Airway Intubation
KEY POINTS
1 Noninvasive ventilation may not be appropriate for patients who cannot protect the airway, for those who are obtunded or uncooperative, for those in whom unexpected loss of pressure or enriched oxygen might be immediately hazardous, for those who require high levels of applied pressure, or for those who are hemodynamically unstable. In such cases, endotracheal intubation is the indicated intervention.
2 Orotracheal tube placement is the method of choice during emergencies and most critical care applications. Another option in more elective situations is the nasotracheal route, which requires tubes of generally smaller diameter than tubes used for orotracheal intubation. Although nasotracheal intubation is more comfortable and stable in the conscious or active patient, it is associated with sinusitis, presents higher airway resistance, impedes secretion extraction, and is not recommended for long-term use.
3 Important complications of intubation include a variety of insertion trauma, gastric aspiration, hypoxemia, laryngospasm, esophageal intubation, right main bronchus intubation, cardiac arrhythmias, and hemodynamic impairment.
4 Predictors of difficult intubation include nonvisibility of key oropharyngeal landmarks, poor atlanto-occipital joint mobility, short mentohyoid distance, mentothyroid distance less than 6 cm, mentosternal distance less than 12 cm, and restricted temporomandibular joint excursion. In such cases, the need for special expertise and specialized tools for airway management should be considered before the attempt.
5 Instruments and techniques facilitating the intubation process include fibrobronchoscopy, lighted stylet guidance, specialized laryngoscopes, directed-tip endotracheal tubes, and retrograde wire insertion. Traditional methods to confirm tracheal positioning of the endotracheal tube include stethoscopically audible symmetry of breath sounds, ease of manual insufflation, complete recovery of insufflated tidal volume, loss of voice, expansion of the upper chest, squeeze bulb or syringe recovery of small injected gas volumes, and coughing with expulsion of airway secretions. Currently, CO2-sensing indicators play an important role for this purpose.
6 Inadvertent extubation is often a life-threatening event that occurs more commonly in orally intubated, lightly sedated patients (who must be carefully restrained). The ability of positive end-expiratory pressure to blow gas freely around a deflated cuff gives some assurance of patency of the larynx above the cuff immediately before a planned extubation.
7 Although its long-term complications can be serious, tracheostomy improves comfort, communication, secretion management, and allows intermittent disconnection of the ventilator. Certain newer variants of conventional tracheostomy (e.g., needle cricothyroidotomy, percutaneous dilatational tracheostomy, and minitracheostomy) do not require an operating room and often prove more convenient or safer to perform in well-selected acutely ill patients.
▪ INDICATIONS
Primary indications for endotracheal (ET) intuba tion include (a) the need for assisted ventilation or the delivery of high levels of inspired oxygen, (b) airway protection against aspiration, (c) clearance of secretions retained in central airways, and (d) relief of upper airway obstruction (Table 6-1).
TABLE 6-1 INDICATIONS FOR ORAL INTUBATION, NASAL INTUBATION, AND TRACHEOSTOMY ORAL NASAL TRACHEOSTOMY | ||||||
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Need for Assisted Ventilation and Positive End-Expiratory Pressure
Intubation of the trachea with a cuffed tube remains the only viable option for simultaneously securing the airway, allowing repeated access to the trachea and providing effective ventilatory support. Recent advances in noninvasive ventilation, however, mandate that the indications for airway intubation must be defined explicitly (see Chapter 7). Tracheal intubation is required when high levels of airway pressure must be applied to ensure satisfactory oxygen exchange or ventilation. Moreover, noninvasive ventilation may not be appropriate or safe for patients who are obtunded or uncooperative, for those in whom even momentary loss of ventilatory pressure or inspired oxygen might be hazardous, for those requiring high levels of applied pressure, and for those who are hemodynamically unstable. When ventilatory support must be continuous and/or extended more than a few days, intubation clearly is a better approach.
