The incidence of a difficult laryngoscopy or intubation varies from 1.5% to 13%, and failed intubation has been identified as one of the anesthesia-related causes of death or permanent brain damage. In the management of UDTI, the anesthesia provider should follow the principles of the American Society of Anesthesiologists Difficult Airway Guidelines and prioritize the maintenance of ventilation and oxygenation, and seek additional resources including personnel (see Chapter 8).

The causes of UDTI have at their root the inability to position the patient adequately to align the oral, hypopharyngeal, and laryngeal axes as well as the inability to displace the tongue and other tissues of the hypopharynx to permit either direct line-of-sight visualization or visualization of the airway structures with a laryngoscope (direct, video, or otherwise). Prevalent causes of UDTI include initial improper patient positioning (especially with morbidly obese patients), large tongue relative to oral cavity, lingual tonsil hypertrophy, limited mouth opening, and limitations in neck extension (see Chapters 7 and 14).

When the laryngeal view is poor, use of a tracheal tube introducer with an angled distal tip can allow the anesthesia provider to negotiate a tracheal tube into the larynx and trachea without visualization. Tracheal tube introducers are commonly known as “bougies.” The technique was originally described by Sir Robert MacIntosh using a urinary “gum elastic bougie” and later popularized with the Eschmann tracheal tube introducer.

Passage of a bougie through the laryngeal inlet in cases of laryngeal pathology (distorted by swelling, infection, or tumor) is considerably more effective than with a tracheal tube due to its small diameter and intrinsic rigidity.

If face mask ventilation is adequate, a repeat attempt at optimized direct or video laryngoscopy with the plan to use bougie-aided intubation is a reasonable follow-up maneuver. An attempt is made to place the bougie into the larynx and trachea, with partial visualization (modified Cormack-Lehane grade IIb) or without visualization (grade III or IV). Blind insertion of the bougie into the larynx and trachea is possible if the angled tip of the bougie can be negotiated along the posterior surface of the epiglottis in the midline. Once the distal bougie is beyond site, noting markings on the shaft helps to keep the angulated tip oriented anteriorly. Entry of the bougie into the trachea is often accompanied with tactile feedback along the bougie’s shaft as its angulated tip passes over the cartilaginous rings and intermembranous spaces of the trachea, producing “clicks,” as it were. If clicks are not elicited, the bougie should be advanced gently to a maximum distance of 45 cm, or until distal holdup occurs, indicating contact with the narrowing bronchial tree. If clicks, holdup, or coughing (from tracheal irritation of the catheter) does not occur, it is likely that the bougie is not in the trachea, and thus is within the esophagus—removal of the bougie is warranted with a return to mask ventilation between each intubation attempt.