Securing the airway is an important task for treating critically ill patients. Indications for endotracheal intubation include surgical procedure, respiratory failure, cardiac arrest, airway protection (ie, coma), and airway obstruction (ie, anaphylaxis, airway burns, airway bleeding).

For any patient undergoing surgery, preoperative assessment includes American Society of Anesthesiologists Classification (ASA) which assesses the physiologic status to predict operative risk.¹ ASA 1 is a normal healthy patient with good exercise tolerance.¹ ASA 2 is patient with mild systemic disease that is well controlled and no functional limitation.¹ ASA 3 is a patient with severe systemic disease that is not life threatening with some functional limitation.¹ ASA 4 is severe disease with a constant threat to life.¹ ASA 5 is a patient with is not going to survive without surgery.¹ ASA 6 is a brain dead patient for organ harvest.¹

For any patient requiring a secure airway, difficult intubation, defined as difficult facemask or supraglottic airway (SGA) ventilation, difficult supraglottic airway placement, difficult laryngoscopy, difficult tracheal intubation, or failed intubation attempts, should be anticipated.² Avoidance of “can’t intubate can’t oxygenate” situation or CICO is paramount. The ASA have released guidelines based on levels of evidence.² Recommendation for Category A has 3 levels: Level 1 has sufficient randomized control trials to conduct meta-analysis; Level 2 has multiple randomized control trials but not sufficient for meta-analysis; and Level 3 has a single randomized control trial.² Recommendation for Category B also has 4 levels: Level 1 has observational studies with clinical interventions for a specific outcome; Level 2 has observational studies with associative statistics; Level 3 has noncomparative observational studies with descriptive statistics; and Level 4 has case reports.² Based on the Fourth National Audit Project (4NAP), the following were associated with airway complications: human factors such as poor education and judgment; omission of airway assessment; poor planning; intubation failure managed with repeated attempts; obese patients; use of supraglottic devices on poor candidates such as obese patients or high risk for aspiration; delay for emergent front of neck airway; unrecognized esophageal intubation; failure to use capnography; and recovery events such as blood in airway, tracheal edema, or postobstructive pulmonary edema (POPE).^3-5 The Royal Academy of Anesthesiologists and Difficult Airway Society Guidelines are stratified into 4 plans.^6,7 Plan A is preparation, oxygenation, induction, mask ventilation, and intubation.^6,7 Plan B is rescue airway via supraglottic device.^6,7 Plan C is final attempt at preoxygenation via facemask ventilation.^6,7 Plan D is emergent front of neck airway or eFONA.^6,7 These societies advocate the Vortex Approach where a maximum of 3 attempts at oxygenation via supraglottic airway (SGA), facemask, or tracheal intubation.⁶ Further clinical deterioration or failure at all attempts mandates eFONA.⁷

Assessment

Initial airway assessment involves identifying patients who are difficult to ventilate or intubate. Factors associated with risk of difficult intubation include Mallampati class III or IV airway, inter-incisor distance of less than 3 cm, thyromental distance less than 6.5 cm, and decreased jaw or cervical spine range of motion.^2,7 A history of previous difficult intubations, previous head and neck surgery including decannulated tracheostomies, and radiation therapy should also be identified.^2,7 Factors associated with difficult bag-mask ventilation include facial hair, obesity, edentulous patients, advanced age, and obstructive sleep apnea. Scoring systems such as Mallampati and Cormack-Lehane should not be used alone but as adjunct to identify patients who are difficult to intubate (Fig. 13-1 and Table 13-1).^8-10 However, complete assessment is not always possible due to altered mental status and emergent need to secure the airway in the critical ill.

Preparation for Difficult Airway and Strategy for Intubation

The ASA, Royal Academy of Anesthesiologists, and Difficult Airway Society recommend having a preintubation strategy for intubation of a difficult airway.^2,6,7 The difficult airway algorithm from the ASA is shown in Figure 13-2, and it can be adapted to the individual situation. As with any medical emergency, calling for expert help and consultation early may avoid unnecessary harm to the patient.

Difficult airway cart should be available which should include endotracheal tubes of various sizes, laryngoscopes and blades with various sizes, emergent cricothyrotomy and tracheostomy kits, supraglottic devices, video assisted laryngoscopy, light wands and tube exchangers, straps to secure endotracheal tubes, and end-tidal CO₂ detectors. Strategies for intubation include: (1) awake intubation via fiberoptic (Category B3) or blind tracheal intubation, supraglottic devices, and optically guided intubation (Category B4); (2) video assisted laryngoscopy (Category A1); (3) intubating stylets or tube changers (Category B3) with possible complications of lung laceration and gastric perforation; (4) supraglottic devices such as laryngeal mask airway (LMA) with possible complications of bronchospasm, difficulty in swallowing, respiratory obstruction, laryngeal nerve injury, edema, and hypoglossal nerve paralysis (Category B4); (5) intubating laryngeal mask airway (iLMA) with possible complications of sore throat, hoarseness, and pharyngeal edema (Category B3); (7) (6) fiberoptic guided intubation (Category B3) and with Mallampati 3-4 Scores (Category A2), and lighted stylets or wands (Category B3)² (see Table 13-1).

The most common laryngoscope blades in clinical practice are the Macintosh and Miller laryngoscope blades. The Macintosh blade is curved, and the tip is placed in the vallecula and lifted up and out at a 45-degree angle. This should allow for visualization of the vocal cords. The Miller blade is straight and usually thinner than the Macintosh blade. It is used first to move the tongue to the side, at which point the epiglottis can be visualized. The blade is then used to lift the epiglottis and reveal the vocal cords.

