Tracheal Intubation and Airway Management

1 What is the airway?

The airway is the conduit through which air and oxygen must pass before reaching the lungs. It includes the anatomic structures extending from the nose and mouth to the larynx and trachea.

2 What is airway management?

Airway management is the procedure for ensuring that the airway remains patent. It is the first step in the ABCs of basic resuscitation (B = breathing, C = circulation).

3 Why does airway management generally precede management of breathing and circulation?

If the airway is completely obstructed, no oxygen can reach the lungs, and the heart and circulation will have no oxygen to distribute to the body’s vital organs. However, the 2010 American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care now recommend beginning cardiopulmonary resuscitation with 30 chest compressions before delivering two rescue breaths. Although there is no proven mortality benefit to managing the airway after the circulation, the AHA rationale is that blood flow to vital organs depends on chest compressions.

Note: In addition, the AHA recommends “hands-only” chest compressions (i.e., no rescue breathing at all) for the untrained lay rescuer of a victim in cardiac arrest.

4 Describe the ways to manage the airway

The airway may remain patent without any intervention and can be managed with or without tracheal intubation. Airway management without intubation can involve a variety of maneuvers. In unconscious patients, the tongue commonly obstructs the airway. Techniques to open the airway include the head tilt–chin lift maneuver and the jaw thrust maneuver. Placement of oral or nasal airways may also help to maintain a patent airway. The use of a face mask with a bag-valve device (e.g., Ambu bag) is the usual next step in airway management. In the majority of patients, it is possible to maintain a patent airway without tracheal intubation. If tracheal intubation is required, it can be accomplished through surgical or nonsurgical techniques.

5 What are the indications for tracheal intubation?

There are five main indications:

6 Explain why upper airway obstruction is an indication for tracheal intubation

If the upper airway is obstructed and cannot be opened with the previously described maneuvers, the trachea must be intubated to avoid life-threatening hypoxemia. Although intubation will bypass the anatomic area of obstruction, the cause should be determined to evaluate appropriate timing of extubation or need for further treatment.

7 Explain how to evaluate hypoxemia as an indication for tracheal intubation

If the patient’s oxygen saturation is consistently less than 90% despite the use of high-flow oxygen delivered through a face mask, tracheal intubation should be considered. One hundred percent oxygen can be delivered reliably only with an endotracheal tube. Other factors to consider are the adequacy of cardiac output, blood hemoglobin concentration, presence of chronic hypoxemia, and reason for the hypoxemia. For example, patients with hypoxemia due to intracardiac right-to-left shunts may have chronic hypoxemia. In these patients, the administration of 100% oxygen with an endotracheal tube may not be effective in raising the oxygen saturation level.

8 Explain how to evaluate hypoventilation as an indication for tracheal intubation

With hypoventilation, the blood PCO₂ progressively rises, which also lowers the blood pH level (respiratory acidosis). With increasing CO₂ levels, patients eventually become unconscious (CO₂ narcosis). Low systemic pH may be associated with abnormal myocardial irritability and contractility. The exact level of pH or PCO₂ that requires assisted ventilation must be determined for each patient. Chronic respiratory acidosis (e.g., in a patient with severe chronic obstructive pulmonary disease) is usually better tolerated than acute respiratory acidosis.

9 Explain how to evaluate elevated work of breathing as an indication for tracheal intubation

Normally, the respiratory muscles account for less than 5% of the total body oxygen consumption. In patients with respiratory failure, this can increase to as much as 40%. It can be difficult to assess the work of breathing by clinical examination. However, patients who have rapid shallow breathing, use of accessory respiratory muscles, or paradoxic respirations have a predictably high work of breathing. The results of an arterial blood gas analysis (i.e., pH, PCO₂, and PO₂) may be initially normal in such patients. Eventually, the respiratory muscles fatigue and fail, causing inadequate oxygenation and ventilation. Mechanical ventilation can sometimes be done without tracheal intubation (see Chapter 9) but is more reliably accomplished with intubation.

