Critical care staff members require an understanding of structure and function in order to successfully manage the airway and the conditions that may affect it. The relevant information can be gained from a variety of sources.1–5 The airway begins at the nose and oral cavity and continues as the pharynx and larynx, which lead to the trachea (beginning at the lower edge of the cricoid cartilage) and then the bronchial tree. The airway¹ provides a pathway for airflow between the atmosphere and the lungs;² facilitates filtering, humidification, and heating of ambient air before it reaches the lower airway;³ prevents nongaseous material from entering the lower airway;⁶ and allows phonation by controlling the flow of air through the larynx and oropharynx.⁴

The larynx prevents food and other foreign bodies from entering the trachea. Reflex closure of the glottic inlet occurs during swallowing ⁶ and periods of increased intrathoracic (e.g., coughing, sneezing) or intra-abdominal (e.g., vomiting, micturition) pressure. In unconscious patients, these reflexes are lost, so glottic closure may not occur, increasing the risk of pulmonary aspiration.

Assessing Adequacy of the Airway

Adequacy of the airway should be considered in four aspects:

• Patency. Partial or complete obstruction will compromise ventilation of the lungs and likewise gas exchange.

• Protective reflexes. These reflexes help maintain patency and prevent aspiration of material into the lower airways.

• Inspired oxygen concentration. Gas entering the pulmonary alveoli must have an appropriate oxygen concentration.

• Respiratory drive. A patent, secure airway is of little benefit without the movement of gas between the atmosphere and the pulmonary alveoli effected through the processes of inspiration and expiration.

Patency

Airway obstruction most frequently is due to reduced muscle tone, allowing the tongue to fall backward against the postpharyngeal wall, thereby blocking the airway. Loss of patency by this mechanism often occurs in an obtunded or anesthetized patient lying supine. Other causes include the presence of blood, mucus, vomitus, or a foreign body in the lumen of the airway or edema, inflammation, swelling, or enlargement of the tissues lining or adjacent to the airway.

Upper airway obstruction has a characteristic presentation in the spontaneously breathing patient: noisy inspiration (stridor), poor expired airflow, intercostal retraction, increased respiratory distress, and paradoxical rocking movements of the thorax and abdomen.⁹ These resolve quickly if the obstruction is removed. In total airway obstruction, sounds of breathing are absent entirely, owing to complete lack of airflow through the larynx. Airway obstruction may occur in patients with an endotracheal tube (ET) or tracheostomy tube in situ due to mucous plugging or kinking of the tube or the patient’s biting down on a tube placed orally. If such patients are spontaneously breathing, they will have the same symptoms and signs just described. Patients on assisted (positive-pressure) breathing modes will have high inflation pressures, decreased tidal and minute volumes, increased end-tidal carbon dioxide levels, and decreased arterial oxygen saturation.

Protective Reflexes

The upper airway shares a common pathway with the upper gastrointestinal tract.⁶ Protective reflexes, which exist to safeguard airway patency and to prevent foreign material from entering the lower respiratory tract, involve the epiglottis, the vocal cords, and the sensory supply to the pharynx and larynx.¹⁰ Patients who can swallow normally have intact airway reflexes, and normal speech makes absence of such reflexes unlikely. Patients with a decreased level of consciousness (LOC) should be assumed to have inadequate protective reflexes.

Inspired Oxygen Concentration

Oxygen demand is elevated by the increased work of breathing associated with respiratory distress ¹¹ and by the increased metabolic demands in critically ill or injured patients. Often, higher inspired oxygen concentrations are required to satisfy tissue oxygen demand and to prevent critical desaturations during maneuvers for managing the airway. A cuffed ET, connected to a supply of oxygen, is a sealed system in which the delivered oxygen concentration also is the inspired concentration. A patient wearing a facemask, however, inspires gas from the mask and surrounding ambient air. Because the patient will generate an initial inspiratory flow in the region of 30 to 60 L per minute, and the fresh gas flow to a mask is on the order of 5 to 15 L per minute, much of the tidal inspiration will be “room air” entrained from around the mask. The entrained room air is likely to dilute the concentration of oxygen inspired to less than 50%, even when 100% oxygen is delivered to the mask.¹² This unwelcome reduction in inspired oxygen concentration can be mitigated by (1) using a mask with a reservoir bag, (2) ensuring that the mask is fitted firmly to the patient’s face, (3) using a high rate of oxygen flow to the mask (15 L per minute), and (4) supplying a higher oxygen concentration if not already using 100%.

Respiratory Drive

A patent, protected airway will not produce adequate oxygenation or excretion of carbon dioxide without adequate respiratory drive. Changing arterial carbon dioxide tension (PCO₂), by changing H⁺ concentration in cerebrospinal fluid (CSF), stimulates the respiratory center, which in turn controls minute volume and therefore arterial PCO₂ (negative feedback).11,13 This assumes that increased respiratory drive can produce an increase in minute ventilation (increased respiratory rate or tidal volume, or both, per breath), which may not occur if respiratory mechanics are disturbed. Brain injury and drugs such as opioids, sedatives, and alcohol are direct-acting respiratory center depressants.

Ventilation can be assessed qualitatively by looking, listening, and feeling. In a spontaneously breathing patient, listening to (and feeling) air movement while looking at the extent, nature, and frequency of thoracic movement will give an impression of ventilation. These parameters may be misleading, however. Objective assessment of minute ventilation requires PCO₂ measurement in arterial blood or monitoring of end-tidal carbon dioxide, which can be used as a real-time measure of the adequacy of minute ventilation.¹³ If respiratory drive or minute ventilation is inadequate, positive-pressure respiratory support may be required, and any underlying factors should be addressed if possible (e.g., depressant effect of sedatives or analgesics).

Management of the Airway

The aims of airway management are to provide an adequate inspired oxygen concentration; to establish a patent, secure airway; and to support ventilation if required.

Providing an Adequate Inspired Oxygen Concentration

Although oxygen can be administered via nasal cannula, this method does not ensure delivery of more than 30% to 40% oxygen (at most). Other disadvantages include lack of humidification of gases, patient discomfort with use of flow rates greater than 4 to 6 L per minute, and predisposition to nasal mucosal irritation and potential bleeding.¹⁴ Therefore, despite being more intrusive for patients, facemasks are superior for oxygen administration. The three main types of facemasks are shown in Figure 2.1:

Figure 2.1 Facemasks: anesthesia mask (A); simple facemask (B1); simple facemask with reservoir bag (B2); Venturi mask (C).

• The anesthesia-type facemask (mask A in Fig. 2.1) is a solid mask (with no vents) with a cushioned collar to provide a good seal. It is suitable for providing very high oxygen concentrations (approaching 100%) because entrainment is minimized and the anesthetic circuit normally includes a reservoir of gas. These masks become unacceptable for many awake patients within a few minutes because of the association with heat, moisture, and claustrophobia.

• The simple facemask has vents that allow heat or humidity out but that also entrain room air. These masks have no seal and are relatively loose-fitting. Such masks may have a reservoir bag (approximately 500 mL) sitting inferior to the mask (B2 in Fig. 2.1), or may have no reservoir (B1 in Fig. 2.1). Using a simple facemask, without a reservoir bag, it is difficult to deliver an inspired oxygen concentration in excess of 50% even with tight application and 100% oxygen flow to the mask. Under the same conditions, a simple mask with a reservoir bag can produce an inspired oxygen concentration of about 80%.

• The Venturi mask (C in Fig. 2.1) has vents that entrain a known proportion of ambient air when a set flow of 100% oxygen passes through a Venturi device.¹⁴ Thus, the inspired oxygen concentration (usually 24% to 35%) is known.

