Ron M. Walls
Introduction
Loss of the airway, with resultant failure of ventilation and oxygenation, is the terminal pathway for many patients. Timely, effective, and decisive airway management in an emergency can mean the difference between life and death or between ability and disability. In the emergency department (ED), responsibility for airway management resides with the emergency physician. As such, airway management is the single most important skill of the emergency physician, and emergency airway management is one of the defining domains of the specialty of emergency medicine.
The emergency physician is responsible for airway management for patients in the emergency department.
Increasingly, nonanesthesiologists, such as hospitalists or intensivists, are the primary responders to airway emergencies arising on hospital inpatient units. Paramedics and critical care transport personnel are responsible for the out-of-hospital airway. These practitioners must maintain the cognitive base and technical skill set required for swift, decisive airway management, which is often required without warning and in a suboptimal environment.
The emergence of new technology, such as various methods of video and fiberoptic laryngoscopy, is changing the fundamental approach to airway decision making, particularly with respect to difficult intubation. Nevertheless, emergency airway management, whether in the ED or elsewhere in the hospital or prehospital setting, still comprises a definable series of complex actions, each requiring mastery:
· Rapidly assess the patient's need for intubation and the urgency of the situation.
· Determine the best method of airway management.
· Decide whether pharmacological agents are indicated, which to use, in what order, and in what doses.
· Use one of myriad airway devices proficiently to achieve a definitive airway while minimizing the likelihood of hypoxemia, hypercarbia, and aspiration.
· Recognize when the planned airway intervention has failed, and quickly and effectively choose and execute an alternative (rescue) technique.
Physicians responsible for emergency airway management must be proficient with rapid sequence intubation, which requires a thorough knowledge of the pharmacology and effects of neuromuscular blocking agents, sedative or induction agents, and other medications that are used to improve outcome or mitigate adverse effects. The entire repertoire of airway skills must be mastered, ranging from bag-mask ventilation to rapid sequence intubation, techniques for the difficult airway, and rescue maneuvers, including surgical airway techniques, in the event of airway management failure. Emergency airway management requires diligent maintenance of both knowledge and technical bases, continuous learning, sound clinical judgment, and the decisiveness to act when action is indicated. This chapter focuses on the decision to intubate. Subsequent chapters describe the technique of rapid sequence intubation and its place in the new emergency airway algorithms. The airway is rightfully allocated the “A” in the ABC (airway, breathing, circulation) of resuscitation, and in all cases, the airway is paramount and takes precedence over other clinical considerations. Without a secure airway and adequate oxygenation and ventilation, other resuscitative measures are doomed to failure. With the exception of the immediate defibrillation of the cardiac arrest patient, no single resuscitative maneuver takes priority over management of the airway.
Indications for Intubation
The decision to intubate should be based on three fundamental clinical assessments:
1. Is there a failure of airway maintenance or protection?
2. Is there a failure of ventilation or oxygenation?
3. What is the anticipated clinical course?
The results of these three evaluations will lead to a correct decision to intubate or not to intubate in virtually all conceivable cases.
A. Is there a failure of airway maintenance or protection?
A patent airway is essential for adequate oxygenation and ventilation, and protection of this airway against aspiration of gastric contents is vital. The conscious, alert patient uses the musculature of the upper airway and various protective reflexes to maintain a patent airway and to protect against the aspiration of foreign substances, gastric contents, or secretions. The ability of the patient to phonate with a clear, unobstructed voice is strong evidence of both airway patency and protection. In the severely ill or injured patient, such airway maintenance and protection mechanisms are often attenuated or lost. If the patient is not able to maintain an adequate airway, an artificial airway may be established by insertion of an oropharyngeal airway or a nasopharyngeal airway. Although such airway devices may restore a patent airway, they do not provide any protection against aspiration. As a general rule, any patient who requires the establishment of an airway also requires protection of that airway, and the use of an oropharyngeal or nasopharyngeal airway should be considered a temporizing measure, pending establishment of a definitive airway.
Any patient who requires the establishment of an airway also requires maintenance and protection of that airway.
A patient who is seemingly able to maintain a patent airway and adequate gas exchange cannot be assumed to be able to protect the airway against the aspiration of gastric contents, which carries a significantly increased risk of morbidity and mortality. It has been widely taught that the gag reflex is a reliable method of evaluating airway protective reflexes. In fact, this concept has never been subjected to adequate scientific scrutiny, and the absence of a gag reflex is neither sensitive nor specific as an indicator of loss of airway protective reflexes. The presence of a gag reflex has similarly not been demonstrated to ensure the presence of airway protection. In addition, testing the gag reflex in a supine, obtunded patient may result in vomiting and possible aspiration. Overall, the gag reflex is not recommended for assessment of airway protection or the need for intubation.
