The decision to intubate

INTRODUCTION — The first step in any resuscitation is the verification or establishment of a patent and protected airway. Emergency defibrillation is the sole, occasional exception to this principle. Without adequate oxygenation, all other potentially lifesaving maneuvers will fail. Most often, clinicians secure the airway of an unstable patient through placement of a cuffed endotracheal tube.

This topic review discusses how to determine the need for intubation and provides a simple decision tool that is applicable to virtually all emergency patients regardless of age or presenting condition. Discussions of other aspects of airway management are found elsewhere.

●(See "Rapid sequence intubation in adults for emergency medicine and critical care".)

●(See "Technique of emergency endotracheal intubation in children".)

●(See "Approach to the failed airway in adults for emergency medicine and critical care".)

●(See "Approach to the difficult airway in adults for emergency medicine and critical care".)

DECIDING TO INTUBATE: THREE-QUESTION ASSESSMENT — Emergency clinicians must often perform tracheal intubation under stressful conditions. Skillful execution of tracheal intubation requires a good understanding of several methods of intubation, how to identify the potentially difficult intubation, the drugs best suited for airway management in different clinical scenarios, and management of the difficult or failed airway. Deficiency in any of these areas reduces the likelihood of a good patient outcome. (See "Rapid sequence intubation in adults for emergency medicine and critical care" and "Technique of emergency endotracheal intubation in children".)

Even knowledgeable emergency clinicians, however, can contribute to patient morbidity and mortality by waiting too long to intubate. Inappropriate delays in airway management can convert a relatively controlled opportunity to secure the airway into a hectic, unplanned situation ("crash" airway), eliminating the opportunity for a well-prepared, methodical approach. As examples, clinicians should not postpone intubation until the patient with anaphylaxis develops stridor or wait for worsening of hoarseness in the patient with smoke inhalation.

The decision to intubate can be obvious and require little deliberation, as with the comatose head-injured patient who requires immediate intubation. It may also be clear when intubation can be withheld, such as the patient in mild respiratory distress from acute heart failure who is rapidly improving with nitroglycerin and noninvasive positive-pressure ventilation (NIPPV). Between such cases lies a range of airway management scenarios where the need for tracheal intubation may be unclear. When confronting such scenarios, the emergency clinician must consider a number of factors when deciding whether intubation is needed, including the patient's respiratory status, the pathologic process and likelihood of deterioration, patient age and comorbidities, the need for transfer to another facility, and available resources.

Whenever possible, and particularly with patients suffering from terminal disease, the clinician should try to determine the patient's wishes regarding resuscitation (eg, intubation) either by asking the patient directly (assuming the patient retains capacity) or inquiring about an advanced directive (eg, "do not resuscitate" order). (See "Palliative care for adults in the ED: Concepts, presenting complaints, and symptom management".)

In cases where the need for a definitive airway is not immediately clear, a simple assessment consisting of three basic questions can distinguish patients requiring intubation from those who can be observed [1]. An affirmative answer to any of the following questions identifies the need for intubation in nearly all emergency scenarios (algorithm 1):

●Is patency or protection of the airway at risk?

●Is oxygenation or ventilation failing?

●Is a need for intubation anticipated (ie, what is the expected clinical course)?

IS PATENCY OR PROTECTION OF THE AIRWAY AT RISK? — A patient who can phonate clearly and answer questions appropriately demonstrates airway patency, adequate ventilation, vocal cord function, and cerebral perfusion with oxygenated blood. The level of alertness needed to maintain airway tone is the same required to maintain brisk protective reflexes to prevent aspiration of oral and gastric fluids. Aspiration of gastric contents can cause pneumonitis and result in prolonged mechanical ventilation [2,3].

The loss of protective airway reflexes mandates tracheal intubation. Traditional teaching promoted the presence of a gag reflex as evidence that protective reflexes were intact and aspiration would not occur. This is misleading and unfounded. The gag mechanism does not contribute to laryngeal closure and airway protection, and it has little correlation with the Glasgow Coma Scale (GCS). Furthermore, a sizable segment of the normal adult population lacks a gag reflex.

The ability to phonate and swallow secretions is a more reliable sign of the patient's capacity for airway protection than the gag reflex. While this concept has not been subjected to rigorous scientific evaluation, swallowing represents a higher level of neurologic complexity and more accurately represents a patient's ability to protect against aspiration. A patient with pooling secretions, unable to swallow, requires intubation.

Pulmonary gas exchange requires an unobstructed oropharyngeal inlet, which is maintained in awake patients by the upper airway musculature. An obstructed oropharynx makes any attempt to supply supplemental oxygen or assist ventilation difficult.