Establishing a Patent and Secure Airway

Establishing a patent and secure airway can be achieved using simple airway maneuvers, further airway adjuncts, tracheal intubation, or a surgical airway.

Airway Maneuvers

Simple airway maneuvers involve appropriate positioning, opening the airway, and keeping it open using artificial airways if needed.

Positioning for Airway Management

In the absence of any concerns about cervical spine stability (e.g., with trauma, rheumatoid arthritis, or severe osteoporosis), raising the patient’s head slightly (5 to 10 cm) by means of a small pillow under the occiput can help in airway management. This adjustment extends the atlanto-occipital joint and moves the oral, pharyngeal, and laryngeal axes into better alignment, providing the best straight line to the glottis (“sniffing” position).15,16

Clearing the Airway

Acute airway obstruction in the obtunded patient often due to the tongue or extraneous material—liquid (saliva, blood, gastric contents) or solid (teeth, broken dentures, food)—in the pharynx. In the supine position, secretions usually are cleared under direct vision using a laryngoscope and a rigid suction catheter.¹⁷ In some cases, a flexible suction catheter, introduced through the nose and nasopharynx, may be the best means of clearing the airway. A finger sweep of the pharynx may be used to detect and remove larger solid material in unconscious patients without an intact gag reflex. During all airway interventions, if cervical spine instability cannot be ruled out, relative movement of the cervical vertebrae must be prevented—most often by manual inline immobilization.^17,18

Triple Airway Maneuver

The triple airway maneuver often is beneficial in obtunded patients if it is not contraindicated by concerns about cervical spine instability. As indicated by its name, this maneuver has three components: head tilt (neck extension), jaw thrust (pulling the mandible forward), and mouth opening.¹⁹ The operator stands behind and above the patient’s head. Then the maneuver is performed as follows:

• Extend the patient’s neck with the operator’s hands on both sides of the mandible.

• Elevate the mandible with the fingers of both hands, thereby lifting the base of the tongue away from the posterior pharyngeal wall.

• Open the mouth by pressing caudally on the anterior mandible with the thumbs or forefingers.

Artificial Airways

If the triple airway maneuver or any of its elements reduces airway obstruction, the benefit can be maintained for a prolonged period by introducing an artificial airway into the pharynx between the tongue and the posterior pharyngeal wall (Fig. 2.2).

Figure 2.2 Artificial airways: oropharyngeal airway (OPA); nasopharyngeal airway (NPA); laryngeal mask airway (LMA).

The oropharyngeal airway (OPA) is the most commonly used artificial airway. Simple to insert, it is used temporarily to help facilitate oxygenation or ventilation before tracheal intubation. The OPA should be inserted with the convex side toward the tongue and then rotated through 180 degrees. Care must be taken to avoid pushing the tongue posteriorly, thereby worsening the obstruction. The nasopharyngeal airway (NPA) has the same indications as for the OPA but significantly more contraindications ²⁰ (Box 2.1). It is better tolerated than the OPA, making it useful in semiconscious patients in whom the gag reflex is partially preserved. These artificial airways should be considered to be a temporary adjunct—to be replaced with a more secure airway if the patient fails to improve rapidly to the point at which an artificial airway no longer is needed. Such airways should not be used in association with prolonged positive-pressure ventilation.

Advanced Airway Adjuncts

Advanced airway adjuncts fill the gap between simple airway maneuvers and the insertion of a tracheal tube or surgical airway. These devices can be used to facilitate safe reliable airway management and manual ventilation in the prehospital or emergency resuscitation setting, often without expert medical presence.

The laryngeal mask airway (LMA) is a small latex mask mounted on a hollow plastic tube.21–26 It is placed “blindly” in the lower pharynx overlying the glottis. The inflatable cuff helps wedge the mask in the hypopharynx, sitting obliquely over the laryngeal inlet. Although the LMA produces a seal that will allow ventilation with gentle positive pressure, it does not definitively protect the airway from aspiration. Indications for use of the LMA in critical care are (1) as an alternative to other artificial airways, (2) the difficult airway, particularly the “can’t intubate–can’t ventilate” scenario, and (3) as a conduit for bronchoscopy. It is possible to pass a 6.0-mm ET through a standard LMA into the trachea, but the LMA must be left in situ. The intubating LMA (ILMA), which was developed specifically to aid intubation with a tracheal tube, has a shorter steel tube with a wider bore, a tighter curve, and a distal silicone laryngeal cuff.^27–30 A bar present near the laryngeal opening is designed to lift the epiglottis anteriorly. The ILMA allows the passage of a specially designed size 8.0 ET.

In recent years, many modified LMAs have reached clinical practice. They have been designed with the intention of promoting easier insertion, improving reliability of the laryngeal seal, and allowing safe gastric drainage of gastric fluid.

The Combitube (esophageal-tracheal double-lumen airway) is a combined esophageal obturator and tracheal tube, usually inserted blindly.31–35 Whether the “tracheal” lumen is placed in the trachea or esophagus, the Combitube will allow ventilation of the lungs and give partial protection against aspiration. The Combitube also is a potential adjunct in the “cannot intubate–cannot ventilate” situation. Disadvantages include the inability to suction the trachea when the device is sitting in its most common position (in the esophagus). Insertion also may cause trauma, and the Combitube is contraindicated in patients with known esophageal disease or injury or intact laryngeal reflexes and in persons who have ingested caustic substances.

Tracheal Intubation

If the foregoing interventions are not effective or are contraindicated, tracheal intubation is required. This modality will provide (1) a secure, potentially long-term airway; (2) a safe route to deliver positive-pressure ventilation if required; and (3) significant protection against pulmonary aspiration. Orotracheal intubation is the most widely used technique for clinicians practiced in direct laryngoscopy (indications and contraindications in Box 2.2). Normally, anesthesia with or without neuromuscular blockade is necessary for this procedure, which is summarized in Box 2.3.

Box 2.3 Procedure

Orotracheal Intubation

• Position patient and induce anesthesia ± neuromuscular blockade (if needed).

• Perform manual ventilation using triple airway maneuver and oropharyngeal airway

• Hold laryngoscope handle (left hand) near the junction with blade.

• Insert the blade along the right side of the tongue—moving tongue to the left.

• Advance tip of the blade in the midline between tongue and epiglottis.

• Pull upward and along the line of the handle of the laryngoscope.

• Lift the epiglottis upward and visualize the vocal cords.

• Do not use the patient’s teeth as a fulcrum when attempting to visualize the glottis.

• Stop advancing tube when cuff is 2 to 3 cm beyond the cords.

• Connect to a bag-valve system and pressurize it by squeezing bag.

• Inflate cuff until audible leak around tube stops.

• Check correct tube position (auscultation) and assess cuff pressure.

• Check end-tidal CO₂ trace.

Tracheal intubation requires lack of patient awareness (as in the unconscious state or with general anesthesia) and the abolition of protective laryngeal and pharyngeal reflexes. The drugs commonly used to achieve these states are shown in Table 2.1. Anesthesia is achieved using an intravenous induction agent, although intravenous sedatives (e.g., midazolam) theoretically may be used. Opioids often are used in conjunction with induction agents because they may reduce the cardiovascular sequelae of laryngoscopy and intubation (tachycardia and hypertension) and may contribute to the patient’s unconsciousness.

Table 2.1

Drugs Used to Facilitate Tracheal Intubation

Drug	Dose (Intravenous)
Induction Agent
Propofol	1-2.5 mg/kg
Opioids
Fentanyl	1.0-1.5 µg/kg
Morphine	0.15 mg/kg
Nondepolarizing Agents
Atracurium	0.4-0.5 mg/kg
Vecuronium	0.1 mg/kg
Rocuronium	0.45-0.6 mg/kg
Depolarizing Agent
Succinylcholine (suxamethonium)	1.0-1.5 mg/kg

Abolition of protective laryngeal and pharyngeal reflexes sometimes is achieved by inducing a deep level of unconsciousness using one or more of the aforementioned agents, followed by inhalation of high concentrations of a volatile anesthetic agent (e.g., sevoflurane, isoflurane). This technique sometimes is used in the difficult airway scenario to obtain conditions suitable for tracheal intubation in a patient who is still breathing spontaneously.

