Airway Management in the Intensive Care Unit

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Chapter 34 Airway Management in the Intensive Care Unit*

The decision to instrument the airway of a patient is one of the most crucial taken; this approach to airway management, although often required in an emergency situation, requires considerable skill, experience, and knowledge of the different types of procedures available. The main reasons to instrument the airway are (1) failure of oxygenation, (2) failure of ventilation, and (3) protection of the airways.

Patients with a variety of medical and surgical diseases may require ventilatory assistance or improved airway control. Such patients include those with primary respiratory failure or with respiratory insufficiency secondary to other pathologic conditions. Implementation of respiratory support may be undertaken semielectively or on an emergency basis.

Airway instrumentation should be performed only by a skilled physician who has assessed the patient thoroughly addressing the risks and benefits for that patient. A vital step in this assessment is prediction of the ease with which intubation is likely to be possible, with identification of an appropriate alternative approach to use in case difficulties arise. An important point to remember is that patients die not because of a failure to intubate but as a result of failure to oxygenate; therefore, recurrent failed attempts to gain airway control should be avoided. Problems with ventilation can quickly lead to severe hypoxia, brain damage, or death.

Airway Assessment

Before instrumentation of the patient’s airway, a thorough assessment should be performed to ascertain the likelihood of difficulty in achieving airway control. Several specific aspects of this assessment are considered next.

Predictors of Difficult Intubation

Difficult intubation is common in the ICU population, with frequency of reported difficulty between 6.6% and 22%. A history of airway problems should be sought—for example, snoring, sleep apnea, congenital diseases (such as Down or Pierre-Robin syndrome), and previous anesthetic problems.

Examination of the patient should determine the following: ability to protrude the mandible, range of neck movement, atlantooccipital flexion and extension, interincisor distance (less than 3 cm indicates a high likelihood of difficulty), and modified Mallampati test (Figure 34-1). Other predictors of difficult intubation include thyromental distance of less than 7 cm (Patil’s test) and obesity. Further investigations when indicated could include the view of the larynx obtained at nasal endoscopy, which may predict the view at laryngoscopy; chest radiographs, which may show tracheal deviation or mediastinal masses; and CT scans, which may be useful when abnormal anatomy is suspected—for example, in association with tracheal stenosis.

Aspiration Risk

Aspiration of gastric contents can cause significant morbidity and mortality. Evidence suggests that reducing gastric volume and increasing pH of gastric contents will limit the risk of disorders associated with aspiration. Acid aspiration may lead to a chemical pneumonitis, but aspiration of food particles can result in physical obstruction of the bronchial tree with secondary bacterial pneumonia (Box 34-1 and Table 34-1).

Table 34-1 Drugs to Reduce Aspiration Risk

Drug Class Specific Agent Mechanism of Action
Histamine H2 receptor antagonists Ranitidine 50 mg IV Increases pH and decreases gastric volume
Proton pump inhibitors Omeprazole 40 mg IV Irreversibly binds H+/K+-ATPase; increases pH and decreases gastric volume
Nonparticulate antacids 0.3 M sodium citrate, 10 mL Neutralizes gastric pH but increases volume
Very effective at increasing gastric pH if given within 30 minutes
Prokinetics Metoclopramide 10 mg Reduces gastric volume

Endotracheal Intubation with Muscle Relaxation

Equipment

The most common laryngoscope blade used for intubation in adults is the curved Macintosh blade (Figure 34-4). This is inserted into the right side of the mouth to displace the tongue laterally. The tip of the blade sits in the vallecula and is lifted forward to elevate the epiglottis and expose the laryngeal inlet. The McCoy blade is a variant of the Macintosh and has a hinged tip to further lift the epiglottis. A straight Miller blade can be useful in adults in whom the epiglottis is difficult to displace. This blade is inserted further to directly lift the epiglottis. Where laryngoscopy may be difficult a video laryngoscope can be used. There are now a variety of different models available on the market (Figure 34-5). They require less manipulation of the cervical spine and allow intubation in a seated position, reducing the aspiration risk (Videos 1-4). image Awake fiberoptic intubation may be used were visualization of the larynx may be difficult by other means or if access to the mouth is restricted.