Airway Protection
Because protection of the upper airway cannot be ensured without establishing an effective seal, intubation is required for lethargic or comatose patients at high risk for aspiration. Although an inflated cuff prevents massive airway flooding, small quantities of pharyngeal contents are aspirated routinely. Seepage of the infected secretions that pool just above the cuff may help account for the high incidence of pulmonary infections that occur in mechanically ventilated patients. Special tubes that allow continued evacuation of this secretion pool have been reported to reduce the incidence of ventilatorassociated pneumonia (see Chapters 8 and 26).
Secretion Clearance
Retained airway secretions predispose to infection, encourage atelectasis, promote hypoxemia, and dramatically increase the breathing workload for patients with neuromuscular weakness and/or underlying airflow obstruction. Translaryngeal intubation and tracheostomy facilitate extraction of these secretions.
Upper Airway Obstruction
Intubation addresses the immediate threat of anatomic or functional obstruction of the upper airway and is often the first step taken before attempting definitive treatment (see Chapter 25).
▪ TYPES OF AIRWAYS AND ROUTES OF INTUBATION
Supraglottic Airways
Pharyngeal airways are firm supports placed through the nose or mouth that are intended to bypass the relaxed tongue, thereby splinting open the retropharynx and providing protected access to the hypopharynx (Table 6-2).
TABLE 6-2 INDICATIONS FOR SUPRAGLOTTIC AIRWAYS | ||||||||||
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Oropharyngeal Airways
Oral airways are anatomically contoured plastic devices that displace the tongue from the posterior wall of the pharynx to prevent occlusion. Their primary purpose is to wedge open the hypopharynx and to facilitate secretion extraction during spontaneous breathing or bag-mask ventilation. Well-placed oropharyngeal airways allow unimpeded spontaneous or assisted ventilation and facilitate removal of airway or pharyngeal secretions. Temporary placement of an oropharyngeal airway allows effective delivery of topical anesthetic to the larynx prior to placement of an ET tube. It is not intended to substitute for ET intubation in patients with firm indications for airway protection or who require secure access to the lower airway.
An oral airway can either serve as a “bite block” for an orally intubated patient inclined to jaw clenching. Because they stimulate the retropharynx and promote gagging, oral airways must not be used in alert patients or in those with intact gag reflexes. (Over time, however, some accommodation to this foreign object may develop.) Disturbingly, obtunded patients with depressed gag reflexes are just those who are most inclined to aspirate. These oropharyngeal airways must, therefore, be removed as soon as consciousness returns or evidence for an activated gag reflex appears.
Nasopharyngeal Airways
These firm (but compressible), curved, flanged, and hollow tubes (nasal “trumpets”) are available in a variety of diameters and lengths, but none are designed to extend into the glottis. They are inserted through a lubricated, topically anesthetized, and widely patent nasal passage to facilitate extraction of secretions from the hypopharynx or to guide the passage of tracheal suction catheters. For many patients, they are especially useful in the period immediately after extubation, when swallowing of oropharyngeal secretions and effective coughing are impaired. Because they induce considerably less pharyngeal stimulation than do oral airways, they can be used for conscious patients and may serve temporarily as an effective conduit for topical anesthetic delivery to the retropharynx and larynx prior to intubation. Nasopharyngeal airways are best transferred to the alternate nasal passage on a daily basis. Continuous use beyond 48 to 72 h is generally inadvisable because of the escalating risk of infective and erosive complications. Although occasionally helpful in keeping the retropharynx open, they do not reliably maintain airway patency and are not an acceptable alternative to ET intubation for high-risk patients.