10 Explain airway protection as an indication for tracheal intubation

In an awake patient, protective airway reflexes normally prevent the pulmonary aspiration of gastric contents. Patients with altered mental status from a variety of causes may lose these protective reflexes, increasing the risk of aspiration pneumonia. Tracheal intubation with a cuffed tube can decrease the risk of aspiration. However, liquids can still leak around the endotracheal tube cuff, and the glottic barrier is bypassed, which plays a role in bacterial colonization of the lower airways.

11 What are the surgical techniques for tracheal intubation?

Surgical techniques include cricothyroidotomy or tracheotomy, which involves placing an endotracheal tube directly into the trachea through the cricothyroid membrane or between two tracheal rings.

12 What are the commonly used nonsurgical techniques for tracheal intubation?

Nonsurgical techniques can be divided into techniques that incorporate direct vision and blind techniques. The most commonly used direct vision intubation technique is direct laryngoscopy. The laryngoscope is placed in the mouth and manipulated to expose the larynx. An endotracheal tube is then placed through the larynx into the trachea. Another direct vision technique uses the flexible fiberoptic bronchoscope. An endotracheal tube is loaded onto the bronchoscope, which is advanced through the larynx via the nose or mouth. Once the bronchoscope is in the trachea, the endotracheal tube is advanced into position. Blind intubation is generally performed through the nose because the nasopharynx guides the endotracheal tube toward the larynx. Some laryngoscopes incorporate a video screen to allow improved vision of glottic structures via a small camera at the tip of the laryngoscope blade.

13 Which drugs can be given to facilitate tracheal intubation?

Sedative or analgesic agents are given to reduce the discomfort of laryngoscopy and to blunt the hemodynamic response. Muscle relaxants can make direct laryngoscopy easier to perform. The main risks of sedative or analgesic drugs in this setting are hypotension and respiratory depression. The muscle relaxants cause paralysis of all skeletal muscle, including the respiratory muscles. If the trachea cannot be intubated, the patient may not resume spontaneous breathing if sedatives, analgesics, or muscle relaxants have been given.

14 What equipment should be prepared before direct laryngoscopy is attempted?

Before laryngoscopy is attempted, all equipment should be checked for proper function. This includes laryngoscope blades, laryngoscope handle, suction source, suction catheter, oxygen source, self-inflating bag or breathing circuit, face mask, oral airways, nasal airways, sedative agents, muscle relaxants, intravenous line, and patient monitors.

15 How is direct laryngoscopy accomplished?

The technique varies slightly depending on the type of blade used (Figs. 14-1 and 14-2). First, the head is placed in the sniffing position with cervical spine in flexion and atlantooccipital joint in extension. The blade is inserted into the right side of the mouth. Then the tongue is moved to the left. With a curved (Macintosh) blade, the tip is inserted between the base of the tongue and the superior surface of the epiglottis, an area called the vallecula. If a straight (Miller or Wisconsin) blade is used, the tip is manipulated to lift the epiglottis. With both blade types, once the tip is in position, the blade is moved forward and upward to expose the larynx. An endotracheal tube is then inserted into the trachea. Gentle downward pressure on the thyroid cartilage may help to improve the view of the larynx.

Figure 14-1 Two types of commonly used laryngoscope blades. The straight blade (left) is a size 3 Wisconsin blade. The curved blade (right) is a size 3 Macintosh blade.

Figure 14-2 Procedure for direct laryngoscopy. A, A curved laryngoscope blade is placed in the vallecula. Lifting the blade forward and upward exposes the larynx. B, A straight blade is used to lift the epiglottis directly and expose the larynx.

(From Gal TJ: Airway management. In Miller RD [ed]: Miller’s Anesthesia, 6th ed. New York, 2005, Churchill Livingstone, p 1634.)

16 What maneuver can be performed to minimize the risk of aspiration during direct laryngoscopy?

Cricoid pressure consists of firm manual pressure on the cricoid cartilage. This maneuver can occlude the esophagus and reduce the chance of gastric distention from mask ventilation. It can also prevent regurgitation of gastric contents into the pharynx. However, controversy exists about the effectiveness of this maneuver.

17 What is a difficult airway? What is a difficult intubation?

A difficult airway is a clinical situation in which an anesthesiologist or other specially trained clinician has difficulty with mask ventilation or tracheal intubation. Difficult intubation can be defined as one requiring more than three attempts at laryngoscopy or more than 10 minutes of laryngoscopy. Although the definitions are arbitrary, the inability to maintain a patent airway (with or without intubation) may be associated with anoxic brain injury and death.