More often, a muscle relaxant is used to abolish the protective reflexes, abduct the vocal cords, and facilitate tracheal intubation. In the elective situation, nondepolarizing neuromuscular blocking agents are used. These drugs have the disadvantage of requiring several minutes to exert their effect, during which the patient must receive ventilation via a mask, thus allowing the possibility of gastric dilation and pulmonary aspiration. In patients at high risk of the latter (e.g., nonfasting patients), a depolarizing muscle relaxant (succinylcholine) is used because it produces suitable conditions for intubation within 15 to 20 seconds, and mask ventilation is not required. Succinylcholine has several side effects—among them hyperkalemia, muscle pains, and (rarely) malignant hyperpyrexia.

Nasotracheal intubation shares the problems and contraindications associated with the NPA.²⁰ The technique usually is employed when there are relative contraindications to the oral route (e.g., anatomic abnormalities, cervical spine instability). Nasotracheal intubation may be achieved under direct vision or with use of a blind technique, either with the patient under general anesthesia or in the awake or lightly sedated patient with appropriate local anesthesia (Box 2.4). If orotracheal or nasotracheal intubation is required but cannot be achieved, then a surgical airway is required (see later).

Box 2.4 Procedure

Nasotracheal Intubation (Blind and Under Direct Vision)

Preparation and Assessment of the Patient

1. Use a nasal decongestant such as phenylephrine to reduce bleeding.

2. Provide local anesthesia to the nasal mucosa.

3. Examine each nostril for patency and deformity.

4. Choose the most patent nostril, and use an appropriate-size ET.

5. After induction of anesthesia, position the head and neck as for oral intubation.

ET, endotracheal tube.

With a need for isolation of one lung from another, a double-lumen tube (having one cuffed tracheal lumen and one cuffed bronchial lumen fused longitudinally) can be used.³⁶ The main indications are (1) to facilitate some pulmonary or thoracic surgical procedures; (2) to isolate a lung containing contaminated fluid (e.g., in lung abscess) or blood, thereby preventing contralateral spread; and (3) to enable differential or independent lung ventilation (ILV). ILV allows each lung to be treated separately—for example, to deliver positive-pressure ventilation with high positive end-expiratory pressure (PEEP) to one lung while applying low levels of continuous positive airway pressure (CPAP) only to the other. Such a strategy may be advantageous in cases of pulmonary air leak (bronchopleural fistula, bronchial tear, or severe lung trauma) or in severe unilateral lung disease requiring ventilatory support.^37,38

Providing Ventilatory Support

If a patient has no (or inadequate) spontaneous ventilation, then a means of generating gas flow to the lower respiratory tract must be provided. Negative pressure, mimicking the actions of the respiratory muscles, occasionally is used in some patients who require long-term ventilation. In acute care, however, ventilation is achieved using positive pressure, which requires an unobstructed airway; in the nonintubated patient, this is best achieved by proper positioning, the triple airway maneuver, and use of an OPA or NPA. In a patient without an ET in place, particularly if some degree of airway obstruction exists, positive-pressure ventilation often will cause gastric distention and (potentially) regurgitation and pulmonary aspiration.

Bag-Valve-Mask Ventilation

Ventilation with a mask requires an (almost) airtight fit between mask and face. This is best achieved by firmly pressing the mask against the patient’s face using the thumb and index finger (C-grip) while pulling the mandible upward toward the mask with the other three fingers. The other hand is used to squeeze the reservoir bag, generating positive pressure. Excessive pressure from the C-grip on the mask may lead to backward movement of the mandible with subsequent airway obstruction, or a tilt of the mask with leakage of gas. If a proper seal is difficult to attain, placing a hand on each side of the mask and mandible is advised, with a second person manually compressing the reservoir bag (four-handed ventilation). Bag-valve-mask systems have a self-reinflating bag, which springs back after compression, thereby drawing gas in through a port with a one-way valve. It is important to have a large reservoir bag with a continuous flow of oxygen attached to this port in order to ensure a high inspired oxygen concentration.39,40 Bag-valve-mask ventilation usually is a short-term measure in urgent situations or is used in preparation for tracheal intubation.

Prolonged Ventilation Using a Sealed Tube in the Trachea

Ventilation of the lungs with a bag-valve-mask arrangement is difficult if required for more than a few minutes or if the patient needs to be transported. In these instances, ventilation through a sealed tube in the trachea is indicated. Orotracheal or nasotracheal intubation, surgical cricothyrotomy, and tracheostomy all achieve the same result: a cuffed tube in the trachea, allowing the use of positive-pressure ventilation and protecting the lungs from aspiration. Mechanical ventilation is discussed in Chapter 9.

Apneic Oxygenation

Apneic oxygenation is achieved using a narrow catheter that sits in the trachea and carries a flow of 100% oxygen. The catheter may be passed into the trachea via an ET or under direct vision through the larynx. This apparatus can be set up as a low-flow open system (gas flow rate of 5 to 8 L per minute) or as a high-pressure (jet ventilation) system ⁴¹ and can be used to maintain oxygenation with a difficult airway either at intubation or at extubation (see later).

Physiologic Sequelae and Complications of Tracheal Intubation

Laryngoscopy is a noxious stimulus that, in an awake or lightly sedated patient, would provoke coughing, retching, or vomiting and laryngospasm. In clinical practice, however, laryngoscopy and tracheal intubation usually are performed after induction of anesthesia, and in emergency situations, the patient often is hypoxic and hypercarbic, with increased sympathetic nervous system activity. Thus, the physiologic effects of laryngoscopy and tracheal intubation tend to be masked.

Laryngoscopy and intubation cause an increase in circulating catecholamines and increased sympathetic nervous system activity, leading to hypertension and tachycardia. This represents an increase in myocardial work and myocardial oxygen demand, which may provoke cardiac dysrhythmias and myocardial hypoxia or ischemia. Laryngoscopy increases cerebral blood flow and intracranial pressure—particularly in patients who are hypoxic or hypercarbic at the time of intubation.⁴² This rise in intracranial pressure will be exaggerated if cerebral venous drainage is impeded by violent coughing, bucking, or breath-holding.

Coughing and laryngospasm occur frequently in patients undergoing laryngoscopy and intubation when muscle relaxation and anesthesia are inadequate. Increased bronchial smooth muscle tone, which increases airway resistance, may occur as a reflex response to laryngoscopy or may be due to the physical presence of the ET in the trachea; in its most severe form, termed bronchospasm, this increased tone causes audible wheeze and ventilatory difficulty. Increased resistance to gas flow will occur because the cross-sectional area of the ET is less than that of the airway. This difference usually is unimportant with positive-pressure ventilation but causes a significant increase in work of breathing in spontaneously breathing patients. Resistance is directly related to 1/r⁴ (where r is the radius of the ET) and will be minimized by use of a large-bore ET. Gas passing through an ET, bypassing the nasal cavity, also loses the beneficial effects of warming, humidification, and the addition of traces of nitric oxide (NO).⁴³

The effects of intubation on functional residual capacity (FRC) are complex. In patients under anesthesia, a fall in FRC is well documented. This decrease may be due to the loss of respiratory muscle tone following induction of anesthesia and the relatively unopposed effect of the elastic recoil in the lungs.⁴³ The increased resistance to gas flow due to the presence of the ET may slow expiration, producing intrinsic PEEP (and therefore an increase in FRC) if the next inspiration begins before expiration is complete.

