management of the difficult airway

Definitions:

A difficult airway is defined as the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation, or both (1).
Difficult face mask ventilation (1):

It is not possible for the anesthesiologist to provide adequate face mask ventilation due to one or more of the following problems: inadequate mask seal, excessive gas leak, or excessive resistance to the ingress or egress of gas.
Signs of inadequate face mask ventilation include (but are not limited to) absent or inadequate chest movement, absent or inadequate breath sounds, auscultatory signs of severe obstruction, cyanosis, gastric air entry or dilation, decreasing or inadequate oxygen saturation (SpO2), absent or inadequate exhaled carbon dioxide, absent or inadequate spirometric measures of exhaled gas flow, and hemodynamic changes associated with hypoxemia or hypercarbia (e.g., hypertension, tachycardia, arrhythmia).

Difficult laryngoscopy: it is not possible to visualize any portion of the vocal cords after multiple attempts at conventional laryngoscopy (1).
Difficult tracheal intubation: tracheal intubation requires multiple attempts, in the presence or absence of tracheal pathology (1).
Failed intubation: placement of the endotracheal tube fails after multiple intubation attempts (1).

Measurements: evaluation of the airway (1):

History: an airway history should be conducted, whenever feasible, prior to the initiation of anesthetic care and airway management in all patients. Examination of previous anesthetic records, if available in a timely manner, may yield useful information about airway management.
Physical examination: an airway physical examination should be conducted, whenever feasible, prior to the initiation of anesthetic care and airway management in all patients. Multiple airway features should be assessed.
Additional evaluation: additional evaluation may be indicated in some patients to characterize the likelihood or nature of the anticipated airway difficulty.

Treatment:

Rigid laryngoscope blades of alternate design and size from those routinely used; this may include a rigid fiberoptic laryngoscope.
Tracheal tubes of assorted sizes.
Tracheal tube guides. Examples include (but are not limited to) semirigid stylets, ventilating tube changer, light wands, and forceps designed to manipulate the distal portion of the tracheal tube.
Laryngeal mask airways of assorted sizes.
Flexible fiberoptic intubation equipment.
Retrograde intubation equipment.
At least one device suitable for emergency noninvasive airway ventilation (e.g., a hollow jet ventilation stylet or a transtracheal jet ventilator).
Equipment suitable for emergency invasive airway access (e.g., cricothyrotomy).
An exhaled CO2 detector.

Actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management.

An assessment of the likelihood and anticipated clinical impact of four basic problems that may occur alone or in combination: difficult ventilation, difficult intubation, difficulty with patient cooperation or consent, difficult tracheostomy.
A consideration of the relative clinical merits and feasibility of three basic management choices: awake intubation versus intubation after induction of general anesthesia; use of noninvasive techniques for the initial approach to intubation versus the use of invasive techniques (i.e., surgical or percutaneous tracheostomy or cricothyrotomy); preservation of spontaneous ventilation during intubation attempts versus ablation of spontaneous ventilation during intubation attempts.
The identification of a primary or preferred approach to awake intubation, the patient who can be adequately ventilated but is difficult to intubate, the life-threatening situation in which the patient cannot be ventilated or intubated.
The identification of alternative approaches that can be employed if the primary approach fails or is not feasible:

Techniques for difficult ventilation: intratracheal jet stylet; laryngeal mask airway; oral and nasopharyngeal airways; rigid ventilating bronchoscope; invasive airway access; transtracheal jet ventilation; two-person mask ventilation.
Techniques for difficult intubation: alternative laryngoscope blades; awake intubation; blind intubation (oral or nasal); fiberoptic intubation; intubating stylet or tube changer; laryngeal mask airway as an intubating conduit; light wand; retrograde intubation; invasive airway access.

There is no difference in the success rate of intubation and satisfaction of the anaesthetists and patients (with a mouth opening of >1.3 cm) in anticipated difficult nasal intubation with a videolaryngoscope versus fiberoptic intubation (2).

The uncooperative or pediatric patient may restrict the options for difficult airway management, particularly options that involve awake intubation.

A consideration of the relative merits of awake extubation versus extubation before the return of consciousness.
An evaluation for general clinical factors that may produce an adverse impact on ventilation after the patient has been extubated.
The formulation of an airway management plan that can be implemented if the patient is not able to maintain adequate ventilation after extubation.
A consideration of the short-term use of a device that can serve as a guide for expedited reintubation. This type of device is usually inserted through the lumen of the tracheal tube and into the trachea before the tracheal tube is removed. The device may be rigid to facilitate intubation and/or to facilitate ventilation.

References:

Practice guidelines for management of the difficult airway. An updated report by the American Society of Anesthesiologys task force on management of the difficult airway. Anesthesiology. 2003;98(5):1269-1277: full text | pdf.
A. Kramer et al. Fibreoptic vs videolaryngoscopic (C-MAC(R) D-BLADE) nasal awake intubation under local anaesthesia. Anaesthesia. 2015;70:400-406: full text | pdf.