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A difficult airway exists in a patient when conventional face mask ventilation is problematic or tracheal intubation is difficult, requiring advanced airway skills for success. Patient factors such as micrognathia, a short neck, a large tongue, craniofacial abnormalities, pregnancy, and obesity are chronic conditions associated with a difficult airway but do not inherently define a difficult airway. Other conditions such as angioedema, epiglottitis, Ludwig's angina, retropharyngeal abscess, tracheal trauma, traumatic/expanding neck hematoma, and cervical trauma are examples of acute factors that similarly may cause a difficult airway condition to exist. When patients with any of these conditions develop dyspnea or respiratory distress, immediate action is required to avert life-threatening decompensation or permanent debility. Furthermore, these patients can present at any time: a patient with a penetrating neck injury may present to an ED without warning, or a long-term ICU patient with diffuse soft tissue edema and a beard may unexpectedly decompensate and require intubation. Therefore, in a variety of settings, clinicians must be prepared for rapid escalation of care and difficult airway management.

While either difficult bag–mask ventilation or difficult intubation occurs in approximately 5% of patients,13 a situation in which both bag–mask ventilation and intubation are difficult occurs concomitantly in much fewer patients.4 Of those, less than 1% of patients require a surgical airway for emergent management,5 a fraction likely due to advanced airway management skills of emergency physicians and intensivists, and further aided by the development of multiple tools for managing the difficult airway.

When new patients present in extremis, a detailed history is precluded. However, several historical factors portend a difficult airway and, if possible, should be rapidly determined:

  1. History of oral, neck, or cervical spine surgery or irradiation

  2. History of oral or neck tumor, cellulitis, or abscess

  3. History of neck or mandibular arthritis or other joint immobility

  4. Presentation as a result of oral, facial, neck, or cervical spine trauma

  5. Use of anticoagulants or presence of a coagulopathy

Likewise, a focused physical exam of the head and neck should be performed. The LEMON mnemonic can help direct the physical exam to determine if the patient might have a difficult airway6:

  1. Look externally and assess factors associated with a difficult airway: obesity, micrognathia, large tongue, long upper incisors, prominent overbite with protruding maxillary incisors or underbite with large mandibular incisors, short bull neck, poor dentition that could be dislodged into the airway, or evidence of trauma.

  2. Evaluate with the 3-3-2 rule. The 3-3-2 rules states that with the mouth open the patient should be able to insert three fingers between the teeth (the interincisor gap or, for edentulous patients, the “intergingival gap”; Figure 2-1), has three finger breadths between the front of the chin and hyoid bone (the “hyomental distance”; Figure 2-2), and has two finger breadths between the hyoid bone and the thyroid cartilage (the “thyrohyoid distance”; Figure ...

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