Laryngoscopy and intubation may cause bruising, abrasion, laceration, bleeding, or displacement or dislocation of the structures in and near the airway (e.g., lips, teeth or dental prostheses, tongue, epiglottis, vocal cords, laryngeal cartilages). Dislodged structures such as teeth or dentures may be aspirated, blocking the airway more distally. Less common complications include perforation of the airway with the potential for the development of a retropharyngeal abscess or mediastinitis. Over time, erosions due to pressure and ischemia may develop on the lips or tongue (or external nares and anterior nose in patients with a nasotracheal tube) and in the larynx or upper trachea.⁴⁴ These lesions result in a breach of the mucosa with the potential for secondary infection. In the case of the lips and tongue, such lesions are (temporarily) disfiguring and painful and may inhibit attempts to talk or swallow.

The mucosa of the upper trachea (subglottic area) is subjected to the pressure of the cuff of the ET. This pressure reduces perfusion of the tracheal mucosa and, combined with the mechanical movement of the tube (from patient head movements, nursing procedures, or rhythmic flexion with action of the ventilator), tends to cause mucosal damage and increase the risk of superficial infection. These processes may lead to ulceration of the tracheal mucosa, fibrous scarring, contraction, and ultimately stenosis, which can be a life-limiting or life-threatening problem. Although irrefutable evidence is lacking, most clinicians believe that limiting the period of orotracheal or nasotracheal intubation and reducing cuff pressures may reduce the frequency of this complication.⁴⁴

Any tube in the trachea has a significant effect on the mechanisms protecting the airway from aspiration and infection. The mucus escalator may be inhibited by mucosal injury and by the lack of warm humidified airflow over the respiratory epithelium.⁴⁵ The disruption of normal swallowing results in the pooling of saliva and other debris in the pharynx and larynx above the upper surface of the tube’s inflatable cuff, which may become the source of respiratory infection if the secretions become colonized with microorganisms, or may pass beyond the cuff into the lower airways—that is, pulmonary aspiration (silent or overt).^46,47 The former may occur as a result of (1) colonization of the gastric secretions and the regurgitation of this material up the esophagus to the pharynx or (2) transmission of microorganisms from the health care environment to the pharynx via medical equipment or the hands of hospital staff or visitors (cross-infection).^45,47–50

The presence of a tube traversing the larynx and sealing the trachea makes phonation impossible. The implications of this limitation for patients and their families often are ignored. If patients cannot tell caregivers about pain, nausea, or other concerns, they may become frustrated, agitated, or violent. This may result in the excessive use of sedative or psychoactive drugs, which prolong time on ventilation and stay in the intensive care unit (ICU), with the risk of infection increased accordingly.⁵¹ The inability to communicate may therefore be a real threat to patient survival. Potential solutions involve the use of letter and picture boards, “speaking valves” (with tracheostomy), laryngeal microphones, or computer-based communication packages. The involvement and innovations of disciplines such as the speech and language center may be advantageous.

The Difficult Airway

The difficult airway has been defined as “the clinical situation in which a conventionally trained anesthetist experiences difficulty with mask ventilation of the upper airway, tracheal intubation, or both.”⁵² It has been a commonly documented cause of adverse events including airway injury, hypoxic brain injury, and death under anesthesia.^53–59 The frequency of difficulty with mask ventilation has been estimated to be between 1.4% and 7.8%,^60–62 while tracheal intubation using direct laryngoscopy is difficult in 1.5% to 8.5% and impossible in up to 0.5% of general anesthetics.^58,63 The incidence of failed intubation is approximately 1 : 2000 in the nonobstetric population and 1 : 300 in the obstetric population.⁶⁴ In the critical care unit, up to 20% of all critical incidents are airway related,^65–67 and such incidents may occur at intubation, at extubation, or during the course of treatment (as with the acutely displaced or obstructed ET or tracheostomy tube).

Recognizing the Potentially Difficult Airway

Many conditions are associated with airway difficulty (Table 2.2), including anatomic abnormalities, which may result in an unusual appearance, thereby alerting the examiner. The goal is to identify the potentially difficult airway and develop a plan to secure it. Factors including age older than 55 years, body mass index greater than 26 kg/m², presence of a beard, lack of teeth, and a history of snoring have been identified as independent variables predicting difficulty with mask ventilation—in turn associated with difficult tracheal intubation.^61,68

Table 2.2

Conditions Associated with Difficult Airway

^*Visit http://www.erlanger.org/craniofacial and http://www.faces-cranio.org for specific details.

Data from Criswell JC, Parr MJA, Nolan JP: Emergency airway management in patients with cervical spine injuries. Anaesthesia 1994;49:900-903; and Morikawa S, Safar P, DeCarlo J: Influence of head position upon upper airway patency. Anaesthesiology 1961;22:265.

Mallampati ⁶⁹ developed a grading system (subsequently modified⁶⁴) that predicted ease of tracheal intubation at direct laryngoscopy. The predictive value of the Mallampati system has been shown to be limited^70,71 because many factors that have no influence on the Mallampati classification—mobility of head and neck, mandibular or maxillary development, dentition, compliance of neck structures, and body shape—can influence laryngeal view.^53,66,72,73 A study of a complex system including some of these factors found the rate of difficult intubation to be 1.5%, but with a false-positive rate of 12%.⁷⁴ A risk index based on the Mallampati classification, a history of difficult intubation, and five other variables lacked sufficient sensitivity and specificity.⁷⁵ Airway management should be based on the fact that the difficult airway cannot be reliably predicted.^76,77 This is a particularly important consideration in the critical care environment.

The Obstructed Airway

Although the most common reason for an obstructed airway in the unintubated patient is posterior displacement of the tongue in association with a depressed level of consciousness, it is the less common causes that provide the greatest challenges. It is important to elucidate the level at which the obstruction occurs and the nature of the obstructing lesion. Obstruction may be due to infection or edema (epiglottitis, pharyngeal or tonsillar abscess, mediastinal abscess), neoplasm (primary malignant or benign tumor, metastastic spread, direct extension from nearby structures), thyroid enlargement, vascular lesions, trauma, or foreign body or impacted food.14,78

Airway lesions above the level of the vocal cords are considered to lie in the upper airway and commonly manifest with stridor.⁷⁹ If breathing is labored and associated with difficulty breathing at night, rather than just noisy breathing, then the narrowing probably is more than 50%. Patients with these lesions usually fall into one of two groups: (1) those who can be intubated, usually under inhalational induction, with the ENT (ear-nose-throat) surgeon immediately available to perform rigid bronchoscopy or tracheostomy if required, or (2) those who require a tracheostomy performed while under local anesthesia. In patients with midtracheal obstruction, computed tomography (CT) imaging usually is necessary to discover the exact level and nature of the obstruction and to allow planning of airway management for nonemergency clinical presentations.⁷⁹ Tracheostomy often is not beneficial because the tube may not be long enough to bypass the obstruction. In such instances, fiberoptic intubation often may be useful.⁷⁹ Lower tracheal obstruction often is due to space-occupying lesions in the mediastinum and necessitates multidisciplinary planning involving ENT, cardiothoracic surgery, anesthesia, and critical care team members.