The gag reflex is of no clinical value when assessing the need for intubation.
Evaluation of the ability to swallow spontaneously and to handle normal oropharyngeal secretions is probably a better measure of the patient's ability to protect the airway. Swallowing is a complex reflex that requires the patient to sense the presence of material in the posterior oropharynx, and then to execute a series of intricate and coordinated muscular actions to direct the secretions down past a closed airway into the esophagus. Although this concept also has not been adequately studied, the assessment of spontaneous or volitional swallowing is probably a better tool for assessing the ability to protect the airway than is the presence or absence of a gag reflex. The presence of pooled secretions in the patient's oropharynx should be considered to indicate a potential failure of airway protection. In the absence of an immediately reversible condition, such as opioid overdose or reversible cardiac dysrhythmia, prompt intubation is indicated for any patient who is unable to maintain and protect the airway. A common clinical error is to assume that simply because the patient is “breathing on his or her own,” the ability to protect the airway is preserved. Although spontaneous ventilation may be adequate, the patient may be sufficiently obtunded to be at risk for serious aspiration.
B. Is there a failure of ventilation or oxygenation?
If the patient is unable to ventilate adequately, or if adequate oxygenation cannot be achieved despite the use of supplemental oxygen, then intubation is indicated. In such cases, the intubation is being performed to facilitate ventilation and oxygenation rather than to establish or protect the airway. An example is the patient with status asthmaticus, who will generally maintain and protect the airway even when in extremis. However, fatigue produces ventilatory failure and, combined with mucous plugging, the resultant hypoxemia will lead to respiratory arrest and death without intervention. Similarly, although the patient with severe adult respiratory distress syndrome may be maintaining and protecting the airway, he or she may have progressive oxygenation failure that can be managed only with endotracheal intubation and positive-pressure ventilation. Unless ventilatory or oxygenation failure is due to a reversible cause, such as opioid overdose, intubation is required.
C. What is the anticipated clinical course?
Most patients who require emergency intubation have one or more of the previously discussed indications: failure of airway maintenance, airway protection, oxygenation, or ventilation. However, there is a large and important group for whom intubation is indicated, even though none of these four fundamental failures is present at the time of evaluation. These are the patients whose conditions, and airways, are predicted to deteriorate, either because of dynamic and progressive changes related to the presenting condition or because the work of breathing will become overwhelming in the face of catastrophic illness or injury. For example, consider the patient who presents with a stab wound to the midzone of the anterior neck and a visible hematoma. At the time of presentation, the patient may have perfectly adequate airway maintenance and protection and be ventilating and oxygenating well. The hematoma, however, provides clear evidence of significant vascular injury. Ongoing bleeding may be clinically occult because the blood often tracks down the tissue planes of the neck (e.g., prevertebral space) rather than causing visible external expansion of the hematoma. Furthermore, the anatomical distortion caused by the enlarging internal hematoma may well thwart a variety of airway management techniques that would have been successful if undertaken earlier. The patient inexorably progresses from awake and alert with a patent airway to a state in which the airway becomes obstructed, often quite suddenly, and the anatomy is so distorted that airway management is difficult or impossible.
Acute, progressive anatomical airway distortion is a potential time bomb. Intubate or visualize the airway early, before deterioration occurs!
Analogous considerations apply to the polytrauma patient who presents with hypotension and multiple severe injuries, including chest trauma. Although this patient initially has adequate airway maintenance and protection, and ventilation and oxygenation may be acceptable, intubation is indicated as part of the management of the constellation of injuries (i.e., as part of the overall management of the patient). The reason for the intubation of such patients becomes clear when one examines the anticipated clinical course of this patient. The hypotension mandates aggressive fluid resuscitation and evaluation for the source of the blood loss, including likely abdominal computed tomography (CT) scan. Pelvic fractures, if unstable, require immobilization and likely embolization of bleeding vessels. Long bone fractures often require operative intervention. Chest tubes may be required to treat hemopneumothorax or in preparation for positive-pressure ventilation during surgery. Combative behavior requires management and evaluation by head CT scan. Throughout all of this, the patient's shock state causes inadequate tissue perfusion and increasing metabolic debt. This debt significantly affects the muscles of respiration, and progressive respiratory fatigue and failure often supervene. With the patient's ultimate destination certain to be the operating room or the intensive care unit, and the need for complex and potentially painful procedures and diagnostic evaluations, which may require extended periods of time outside the resuscitation suite, this patient is best served by early intubation. In addition, intubation improves tissue oxygenation during shock and helps reduce the increasing metabolic debt burden.