Laryngeal Mask Airway, King Airway, and Combitube
The laryngeal mask airway (LMA) is a device that is intended to be inserted into the pharynx without direct visualization and yet to allow effective ventilation and isolation of the lungs from the esophagus. Levels of positive pressure ≥ 20 cm H2O can be effectively applied. The insertion technique is rather easily mastered and can be implemented without deep anesthesia. Initially, the LMA was intended for out-of-hospital resuscitation, but currently it is used in surgical procedures, noninvasive and invasive radiologic procedures with short or intermediate duration (<2 h). Increasingly, it is an immediate stop-gap measure when ET intubation cannot be immediately established. LMA does not offer protection from aspiration, but new designs (like the Pro-Seal device) can facilitate gastric suctioning and decrease the risk of aspiration. In the intensive care unit (ICU) environment, the LMA may have applications as well; for example, it allows for insertion of a bronchoscope-guided ET tube via an on-board channel while supporting ventilation. An LMA can therefore serve as a useful backup option for intubating—or reintubating—the difficult airway (LMA is included in the American Society of Anesthesia’s Difficult Airway Management Algorithm.). For emergent placement of a reliable airway, the King airway may represent the easiest and most reliable
option. The Combitube, a cuffed, bilumen, perforated tube, performs as a combined esophageal obturator and tracheal conduit. It is usually inserted blindly and affords both ventilation of the lungs and some protection from aspiration, whether or not the lumen ideally intended for the trachea actually rests there. (It usually does not.)
option. The Combitube, a cuffed, bilumen, perforated tube, performs as a combined esophageal obturator and tracheal conduit. It is usually inserted blindly and affords both ventilation of the lungs and some protection from aspiration, whether or not the lumen ideally intended for the trachea actually rests there. (It usually does not.)
Endotracheal Intubation
Orotracheal Tubes
As a rule, orotracheal (OT) tubes are easier to insert than nasotracheal (NT) tubes, making oral placement the method of choice during emergencies. The larger tube passed by the oral route improves both airway resistance and secretion management and allows passage of a standard caliber fiberoptic bronchoscope (FOB) should the need arise. Variations of OT tubes are available that allow selective main bronchial intubation, allow aspiration of supraglottic secretions (above the cuff), allow direct fiberoptically imaged visualization of the trachea and main carina, provide an intramural lumen for dead space washout by fresh gas injected near the tube tip, and offer a variety of other unusual and occasionally useful functions. However, oral tubes are not without disadvantages, as they are less stable and less comfortable than nasal tubes, and they impair swallowing to a greater extent. Most self-extubations occur in patients who are orally intubated. They often require an additional oral appliance for stabilization and to prevent tube occlusion by biting. During insertion, OT tube placement incurs a higher incidence of retching, vomiting, aspiration, and mainstem bronchus intubation than the nasal approach, and oral tubes seriously compromise oropharyngeal hygiene. Finally, conventional OT intubation should only be attempted very carefully in patients with limited neck mobility (e.g., ankylosing spondylitis, rheumatoid arthritis, cervical spinal trauma, or prior surgery). Devices are now available to facilitate OT intubation and airway management in such difficult cases. These include fiberoptic intubating bronchoscopes, illuminated stylets, and gum elastic bougies (see following).
Nasotracheal Tubes
NT tubes present a comparatively high resistance to airflow because they are relatively long, kink easily, and impose unusually high resistance when lined with thickened secretions. Even when of normal caliber, the nares do not admit tubes as large as those that the oropharynx will accept. NT tubes are often difficult and sometimes painful to insert. Traumatic complications of NT tube insertion include damage to turbinates, polyps, and wellvascularized mucosa. Insertions should never be forced and should not be attempted in patients who do not easily admit a lubricated nasal trumpet on the same side. Severe hemorrhage can result from ill-advised nasal intubation attempts in patients with bleeding predispositions. Coagulopathy, narrow or deformed nasal passages, and nasal polyposis are contraindications. In a significant percentage of patients, purulent nasal discharge or sinusitis may develop after 72 h. Once in place, however, nasal tubes allow better communication, swallowing, mouth hygiene, and anchoring than their oral counterparts. Nasal tubes offer clear advantages for patients with cervical spine disease and for those with a variety of oral, mandibular, and temporomandibular problems. The relative indications for placing OT tubes, NT tubes, and tracheostomies are summarized in Table 6-2.
