvula, soft palate, hard palate, tonsillar beds, and posterior pharyngeal wall. Technical difficulties with tracheal intubation may be anticipated when only the tongue and soft palate are visualized in a patient during this maneuver. The anticipated difficulty of intubation with direct laryngoscopy increases in relation to the increase in the oropharyngeal class number. For patients with a class I oropharyngeal view, adequate exposure of the glottis during direct laryngoscopy should be easily achieved.
Using this classification, we can predict that the trachea of a patient with a class 4 hypopharynx, a full set of teeth, a restricted thyromental distance, and restricted atlantooccipital extension will be difficult to intubate using direct laryngoscopy. Patients who have a restricted airway may require techniques other than direct laryngoscopy to secure an airway. Choosing regional or local anesthesia rather than general anesthesia is one way to avoid the need for tracheal intubation. Other airway management options include “awake” intubation with topical anesthesia, intravenous conscious sedation, or the use of a laryngeal mask rather than an endotracheal tube.
Fig. 6.2 Modified mallampati classification of pharyngeal structures. Note that the soft palate is visible in Class III but not Class IV. (From Samsoon G, Young J. Anaesthesia 1987;42:487-490).
Fig. 6.3 Thyromental distance.
3rd Step: Assess Thyromental Distance and Mandibular Protrusion
The third step of this test is to assess the characteristics of the patient’s mandible, which involves evaluating the thyromental distance (TMD) and the patient’s ability to protrude the mandible.
The TMD is measured with the neck (atlantooccipital junction) in full extension. In adults, the distance from the lower border of the chin (mentum) to the thyroid cartilage notch should be ≥ 3 finger breadths (or > 6.5 cm). Distances of < 6.5 cm may be associated with an anterior larynx or a small mandible. A TMD < 6.5 cm would predict difficulty in exposing the larynx with a classic Macintosh laryngoscope.
Mandibular protrusion is evaluated by asking patients to bring their lower jaw as far forward as possible or to try to bite their upper lip with their bottom teeth. With Class I, the patient is able to protrude the lower incisors anterior to the upper