Sometimes, the anticipated clinical course may be such that intubation is mandated because the patient will be exposed to a period of increased risk. For example, the patient with multiple injuries who appears relatively stable might be appropriately managed without intubation while geographically located in the ED. However, if that same patient requires CT scans, angiography, or any other prolonged diagnostic procedure, it may be more appropriate to intubate the patient prior to allowing him or her to leave the ED so that an airway crisis will not ensue in the radiology suite, where recognition may be delayed and response may not be optimal. Similarly, if such a patient is to be transferred from one hospital to another, airway management may be indicated on the basis of the increased risk to the patient during that transfer. Not every trauma patient or every patient with a serious medical disorder requires intubation; however, in general, it is better to err on the side of caution by performing an intubation that might not, in retrospect, have been required, than to delay intubation, thus exposing the patient to a potentially disastrous deterioration. A potentially destructive “fear of intubation” can lead the provider to procrastinate, delaying intubation until the need is indisputable, during which time the patient has deteriorated, and the airway has become more difficult.
If the anticipated clinical course is one of deterioration or if the critically ill or injured patient will be leaving the relatively safe confines of the emergency department, intubate early before deterioration and airway compromise occur.
Approach to the Patient
When evaluating a patient for emergency airway management, the first assessment should be of the patency and adequacy of the airway. In many cases, the adequacy of the airway is confirmed by having the patient speak. Ask questions such as “What is your name?” or “Do you know where you are?” The responses provide information about both the airway and the patient's neurological status. A normal voice, the ability to inhale and exhale in the modulated manner required for speech, and the ability to comprehend the question and follow instructions are strong evidence of adequate upper airway function. Although such an evaluation should not be taken as proof that the upper airway is definitively secure, it is strongly suggestive that the airway is adequate for the time being. More important, the inability of the patient to phonate properly, or the presence of stridor or altered mental status precluding responses to the questions mandate an immediate, detailed assessment of the adequacy of the airway and ventilation. After assessing verbal response to questions, conduct a more detailed examination of the mouth and oropharynx. Examine the mouth for bleeding, swelling of the tongue or uvula, abnormalities of the oropharynx (e.g., peritonsillar abscess), or any other abnormalities that might interfere with the unimpeded passage of air through the mouth and oropharynx. Examine the mandible and central face briefly for integrity. A careful examination of the anterior neck requires both visual inspection for deformity, asymmetry, or abnormality and palpation of the anterior neck, including the larynx and trachea. During palpation, assess carefully for the presence of subcutaneous air. This is identified by a crackling feeling on compression of the cutaneous tissues of the neck, much as if a sheet of wrinkled tissue paper were lying immediately beneath the skin. When only a small amount of subcutaneous air is present, this physical finding may be subtle and transient and must be sought carefully. The presence of subcutaneous air indicates disruption of an air-filled passage, often the airway itself, especially in the setting of blunt or penetrating chest or neck trauma. Subcutaneous air in the neck can also be caused by pulmonary injury, esophageal rupture, or, rarely, gas-forming infections. Although these latter two conditions are not immediately threatening to the airway, patients may nevertheless rapidly deteriorate, requiring subsequent airway management.
After inspecting and palpating the upper airway, note the respiratory pattern of the patient. The presence of inspiratory stridor, however slight, indicates some degree of upper airway obstruction. The volume and pitch of stridor on inspiration are related to the velocity of air flow, which in turn depends on the degree to which the patient is conscious and the strength of the inspiratory muscles. Most often, stridor is audible without a stethoscope and should not be confused with “hysterical stridor” or intermittent expiratory moaning, which is often exhibited by patients in pain. Auscultation of the neck with a stethoscope can reveal subauditory stridor that is equally concerning, indicating potential airway compromise. Significant airway compromise may develop before any sign of stridor is evident, particularly in adults. When evaluating the respiratory pattern, observe the chest through several respiratory cycles. Symmetrical, concordant chest movement is the expected finding. In cases where there is significant injury, paradoxical movement of a flail segment of the chest may be observed. If spinal cord injury has impaired intercostal muscle functioning, diaphragmatic breathing may be present. In this form of breathing, there is little movement of the chest wall, and inspiration is evidenced by apparent increase in abdominal volume caused by descent of the diaphragm. Auscultate the chest to assess the adequacy of air exchange. Decreased breath sounds caused by pneumothorax, hemothorax, or other pulmonary pathology may be detected. Acute pneumothorax rarely causes any significant degree of tracheal deviation until the patient is in extremis, and tracheal deviation, when found, will likely represent a chronic process.