Trauma and the Airway

Airway management in the trauma victim provides additional challenges because the victim often has other life-threatening conditions and preparation time for management of the difficult airway is limited. Approximately 15% of severely injured patients have maxillofacial involvement, and 5% to 10% of patients with blunt trauma have an associated cervical spine injury (often associated with head injury).⁸⁰

Problems encountered in trauma patients include presence in the airway of debris or foreign bodies (e.g., teeth), vomitus, or regurgitated gastric contents; airway edema; tongue swelling; blood and bleeding; and fractures (maxilla and mandible). Patients must be assumed to have a full stomach (requiring bimanual cricoid pressure and a rapid-sequence induction for intubation), and many will have pulmonary aspiration before the airway is secured. An important consideration in most cases is the need to avoid movement of the cervical spine at laryngoscopy or intubation.17,18 Direct injury to the larynx is rare but may result in laryngeal disruption, producing progressive hoarseness and subcutaneous emphysema. Tracheal intubation, if attempted, requires great care and skill because it may cause further laryngeal disruption. With Le Fort fractures, airway obstruction or compromised respiration requiring immediate airway control is present in 25% of cases.⁸¹ Postoperative bleeding after operations to the neck (thyroid gland, carotid, larynx) may compress or displace the airway, leading to difficulty in intubation.

The Airway Practitioner and the Clinical Setting

Although airway difficulties often are due to anatomic factors as discussed, it is important to recognize that the inability to perform an airway maneuver also may be due to a practitioner’s inexperience or lack of skill.82–87 Expert opinion and clinical evidence also identify lack of skilled assistance as a factor in airway-related adverse events.^88–91 As might be expected, inexperience and lack of suitable help may contribute to failure in optimizing the conditions for laryngoscopy (Box 2.5). Airway and ventilatory management performed in the prehospital setting or in the hospital but outside an operating room (OR) carries a higher frequency of adverse events and a higher mortality rate when compared with those performed using anesthesia in an OR.^92–96 In the critical care unit, all invasive airway maneuvers are potentially difficult.⁹⁷ Positioning is more difficult on an ICU bed than on an OR table. The airway structures may be edematous after previous laryngoscopy or presence of an ET. Neck immobility, or the need to avoid movement in a potentially unstable cervical spine, may be other contributing factors.^98–100 Poor gas exchange in ICU patients reduces the effectiveness of preoxygenation and increases the risk of significant hypoxia before the airway is secured.¹⁰¹ Cardiovascular instability may produce hypotension or hypoperfusion, or may lead to misleading oximetry readings (including failure to record any value at all), a further confounding factor for the attending staff.^102,103

Box 2.5 Common Errors Compromising Successful Intubation

Poor patient positioning

Failure to ensure appropriate assistance

Faulty light source in laryngoscope or no alternative scope

Failure to use a longer blade in appropriate patients

Use of inappropriate tracheal tube (size or shape)

Lack of immediate availability of airway adjuncts

Managing the Difficult Airway

Management of the difficult airway can be considered in the framework of three possible clinical scenarios with progressively increasing risks for the patient: (1) the anticipated difficult airway; (2) the unanticipated difficult airway; and (3) the difficult airway resulting in a “cannot intubate/cannot ventilate” situation.

Requirements for clinicians involved in airway management include the following:

• Expertise in recognition and assessment of the potentially difficult airway. This involves the use of the assessment techniques noted previously and a “sixth sense.”⁷⁶

• The ability to formulate a plan (with alternatives).52,53,104–106

• Familiarity with algorithm(s) that outline a sequence of actions designed to maintain oxygenation, ventilation, and patient safety. The American Society of Anesthesiologists (ASA) guidelines ⁵² and the composite plan from the Difficult Airway Society (DAS)¹⁰⁴ are shown in Figures 2.3 and 2.4. The latter summarizes four airway plans (A to D), available from the DAS website (www.das.uk.com).

Figure 2.3 Algorithm for managing the difficult airway. (Adapted from Practice guidelines for management of the difficult airway: An updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anaesthesia 2003;98:1269.)

Figure 2.4 A four-component algorithm for managing the difficult airway. (From Difficult Airway Society: Difficult Airway Society Composite Plan. Anaesthesia 2004;59:675-694.)

• The skills and experience to use a number of airway adjuncts, particularly those relevant to the unanticipated difficult airway.

The Anticipated Difficult Airway

The anticipated difficult airway is the “least lethal” of the three scenarios—with time to consider strategy, optimize patient status, and obtain appropriate adjuncts and personnel. The key questions are as follows:

1. Should the patient be kept awake or be anesthetized for intubation?

2. Which technique should be used for intubation?

Awake Intubation

Awake intubation is more time-consuming, requires experienced personnel, is less pleasant for the patient (compared with intubation under anesthesia), and may have to be abandoned as a result of the patient’s inability or unwillingness to cooperate. Because spontaneous breathing and pharyngeal or laryngeal muscle tone is maintained, however, it is significantly safer. The techniques available are fiberoptic and retrograde intubation. It also may be used in patients judged to be at risk for a difficult airway, whereupon an initial direct laryngoscopic view allows intubation.

Fiberoptic Intubation.

Fiberoptic intubation is a technique in which a flexible endoscope with a tracheal tube loaded along its length is passed through the glottis. The tracheal tube is then pushed off the endoscope and into the trachea, and the endoscope is withdrawn. An informed patient, trained assistance, and adequate preparation time make fiberoptic intubation less stressful. The nasotracheal route is used most often and requires the use of nasal vasoconstrictors. Nebulized local anesthetic is delivered to the airway via facemask. Sedation may be given, but ideally the patient should remain breathing spontaneously and responsive to verbal commands. The procedure often is time-consuming and tends to be used in elective situations ¹⁰⁷ (Box 2.6).

Box 2.6 Indications for Fiberoptic Intubation

Anticipated difficult intubation

Avoidance of dental damage in high-risk patient

Direct laryngeal trauma

Other need for awake intubation

Retrograde Intubation.

For retrograde intubation,108,109 local anesthesia is provided and the cricothyroid membrane is punctured by a needle through which a wire or catheter is passed upward through the vocal cords. When it reaches the pharynx, the wire is visualized, brought out through the mouth, and then used to guide the ET through the vocal cords before it is withdrawn. This technique also can be used to guide a fiberoptic scope through the vocal cords. Owing to time constraints, it is not suitable for emergency airway access and is contraindicated in any patient with an expanding neck hematoma or coagulopathy.

Intubation Under Anesthesia

It may be decided, in spite of the safety advantage of awake intubation, to anesthetize the patient before attempted intubation. Preparation of the patient, equipment, and staff is paramount (Box 2.7). Adjuncts such as those described later should be available, either to improve the chances of intubation or to provide a safe alternative airway if intubation cannot be achieved.

Box 2.7 Checklist for Anticipated Difficult Intubation of Patient Under General Anesthesia

• Prepare and assess the patient.

• Prepare and test the equipment.

• Ensure skilled assistance with knowledge of BURP/bimanual laryngoscopy.

• Have available:

• A range of tracheal tubes lubricated and cuffs tested for patency (women: 7.0 to 7.5 mm in internal diameter; men: 7.5 to 9.0 mm in internal diameter).

• Endotracheal tube stylets

• Laryngeal mask airway (LMA)

• A range of laryngoscopes including specialized blades and handles

• Check battery and bulb function.

• Check functioning of suction devices.

• Use optimal patient position.

• Preoxygenation with 100% oxygen for 3 to 5 minutes if possible

• Provide other equipment as desired:

• Gum elastic bougie *

BURP, backward, upward, and rightward pressure.

^*Depending on choice of individual practitioner.

Unanticipated Airway Difficulty

The unanticipated difficult airway allows only a short period to solve the problem if significant hypoxemia, hypercarbia, and hemodynamic instability are to be avoided. The patient usually is anesthetized, may be apneic, and may have received muscle relaxants, and previous initial attempt(s) at intubation may have been unsuccessful. If appropriate equipment, assistance, and experience are not immediately at hand, little time is available to obtain them. Nevertheless, it is essential to maintain oxygenation and avoid hypercarbia if possible—commonly by mask ventilation with 100% oxygen. The four-handed technique often is used.