Laryngeal Anatomy

The view of the laryngeal inlet obtained at direct laryngoscopy can be graded in accordance with the Cormack and Lehane classification (Figure 34-6). Grade I and grade II views indicate straightforward intubation. A grade III view frequently necessitates the use of a gum elastic bougee to “railroad” the endotracheal tube (ETT) into position, whereas a grade IV view often will mandate a different strategy to achieve successful intubation.

Laryngeal Mask Airway

The laryngeal mask is a supraglottic device that has revolutionized anesthesia in the past 25 years. It is inserted orally and when inflated sits in the posterior hypopharynx, pushing the tongue base anteriorly and keeping the glottis open. Its design has been modified and improved over time. Using the laryngeal mask airway (LMA) to ventilate a paralyzed patient in the operating room is now considered acceptable, particularly since the advent of such masks with a gastric port to allow venting of any refluxed gastric secretion. The use of LMAs in resuscitation is promoted in certain practice areas owing to its ease of insertion.

The LMA is extremely useful in clinical situations in which mask ventilation would be difficult or when intubation is impossible. It can be used to maintain oxygenation while a plan for definitive airway control is made, or it can be used as a conduit for access to the larynx. A fiberoptic scope can be inserted through the LMA and an ETT passed over the scope into the trachea. The intubating LMA is specifically designed to facilitate tracheal intubation; special features include an epiglottic elevating bar facilitating access to the trachea. It can be useful in patients in whom neck movement is limited (Figure 34-8).

surgical airways

Cricothyroidotomy

In situations in which it is not possible to either intubate or ventilate the patient, an emergency cricothyroidotomy should be performed (Figure 34-9). The cricothyroid membrane is an avascular membrane joining the thyroid cartilage to the cricoid cartilage. A purpose made kink-resistant cannula can be inserted through the cricothyroid membrane into the trachea, and then the patient is jet ventilated through this tube. Larger cricothyroidotomy devices can be used that allow the patient to be ventilated in a conventional fashion. Surgical cricothyroidotomy requires more skill and involves dissection down to the cricothyroid membrane, followed by insertion of an appropriately sized endotracheal tube (6-mm inner diameter) into the trachea. Cricothyroidotomy is associated with multiple complications, including airway loss, esophageal trauma, bleeding, false passage formation, pneumothorax, and surgical emphysema.

Controversies and Pitfalls in Airway Management

The rapid sequence induction technique with application of cricoid pressure is a relatively recent introduction to anesthesia. It is widely adhered to in many countries (e.g., the United Kingdom) for cases in which aspiration of stomach contents is a risk during induction. Many countries, however, do not use cricoid pressure to help prevent aspiration (e.g., France). No agreement has emerged regarding which approach is safer. This lack of uniformity worldwide is set to be complicated by the advent of newer drugs. Suggamadex is a gamma cyclodextrin that directly binds aminosteroidal nondepolarizing muscle relaxants in the plasma. Suggamadex allows the rapid reversal of rocuronium-induced muscle relaxation and deep levels of blockade. This may make suxamethonium redundant in anesthesia, since it is used because of its rapid onset, and more important, rapid offset of effects. Suxamethonium also has a considerably worse side effect profile than does rocuronium.

Thiopental has been superseded in most countries by propofol as an induction agent, particularly because of its smoother postoperative profile. Thiopental is retained for rapid-sequence inductions by some operators, however, because of not only its rapid and predictable onset, with a definite end point, but also its rapid offset (generally 5 minutes)—a boon in failed intubation scenarios. In a classic rapid sequence induction, opioids should not be given before the trachea is intubated, mainly because of the increased time to return of spontaneous respiration, which may be dangerous with failure of intubation. Nevertheless, use of these agents is advocated in cases in which a large degree of cardiac stability is needed.