18 How do you evaluate the airway for potential difficulty?

The history should address the ease of prior tracheal intubations. Patients who have general anesthesia for surgery frequently undergo tracheal intubation. The anesthetic record for the procedure should document the ease of intubation and the equipment used. On examination, one must evaluate four anatomic features: mouth opening, pharyngeal space, neck extension, and submandibular compliance.

19 How do you evaluate mouth opening and pharyngeal space to predict difficult intubation?

In the adult, a mouth opening of two to three fingerbreadths is usually adequate. One measure of pharyngeal space is the Mallampati class (Fig. 14-3). The patient is asked to sit upright with the head in a neutral position. Then he or she is asked to open the mouth as widely as possible and protrude the tongue as far as possible. The classification is based on the pharyngeal structures seen.

Figure 14-3 The Mallampati classification to evaluate pharyngeal space.

Intubation is generally easier in patients with class I airways than in patients with class IV airways. However, this test addresses only one of the four anatomic features required for easy direct laryngoscopy.

20 How do you evaluate neck extension and submandibular compliance to predict difficult intubation?

A normal adult has approximately 35 degrees of extension at the atlantooccipital joint. A decrease in extension may make it impossible to view the larynx with direct laryngoscopy. It can be difficult to assess the submandibular compliance by physical examination. Assessment of the mandibular space can be attempted by measuring the distance from the chin to the thyroid cartilage, the thyromental distance. An adult with less than 6.5 cm of thyromental distance may have a greater chance of difficult intubation than one with greater than 6.5 cm. Combining the various physical examination tests improves the ability to predict a difficult intubation, but no combination is foolproof.

21 How do you manage a potentially difficult intubation?

Three types of plans must be made when managing a difficult airway. The first is the primary approach to the intubation. The second is the plan for an emergency nonsurgical airway. Finally, a plan should exist for an emergency surgical airway (cricothyroidotomy or tracheotomy). Many factors affect the management plan for a potentially difficult airway. These factors include the indication for intubation, the urgency of the intubation, the availability of skilled personnel, and the availability of special equipment. Because an awake, cooperative, spontaneously breathing patient normally has a patent airway, an awake intubation may be the safest. Topical or local anesthetics can be used to decrease airway sensation and patient discomfort.

22 What are the ways to provide an emergency nonsurgical airway?

If tracheal intubation and mask ventilation are not possible and the airway is not patent, an emergency airway must be provided. The options for providing an emergency nonsurgical airway include laryngeal mask ventilation, transtracheal jet ventilation, or esophageal-tracheal Combitube ventilation. The laryngeal mask is the most widely available of the three options. It is inserted into the posterior pharynx and lies opposite the larynx. In elective situations, it has a success rate of more than 90%. It is less successful in emergencies, but its widespread availability makes it a valuable option in managing the difficult airway. Special versions of the laryngeal mask incorporate features designed to facilitate blind passage of an endotracheal tube into the trachea.

Note: Emergency intubations are associated with up to a 2% mortality because of the underlying conditions of the patient and the difficulties associated with the intubations. The risks are increased by performing direct laryngoscopy more than twice.

23 How is tracheal intubation confirmed?

Auscultation for bilateral breath sounds and absence of stomach inflation should be done after each intubation attempt. However, these signs may still be present with an esophageal intubation. Carbon dioxide capnography is one of the most reliable methods to confirm placement. The laryngoscopic view may be useful. If an experienced clinician clearly sees the tube between the vocal cords, this is definitive confirmation. The endotracheal tube itself commonly blocks sight of the vocal cords, and inexperienced clinicians may insert the tube in the esophagus despite having a good view of the larynx. Other confirmation methods include fiberoptic bronchoscopy or an esophageal detector device.

24 What are the immediate, short-term complications of tracheal intubation?

Immediate complications of intubation include dental injury, cervical spine injury, pharyngeal trauma, laryngeal injury, aspiration of gastric contents, and tracheal rupture. Nosebleed is a risk with nasal intubations. The most common injuries are minor lip trauma and dental injury.