If the practitioner is inexperienced, if the patient has had no (or a relatively short-acting) muscle relaxant, and if ventilation is not a problem, it may be appropriate to let the patient recover consciousness. An awake intubation can then be planned either after a short period of recovery or on another occasion. With an experienced practitioner, it may be appropriate to continue, using techniques to improve the chances of visualizing and intubating the larynx. As discussed next, various adjuncts may be useful in this situation and also in the anticipated difficult airway when it has been decided to intubate with the patient under anesthesia.

Bimanual Laryngoscopy

Application of pressure on the cricoid area or the upper anterior tracheal wall, or both, by the laryngoscopist (a technique sometimes termed bimanual laryngoscopy) may improve laryngeal view.110,111 When the view is optimized, an assistant maintains the pressure and thus the position of the larynx, freeing the hand of the laryngoscopist to perform the intubation. The use of “blind” cricoid pressure, or BURP (backward, upward, and rightward pressure), by an assistant may impair laryngeal visualization.^112–114

Stylet (“Introducer”) and Gum Elastic Bougie

The stylet is a smooth, malleable metal or plastic rod that is placed inside an ET to adjust the curvature—typically into a J or hockey-stick shape to allow the tip of the ET to be directed through a poorly visualized or unseen glottis.¹¹⁵ The stylet must not project beyond the end of the ET, to avoid potential laceration or perforation of the airway.

The gum elastic bougie is a blunt-ended, malleable rod which at direct laryngoscopy may be passed through the poorly or nonvisualized larynx by putting a J-shaped bend at the tip and passing it blind in the midline upward beyond the base of the epiglottis. Then, keeping the laryngoscope in the same position in the pharynx, the ET can be “railroaded” over the bougie, which is then withdrawn. For many critical care practitioners, it is the first-choice adjunct in the difficult intubation situation.111,116

Different Laryngoscope or Blade

Greater than 50 types of curved and straight laryngoscope blades are available, the most commonly used being the curved Macintosh blade.²⁰ Using specific blades in certain circumstances has been both encouraged^117–119 and discouraged.¹²⁰ In patients with a large lower jaw or “deep pharynx,” the view at laryngoscopy is often improved significantly, by using a size 4 Macintosh blade (rather than the more common adult size 3). This ensures the tip of the blade can reach the base of the vallecula to lift the epiglottis. Other blades, such as the McCoy, may be advantageous in specific situations.^121,122

Lighted Stylet

A lighted stylet (light wand) is a malleable fiberoptic light source that can be passed along the lumen of an ET to facilitate blind intubation by transillumination. It allows the tracheal lumen to be distinguished from the (more posterior) esophagus on the basis of the greater intensity of light visible through anterior soft tissues of the neck as the ET passes beyond the vocal cords.¹²³ In elective anesthesia, the intubation time and failure rate with light wand–assisted intubation were similar to those with direct laryngoscopy,¹²⁴ and in a large North American survey, the light wand was the preferred alternative airway device in the difficult intubation scenario.¹²⁵ A potential disadvantage is the need for low ambient light, which may not be desirable (or easily achieved) in a critical care setting.

Video Laryngoscopy

Video laryngoscopes are intubation devices that combine modified laryngoscope blades and video technology to provide the operator with an indirect view of the glottis. Examples of video laryngoscopes include the Storz, Glidescope, McGrath, and Pentax airway scope. They are potentially useful teaching tools as they provide the operator and student with identical views.

Depending upon the manufacturer, the devices vary in design; the blades can be standard Macintosh or angulated. Video laryngoscopes with a standard Macintosh blade such as the Storz device are inserted into the oral cavity using the standard direct laryngoscope technique. After insertion, an image of the airway appears on screen. In comparison, insertion of a video laryngoscope with an angulated blade such as the Glidescope, requires insertion into the middle of the oral cavity without a tongue sweep. Once the blade tip is at the base of the tongue the device is rotated so the tip of the blade is directed at the epiglottis. A precurved stylette endotracheal tube is pushed through the glottis. The stylet is withdrawn as the ET reaches the vocal cords and the ET is advanced downward.¹²⁶ The Pentax airway scope has a video display incorporated into the handle. The transparent blade has two channels, one for the ET and the second to facilitate suctioning.¹²⁷ The McGrath laryngoscope also had a camera mounted on a blade allowing the operator to focus on the patients face and the screen simultaneously.¹²⁸

In contrast, optical laryngoscopes do not have a video attachment but instead uses a lens to provide a view of the glottis not obtained with direct laryngoscopy. The Airtraq optical laryngoscope has a blade with an optical channel and a guiding channel for the ET. It permits glottic visualization in a neutral head position.¹²⁹

Multiple controlled and observational studies suggest that video laryngoscopy can provide superior views of the glottis compared to direct laryngoscopy.130,131 They may be particularly useful in patients with cervical instability, either by providing a better glottic view or by a reduction in upper cervical movement during intubation.^132,133 However, an improved laryngeal view does not always equate to a successful intubation. Intubation time can also be prolonged with the video laryngoscope, especially in inexperienced hands.¹³⁴ The role of the video laryngoscope in the known or anticipated difficult airway is unclear. A recent meta-analysis concluded that data on these devices in the patient with a difficult airway are inadequate.¹³¹ Current data do not suggest these devices should supersede standard direct laryngoscopy for routine or difficult airways. Further research in this area is needed.

Fiberoptic Intubation

The fiberoptic bronchoscope can be used in the unanticipated difficult airway if it is readily available and the operator is skilled.58,135,136 With an anesthetized patient, the technique may be more difficult. Loss of muscle tone will tend to allow the epiglottis and tongue to fall back against the pharyngeal wall. This can be counteracted by lifting the mandible.

Cannot Intubate–Cannot Ventilate

“Cannot intubate–cannot ventilate” is an uncommon but life-threatening situation best managed by adherence to an appropriate algorithm.52,53,104 All personnel involved will be pressured (and motivated) by the potential for severe injury to the patient. Efficient teamwork will be more likely in an environment that is relatively calm. Although it may be difficult, shouting, impatience, anger, and panic should be avoided in such situations. Figure 2.5 presents a simple flow sheet summarizing the appropriate actions.¹³⁷

Figure 2.5 Flow chart for the “cannot intubate–cannot ventilate” scenario.

Confirming Tube Position in the Trachea

A critical factor in the difficult airway scenario, potentially leading to death or brain injury, is failure to recognize misplacement of the ET. Attempted intubation of the trachea may result in esophageal intubation. This alone is not life-threatening unless it goes unrecognized.¹³⁸ Thus, confirmation of ET placement in the trachea is essential.

Visualizing the ET as it passes between the vocal cords into the trachea is the definitive means of assessing correct tube positioning. This may not always be possible, however, owing to poor visualization. In addition, the laryngoscopist may be reluctant to accept that the ET is not in the trachea. Several clinical observations support the presence of the ET in the trachea.

Chest wall movement with positive-pressure ventilation (manual or mechanical) is usual but may be absent in patients with chronic obstructive pulmonary disease (COPD), obesity, or decreased compliance (e.g., in severe bronchospasm). Although condensation of water vapor in the ET suggests that the expired gas is from the lungs, this also may occur with esophageal intubation. The absence of water vapor usually is indicative of esophageal intubation. Auscultation of breath sounds (in both axillae) supports correct tube positioning but is not absolute confirmation.¹³⁹ Apparent inequality of breath sounds heard in the axillae may suggest intubation of a bronchus by an ET that has passed beyond the carina. Of note, after emergency intubation and clinical confirmation of the ET in the trachea, 15% of ETs may still be inappropriately close to the carina.¹⁴⁰

The use of capnography to detect end-tidal carbon dioxide is the most reliable objective method of confirming tube position and is increasingly available in critical care.¹⁴¹ False-positive results may be obtained initially when exhaled gases enter the esophagus during mask ventilation¹⁴² or when the patient is generating carbon dioxide in the gastrointestinal tract (as with recent ingestion of carbonated beverages or bicarbonate-based antacids).¹⁴³ A false-negative result (ET in trachea but no carbon dioxide gas detected) may be obtained when pulmonary blood flow is minimal, as in cardiac arrest.¹⁴⁴ Visualizing the trachea or carina through a fiberoptic bronchoscope, which may be readily available in critical care, also will confirm correct placement of the ET.