▪ PHYSIOLOGIC RESPONSES TO INTUBATION
During the intubation of a lightly anesthetized normal adult, increases of heart rate and blood pressure are mediated by neural reflexes, catecholamines, and stress hormones. Moreover, bradycardia, cardiac arrhythmias, and arterial hypotension can be provoked. These cardiovascular effects are blunted by sedatives, analgesics, and systemic or topical anesthetics. Conversely, intravenous anesthetics frequently elicit hypotension, especially in patients with hypovolemia. In current ICU practice, a frequent offender is propofol, which should be given at less than customary rates in the elderly, debilitated, and critically ill. Thiopental’s myocardial depressive and vasodilating actions are dose dependent and occur routinely in hypovolemic subjects. Ketamine, a drug used commonly for intubations in the operating theater, preserves laryngeal and pharyngeal reflexes, but is not recommended in patients with raised intracranial pressure, except if the patient is hypovolemic and hypotensive. Etomidate is frequently used and is generally safe and effective; however, this drug may interfere with adrenocortical output for days after the dose is given. Laryngoscopy can impressively raise intracranial pressure, and special precautions to minimize this effect are indicated for patients
with head trauma or other at-risk condition. Clinically significant laryngospasm and bronchospasm occur infrequently in a well-prepared subject.
with head trauma or other at-risk condition. Clinically significant laryngospasm and bronchospasm occur infrequently in a well-prepared subject.
By definition, an ET tube cannot exceed the caliber of the larynx, which normally is the site of greatest narrowing within the native airway. Consequently, intubation reduces the dead space of the upper airway by 20 to 60 mL but simultaneously increases the resistance to airflow. Moreover, once inserted, the resistance offered by a bent, kinked, and secretion-lined or clot-obstructed ET tube in situ can be considerably greater than its manufacturing specification. Although certain reports suggest that intubation reduces the resting lung volume and alters the breathing pattern, the available evidence is conflicting and there is no firm consensus on these points.
▪ COMPLICATIONS OF AIRWAY INTUBATION
Anatomic Impairment
ET tubes bypass the mechanical defenses of the upper airway, contaminate the lower airways, and severely hamper effective coughing. Despite advances in materials and cuff design, all tubes have the potential of inflicting laryngeal and tracheal injury during insertion and none completely protect the lungs against aspiration of liquids. Furthermore, the supraglottic pool of oral secretions that seep past the cuff as well as the biofilm that routinely lines the lumen of the tube serve to repeatedly inoculate the lower airway with potential pathogens.
Insertion Trauma
Inexpert placement of an ET tube may injure delicate labial, laryngeal, nasal, and pharyngeal tissues or cause dental or spinal trauma. Epistaxis occurs in a sizable percentage of patients who are intubated nasotracheally. Mouth trauma, tooth dislodgement, and mandibular dislocation can result from forceful use of the laryngoscope and placement of an OT tube. Most laryngeal injuries that result from intubation with normally inflated tubes having soft, high-volume cuffs are mild and easily healed. The formation of granulation tissue and ulcers by pressure-induced mucosal ischemia, however, can cause major trouble. Such complications may be observed when tight-fitting (oversized) ET tubes and unrelieved excessive cuff pressure are used for long durations. Carinal injury has been reported as consequence of traumatic insertion of an ET tube. Bilateral vocal cord paralysis and arytenoid cartilage dislocation typically present as postextubation hoarseness and upper airway obstruction. Use of a nasogastric tube in conjunction with oral intubation has been associated with a higher incidence of aspiration, mucosal erythema, and granuloma formation. Rarely, a tracheoesophageal fistula may form generally after prolonged intubation.
Hypoxemia
Patients who require supplemental O2 often are exposed to room air during intubation, with consequent desaturation of arterial blood. Although this risk is reduced by “preoxygenation,” O2 stored in this way is depleted quickly by deep breathing, especially in patients with seriously impaired gas exchanging function. Therefore, intubation attempts should not be prolonged beyond 30 s before “reoxygenating,” especially for patients who continue to breathe actively. Pulse oximetry provides a useful but delayed signal that helps warn of developing hypoxemia during the attempt. Nasal prongs set to deliver 6 to 10 L of oxygen per min can provide supplemental O2 during oral intubation, as can the use of a laryngoscope adapted for this purpose.
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