Video laryngoscopy has emerged as a reliable tool for intubation with increased first-pass success, even by critical care fellows who are relatively inexperienced with intubation.^1,6,7 An intubating bougie or tube changer is a rubber coated, medium-stiff wire with a slanted tip. A laryngoscope is used to move the tongue out of the way to obtain the view seen by direct laryngoscopy. The bougie is advanced on the posterior aspect of the epiglottis toward the laryngeal opening. The laryngeal opening can be approximated if no structures can be visualized. Once through the glottic opening in the trachea, the slanted tip will catch on the tracheal rings. After “tactile confirmation,” an endotracheal tube is placed over the bougie and through the vocal cords.

Another technique in which the vocal cords are not directly visualized utilizes a lighted introducer or stylet. An endotracheal tube (ETT) with a stylet with a lighted tip is placed over the tongue, and the laryngeal opening is approximated. The light will make a particular midline circumscribed glow pattern when the stylet passes through the laryngeal opening into the trachea. An ETT can then be placed over the stylet. If the stylet enters the esophagus, the light will markedly dim.

Awake fiber-optic intubation remains the gold standard for management of a known difficult airway. It requires clinicians with advanced airway skills and other back-up plans in the event of complications. The procedure is a bit of a misnomer, as clinicians may use any combination of medications to relieve anxiety to facilitate the navigation of the bronchoscope loaded with an endotracheal tube past the vocal cords. The airway is prepared via antisialagogues such as glycopyrrolate, atropine, or hyoscine, but the associated tachycardia might make it a less-desirable option.¹¹ Local anesthetics such as lidocaine, 1.5 mg/kg topical 3 minutes before intubation, can blunt the hypertensive response, airway reactivity, and incidence of dysarrthmias.^12,13 Zofran maybe given to blunt the gag reflex.¹¹ Some still advocate for mild sedation, such as with ketamine, midazolam, dexmedetomidine, remifentanil, and propofol.^11,12 Regardless of the individual technique, the goal is for the patient to maintain spontaneous ventilation throughout so that, at any point, the procedure may be aborted safely without any undo harm to the patient. The patient is induced with general anesthesia once the endotracheal tube is advanced into the trachea, confirmed with both fiber-optic visualization and capnography. Complications include trauma to the airway and laryngospasm.

Preoxygenation

It is important to optimize the conditions for successful intubation. Preoxygenation of the patient replaces nitrogen in the functional residual capacity (FRC) in the lung with oxygen, creating a reservoir of oxygen to avoid hypoxemia during a period of apnea and intubation attempts. Three minutes of facemask oxygenation helps to maintain significantly higher oxygen saturation compared to 1-minute facemask oxygenation (Category A2). When compared to 4 maximal breaths in 30 seconds, results are equivocal; however, time to desaturation is longer with 3 minutes of preoxygenation with mask and 100% fraction of inspired oxygen (FIO₂).²

Positioning

Proper positioning is required to improve visualization of the larynx under direct laryngoscopy. The 3-airway axis model of laryngoscopy was originally described in 1944 by Bannister and Macbeth.^13,14 In order to visualize the larynx, the clinician must align the oral, pharyngeal, and laryngeal axes. Placing a pillow under the head or using an intubation ramp helps align the pharyngeal and laryngeal axes. Subsequent neck extension will align the oral axis, allowing visualization through all 3 axes. See Figure 13-2.

Patients with cervical spine instability, fractures, neuropathies, or radiculopathies may have additional morbidities if extension of the neck occurs. In-line neck stabilization with close attention to not extend the neck, as well as the use of video laryngoscopy may be useful techniques for visualizing the larynx without stressing the cervical spine.

Cricoid Pressure

Also known as the Sellick maneuver, this is a manual compression of the cricoid cartilage (C6) to prevent gastroesophageal reflux during intubation. The rationale for its use is debatable, since some studies have suggested that it does not decrease the risk for reflux. It also increases the risk of esophageal rupture if the patient vomits because 90% the esophagus is lateral to the trachea, and it may further occlude the trachea.

Rapid Sequence Intubation

Rapid sequence intubation (RSI) has been synonymous with the administration of an induction agent and neuromuscular blockade (NMB). The rationale is that it decreases the risk of aspiration and secures the airway rapidly. It consists of the 6 Ps, which are seen in Table 13-2. Preparation, or identifying the need for intubation, takes about 5 to 10 minutes.^13,15 Preoxygenation, or alveolar denitrogenation, creates a reservoir of oxygen and is performed via 100% nonrebreather (NRB) mask for 5 minutes. It avoids the need for ball-valve-mask ventilation and the risk of gastric aspiration. Premedication attenuates the physiologic response to intubation and provides sedation and analgesia. Paralysis has 2 components: induction medications and administration of NMBs. After the induction agent is given, the patient can be given either a depolarizing NMB or nondepolarizing NMB. After 45 seconds to 1 minute, the degree of paralysis is assessed via mandibular mobility. Neuromuscular blockade can be reversed by neostigmine, edrophonium, glycopyrrolate, atropine, or suggamex. The next P is Passage, which refers to the insertion of the endotracheal tube once paralysis is adequate. Visualization of the vocal cords may be improved by applying pressure on the thyroid. See Figure 13-3 for proper position or 3 airway axis model.