Surgical Airway

The indication for a surgical airway is inability to intubate the trachea in a patient who requires it, and the techniques available are cricothyrotomy and tracheostomy.

Cricothyrotomy

Cricothryotomy may be performed as a percutaneous (needle) or open surgical procedure (Box 2.8). The indication for both these techniques is the “cannot intubate–cannot ventilate” situation. Although needle cricothyrotomy is an emergency airway procedure, the technique is similar to that for “mini-tracheostomy,” which is performed electively. Unlike the other surgical airway techniques, a needle cricothyrotomy does not create a definitive airway. It will not allow excretion of carbon dioxide but will produce satisfactory oxygenation for 30 to 40 minutes. It can be viewed as a form of apneic ventilation (see later discussion). There are several methods of connecting the intravenous cannula to a gas delivery circuit with the facility to ventilate, using equipment and connections readily available in the hospital. The appropriate method thus should be thought out in advance and available on the difficult airway trolley or bag. New commercial kits that come preassembled also are available.

Box 2.8 Procedure

Needle and Surgical Cricothyrotomy

The cricothyroid membrane is diamond-shaped and lies between the thyroid and the cricoid cartilages. Inject subdermal lidocaine and epinephrine (adrenaline) for local anesthesia.

A surgical cricothyrotomy allows a cuffed tube to be inserted through the cricothyroid membrane into the lower larynx or upper trachea. This allows positive-pressure ventilation for considerable periods and also protects against pulmonary aspiration.

Tracheostomy

A tracheostomy is an opening in the trachea—usually between the second and third tracheal rings or one space higher—that may be created surgically or made percutaneously.145–149 The indications for and contraindications to tracheostomy are summarized in Box 2.9. In comparison with long-term orotracheal or nasotracheal intubation, tracheostomy often contributes to a patient who is less agitated, requires less sedation, and who may wean from ventilation more easily.^51,150 This increased ability to wean is sometimes attributed to reduced anatomic dead space. The potential reduction in sedation after tracheostomy, however, is a much greater advantage to weaning than the small reduction in dead space. The benefits and complications of tracheostomy are listed in Box 2.10. Percutaneous tracheostomy is becoming increasingly common and typically is carried out by medical staff in the ICU (Box 2.11).

Another technique involving retrograde (inside-out) intubation of the trachea has been developed: A specially designed tracheal tube is used to keep the neck tissues under tension until tube placement has been accomplished.¹⁴⁷ It is a more time-consuming technique that at present is not widely practiced.

Although no consensus exists on what defines prolonged tracheal intubation, or when tracheostomy should be performed,¹⁵¹ most ICUs convert the intubated airway to a tracheostomy after 1 to 3 weeks, with earlier tracheostomy becoming increasingly favored.^150,151

Conventional wisdom states that the tracheostomy procedure is more complex and time-consuming than a surgical cricothyrotomy and should be performed only by a surgeon.¹⁵² Studies in the elective ICU situation suggest that cricothyrotomy is simpler and (at worst) has a similar complication rate.^153,154 Although needle cricothyrotomy has long been advocated as a life-saving emergency intervention,¹⁵⁵ recent work suggests that surgical cricothyrotomy is the more advantageous procedure.¹⁵⁶ In patients with unfavorable anatomy, surgical cricothyrotomy is a viable alternative to elective tracheostomy.¹⁵³ Surgical cricothyrotomy has been viewed as a temporary airway that should be converted to tracheostomy within a few days, but it may be used successfully as a definitive (medium-term) airway,^157,158 thereby avoiding conversion from cricothyrotomy to tracheostomy, which can cause significant morbidity.^159,160

Extubation in the Difficult Airway Patient (Decannulation)

The patient with a difficult airway still poses a problem at extubation, because reintubation (if required) may be even more difficult than the original procedure. Between 4% and 12% of surgical ICU patients require reintubation ¹⁶¹ and may be hypoxic, distressed, and uncooperative at the time of reintubation. The presence of multiple risk factors for difficult intubation,¹⁰⁰ as well as acute factors such as airway edema and pharyngeal blood and secretions, makes reestablishing the airway in such patients challenging. Before extubation of any critical care patient, the critical care team should have formulated a strategy that includes a plan for reintubation.

Stylets (airway exchange catheters) that allow gas exchange either by jet ventilation or by insufflation of oxygen may be useful in extubating the difficult airway patient.53,162,163 The stylet is placed through the ET, with care taken to ensure that the distal end has not reached as far as the carina. The ET can then be removed after a successful leak test. The stylet may remain in situ until the situation is judged to be stable.¹⁰⁰

Tube Displacement in the Critical Care Unit

Endotracheal Tube

ET displacement in the ICU is a life-threatening emergency that may result in significant morbidity.¹⁶⁴ Although tube dislodgement sometimes is viewed as unavoidable, often preventable factors are involved.^165–167 Changes in patient posture or head position cause significant movement of the tube within the trachea.^168,169 The frequency of tube displacement can be reduced by good medical and nursing practice,¹⁷⁰ attention to the arrangements and ergonomics around the bed, achieving appropriate sedation levels, and ensuring adequate ICU nurse staffing.^171,172 Experience and the ability to anticipate possible glitches constitute an important part of prevention. The management of ET displacement starts with an assessment of whether the patient can manage without the ET.¹⁶⁷ If replacement is required, preparations for a potentially difficult reintubation are indicated.

Tracheostomy Tube

Adverse events with tracheostomy tubes are quite common.167,173 Displacement may be a life-threatening event,¹⁷⁴ especially if the tube has been in place less than 5 to 7 days¹⁵¹ (before a well-defined tract between skin and trachea is formed) or if the procedure has been performed percutaneously (so that the external opening of the tract may not easily admit a new tube of the same size). The option to leave the patient without a tube should be considered, and if this option is pursued, the tracheostomy opening should be dressed to make it (to some degree) “airtight”—thus facilitating effective coughing. If the patient needs a tube but replacing the tracheostomy is not possible, then oral reintubation should be performed, after which the tracheostomy should be dressed. With a more mature tracheostomy (more than 7 days old), it usually is possible to insert a new tube through the mature tract between skin and trachea.¹⁵¹

Tracheostomy tubes may be displaced from the lumen of the trachea but appear to be normal when viewed externally. Difficulty with breathing, ventilation, or tracheal suctioning or the presence of a pneumothorax, pneumomediastinum, or surgical emphysema may be due to tracheostomy tube displacement. Fiberoptic assessment of the tube position and patency may be very useful. Assessing tracheostomy tube position on the chest x-ray film is of no value.

The NAP4 Project

The Royal College of Anaesthetists (UK) national audit project (NAP4) provided significant insight into contemporary airway management.¹⁷⁵ The project, using a 2-week national sample, estimated that approximately 2.9 million general anesthetics are administered in the United Kingdom’s National Health Service (NHS) each year. Airway management involved a supraglottic airway device (SAD) in 56% of cases, a tracheal tube in 38%, and a facemask in 5%.