The assessment of ventilation and oxygenation is a clinical one. Arterial blood gas determinations provide little additional information as to whether intubation is necessary and may be misleading. The clinical impression of the patient's mentation, degree of fatigue, and severity of concomitant injuries or conditions is more important than isolated or even serial determinations of arterial oxygen or carbon dioxide (CO2) tension. Oxygen saturation is monitored continuously by pulse oximetry, and arterial blood gases are rarely indicated for the purpose of determining arterial oxygen tensions. In certain circumstances, oxygen saturation monitoring is unsuccessful because of poor peripheral perfusion, and arterial blood gases may then be required to assess oxygenation or to provide a correlation with pulse oximetry measurements. Continuous capnography (see Chapter 39) may be used to assess changes in the patient's ability to ventilate adequately, and the measurement of arterial CO2 tension contributes little additional useful information. In patients with obstructive lung disease, such as asthma or chronic obstructive pulmonary disease, intubation may be required in the face of relatively low CO2 tensions because of patient fatigue. Other times, extremely high CO2 tensions may be managed successfully without intubation if the patient is showing clinical signs of improvement (e.g., increased alertness, improving speech, less fatigue).
Arterial blood gas values are rarely helpful in the decision to intubate and may be misleading.
Finally, after assessment of the upper airway and the patient's ventilatory status, including pulse oximetry, capnography, and mentation, consider the patient's anticipated clinical course. If the patient's condition is such that intubation is inevitable and a series of interventions is required, early intubation is preferable. Similarly, if the patient has a condition that is at risk to worsen over time, especially if such worsening is likely to compromise the airway itself, early airway management is indicated. The same consideration applies to patients who require interfacility transfer by air or ground, or a prolonged procedure in an area with diminished resuscitation capability. Intubation before transfer is vastly preferable to a difficult, uncontrolled intubation in an austere environment after the condition has worsened. In all circumstances, the decision to intubate should be given precedence. If doubt exists as to whether the patient requires intubation, err on the side of intubating the patient. It is preferable to intubate the patient and ensure the integrity of the airway than to leave the patient without a secure airway and have an irreversible, preventable catastrophe occur.
Evidence
1. Is the gag reflex a useful indicator of the need to intubate. In a study of 111 patients requiring neurological observation in the ED, Moulton et al. (1) found no correlation between the Glasgow Coma Scale (GCS) and the presence or absence of a gag reflex. The gag reflex was noted to be variably present across the range of GCS from 6 to 15, independent of the patient's perceived need for intubation (1). The gag reflex is not involved in laryngeal closure or protection of the airway. Bleach (2) found an absent gag reflex in 27% of fully conscious patients who had undergone speech therapy and videofluoroscopy to assess for possible aspiration after neurological events. There was no correlation between aspiration and the presence (or absence) of the gag reflex (2). Davies et al. (3) studied 140 healthy adults, half of whom were elderly, and found that 37% lacked any gag reflex. Chan et al. (4) studied 414 patients with acute poisoning and noted absence of the gag reflex to be only 70% sensitive in identifying patients who required intubation. Contrary to those studies that find the gag reflex frequently absent in the normal population, absence of a gag reflex was 100% specific in identifying patients requiring intubation; however, the use of a GCS score of 8 or less outperformed the gag reflex, and evaluation of the gag reflex added nothing to the assessment of the GCS score alone (4).
References
1. Moulton C, Pennycook A, Makower A. Relation between the Glasgow Coma Scale and the gag reflex. BMJ 1991;303:1240–1241.
2. Bleach N. The gag reflex and aspiration: a retrospective analysis of 120 patients assessed by videofluoroscopy. Clin Otolaryngol 1993;18:303–307.
3. Davies AE, Kidd D, Stone SP, et al. Pharyngeal sensation and gag reflex in healthy subjects. Lancet 1995;345:487–488.
4. Chan B, Gaudry P, Grattan-Smith TE, et al. The use of Glasgow Coma Score in poisoning. J Emerg Med 1993;11:579–582.