The study looked at airway complications during anesthesia and also in airway management in emergency departments and ICUs across the NHS hospital system. There were 16 deaths associated with the 2.9 million anesthetics and an additional 108 patients who suffered severe or moderate harm. Airway management in the ICU and emergency department was judged to be responsible for 22 deaths with an additional 28 patients suffering severe or moderate harm.

Failure to plan (ahead) appeared to be a common causative factor in a large number of poor airway outcomes. This was sometimes due to (1) poor assessment (no recognition that there was a potential problem needing a plan), (2) failure to plan even when potential problems were recognized, and (3) failure to have alternative plan(s) (in the event that “Plan A” was not successful). Many poor outcomes are the result of repeated use of an approach that has already (sometimes repeatedly) failed.176,177

NAP4 revealed a number of scenarios or patient-related factors that seemed to predispose to poor airway outcomes. These predictors are summarized in Box 2.12.

Box 2.12

Predictors for Poor Airway Outcomes

Use of a supraglottic airway (only) in patients with a recognized airway difficulty

Cases in which awake fiberoptic intubation was indicated, but not used

Failure to use capnography or failure to interpret capnography trace correctly

Airway maneuvers in obese patients, in the emergency department or the intensive care unit

Use of emergency cannula cricothyrotomy (60% failure rate)

Displacement of a tracheostomy tube

From Cook TM, Woodall N, Frerk C (eds): The NAP4 report: Major complications of airway management in the UK: Results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Br J Anaesth 2011;106:617-631. Available at http://www.rcoa.ac.uk/index.asp?PageID=1089. Accessed 30 March 2011.

Common Problems in Airway Management

Problem 2.1 Ineffective (Spontaneous) Breathing Despite Artificial Airway

Underlying Causes

1. Obstructed airway

2. Depressed respiratory drive (influence of drugs)

3. Inefficient respiratory effort (e.g., from fractured ribs or diaphragmatic injury)

4. Pulmonary pathologic process (pneumonitis, contusion, collapse, consolidation)

Action

Attempt to deliver 100% oxygen. Check airway. When airway obstruction has been corrected or ruled out, the patient’s respiratory status should improve unless another underlying pathologic process is present. If no improvement is obtained, manually ventilate the patient. If respiratory status still fails to improve, proceed to tracheal intubation with manual or mechanical ventilation. Investigate and treat any underlying condition.

Problem 2.2 Ineffective Manual Ventilation Despite Artificial Airway

Potential Causes

1. Obstructed airway

2. Poor seal or poor technique with mask or manual ventilation

3. Pulmonary pathologic process (pneumonitis, contusion, collapse, consolidation)

Action

Attempt to deliver 100% oxygen at 15 to 20 L per minute. Check and readjust airway and patient head position. When airway obstruction has been corrected or ruled out, use a two-handed approach for mask and airway, with an assistant squeezing the bag. If no improvement is obtained, check for availability of someone with more airway experience. If no such person is available, proceed to tracheal intubation with manual or mechanical ventilation. Investigate and treat any underlying condition.

Problem 2.3 Unilateral Chest Movements in the Intubated Ventilated Patient

Potential Causes

1. Bronchial intubation

2. Bronchial obstruction

3. Lung collapse, pneumothorax

4. Hemothorax, pleural effusion

5. Consolidation, absent lung (pneumonectomy)

Action

If bronchial intubation is suspected, deflate the tracheal tube cuff and slowly withdraw the tube 1 to 2 cm. Reinflate the cuff, and manually ventilate the patient while auscultating both sides of the chest. Is air entry present and equal on both sides? Be suspicious if the tube has to be withdrawn more than 3 to 4 cm or if the tube length at the teeth is much less than the expected correct length; another underlying cause may be involved. In an adult, the average distance from the vocal cords to the carina is 12 cm. The tip of an 8.0 (adult) tracheal tube typically is 6.5 cm below the upper surface of the balloon, which must sit below the vocal cords. Therefore, if the upper surface of a cuff is only 3 cm below the vocal cords, the tip will be within 2 to 3 cm of the carina. It is easy to inadvertently intubate a bronchus or leave the tip of the tube close enough to enter the bronchus with head movement or when moving the patient. In adults with normal bronchial anatomy, the tube tip usually will pass into the right main bronchus.

Problem 2.4 Sudden Airway or Ventilatory Compromise in Ventilated Patient with Orotracheal Tube

A ventilated patient with an orotracheal tube in place may suddenly develop dyspnea, hypoxemia, hypercarbia, and a seesaw respiratory pattern. The mechanical ventilator alarm will sound.

Potential Causes

1. Failure of oxygen or air supply to the ventilator

2. Ventilator disconnection or obstruction in ventilator circuit

3. Obstructed tracheal tube

• Plugged by mucus or clot

• Kink in tracheal tube

• Biting on tube (previous biting may have narrowed the tube)

• Obstruction of tube tip by side wall of lower airways or carina

4. Patient’s fighting against ventilator

5. Respiratory fatigue (e.g., with weaning from mechanical support or new infection)

6. Pneumothorax or tension pneumothorax

7. Rapid development of large hemothorax or pleural effusion

Action

Disconnect the patient from the ventilator, and ventilate through the tracheal tube manually. Have the ventilator and circuit checked by another appropriate staff member. High resistance or inability to inflate the lungs suggests tube obstruction or an intrathoracic problem. The (recent) inability to pass a suction catheter down the lumen is suggestive of tube obstruction. If the patient’s condition is stable or improving, a small fiberoptic bronchoscope or laryngoscope (if readily available) may be passed down the tube. An obstruction may be removed by suction catheter, or removal of the tube and use of mask ventilation (to reverse hypoxemia and hypercarbia), followed by reintubation, may be required. If no answer to the problem is found, consider whether the patient’s condition could be due to a tension pneumothorax. If appropriate, use needle decompression. Otherwise, order emergency chest film and continue either manual or mechanical ventilation as appropriate.

Problem 2.5 Sudden Airway or Ventilatory Compromise in Ventilated Patient with Tracheostomy

A ventilated patient with a tracheostomy may suddenly develop dyspnea, hypoxemia, hypercarbia, and a seesaw respiratory pattern. The mechanical ventilator alarm will sound.

Potential Causes

Causes may include all those listed for Problem 2.4.

Action

Appropriate interventions are the same as for Problem 2.4, with an appreciation of the fact that tracheostomy tubes are shorter, more curved, and more rigid than tracheal tubes. They rarely kink but may become blocked with secretions or blood.^31,178 Suctioning the tube may resolve this. Double-skinned tracheostomy tubes may be unblocked by removing the inner tube (containing the obstruction) for washing, leaving the outer tube in place to maintain a clear airway. Such double-skinned tubes are safer for patients discharged to general wards. Tracheostomy tubes also may become obstructed when the distal opening is blocked by a mucosal flap, the side wall of the trachea, or (rarely) the carina.

Key Points

• The difficult airway may be unanticipated despite expert preassessment. Airway practitioners must have plans to deal with this scenario.

• Use of the appropriate size and type of laryngoscope blade in conjunction with other adjuncts and techniques is an important element of successful tracheal intubation—particularly with the unanticipated difficult airway.

• Airway difficulty in critical care is common and may be precipitated long after intubation by acute events such as tube dislodgement or obstruction.

• Tube dislodgement in critical care is potentially avoidable and may be influenced by staffing levels, sedation policy, and other bedside factors.

• Surgical cricothyrotomy is a relatively simple procedure and may be used to establish a medium-term airway, avoiding the need for tracheostomy.

• In critical care, removal of a tracheal tube may precipitate an acute difficult airway scenario. A protocol for handling a difficult reintubation should always be in place.

• All critical care physicians should be familiar with one or more difficult airway algorithms and the practical skills they require.