Basic airway maneuvers, such as repositioning the patient's head with a jaw-thrust or chin-lift, or placement of oropharyngeal and nasopharyngeal airways can bypass flaccid, redundant upper airway tissue and provide an unobstructed passageway to the laryngeal inlet and trachea. In general, patients who require an oral airway and tolerate its placement need intubation for airway protection. (See "Basic airway management in adults".)

IS OXYGENATION OR VENTILATION FAILING? — Human tissues depend on oxygen for cellular respiration. While anaerobic metabolism can maintain function for a short time in tissues such as skeletal muscle, most specialized tissues, especially neuronal and myocardial tissue, depend on oxygen and will sustain irreversible damage within a few minutes without an adequate supply of oxygenated blood. The inability to oxygenate despite supplemental oxygen poses an immediate life threat and, with rare exceptions, mandates intubation.

Advances in noninvasive positive-pressure ventilation (NIPPV) have modified the approach to hypoxic patients with acute cardiogenic pulmonary edema and acute exacerbations of chronic obstructive pulmonary disease (COPD). Often, NIPPV enables these patients to avoid intubation during the acute phase of their illness, but its use is limited to alert patients capable of protecting their airway against aspiration. The role of NIPPV in patients with other causes of acute respiratory distress remains unclear. NIPPV should not replace tracheal intubation in patients with severe respiratory distress or those who suffer from disease states that are unlikely to reverse quickly. (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)

Clinicians assess the patient's oxygenation using clinical criteria and oxygen saturation measurements. Clinically, hypoxic patients act restless and agitated, and with severe hypoxemia can appear cyanotic. As hypoxia worsens, confusion, somnolence, and obtundation occur. Patients are often tachycardic with mild to moderate degrees of hypoxia but exhibit profound bradycardia or agonal, non-perfusing rhythms with critically low oxygen saturations. Pulse oximetry provides an accurate estimate of arterial oxygen tension but can be unreliable when peripheral perfusion is compromised [4,5]. (See "Pulse oximetry" and "Measures of oxygenation and mechanisms of hypoxemia".)

Clinicians should not rely on arterial blood gases (ABGs) in the emergency setting to determine the immediate need for intubation. ABGs provide little information not already apparent from clinical presentation and pulse oximetry, and they can be misleading. As an example, an "unimpressive" ABG in a severe asthmatic may persuade the emergency clinician to postpone intubation when, clinically, the patient is failing. Waiting in such circumstances can be disastrous, creating an immediate need for intubation when the patient suddenly becomes apneic.

Removal of carbon dioxide (CO₂), the major waste product of cellular metabolism, depends on proper lung function and ventilation. Impaired ventilation from airway obstruction, muscular weakness, or drug-induced hypopnea results in impaired CO₂ elimination. Clinicians can generally gauge a patient's ventilations by observing respirations and mental status. Capnography provides a simple means of continuously measuring end-tidal CO₂ to assess the adequacy of ventilation, when this is not clear, or to monitor the response to treatment. (See "Carbon dioxide monitoring (capnography)".)

Patients with chronic ventilatory failure (eg, COPD) can acclimate to the altered gas tensions of impaired ventilation if decompensation is gradual, but acute CO₂ retention can lead to altered mental status and respiratory acidosis. Patients with inadequate ventilation require intubation, unless the cause is immediately reversible (eg, opioid overdose). In select patients with acute exacerbations of COPD, the use of continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BLPAP) may obviate tracheal intubation [6,7]. (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)

Despite advances in NIPPV, many patients, especially malnourished or dehydrated patients, fail trials of CPAP or BLPAP. Other patients present too ill for such measures to be effective, and intubation is needed. Continual reevaluation of patients treated with CPAP or BLPAP is required to detect clinical deterioration and provide definitive airway management if needed.

IS A NEED FOR INTUBATION ANTICIPATED? — Failure to maintain airway protection, oxygenation, or ventilation comprises straightforward criteria for intubation that encompasses the majority of emergency airway cases. However, some emergency patients require intubation even though there is no immediate threat to oxygenation or airway patency.

Often, acutely ill or injured patients initially appear awake and alert, speak clearly in full sentences, demonstrate adequate oxygen saturation, and appear not to require immediate airway management. Nevertheless, the natural progression of their disease would result in airway compromise or an inability to maintain oxygenation if the emergency clinician were not to intervene. By pursuing early, aggressive airway management, emergency clinicians avoid unplanned, hurried, or salvage airway situations, when equipment, medications, and personnel may not be ready. It is preferable to err on the side of caution and place a definitive airway if the potential for airway compromise exists.

As an example, an older adult patient with pneumonia and severe sepsis who is somnolent but arousable, with adequate oxygen saturation on supplemental oxygen, may not initially meet any of the criteria described above for tracheal intubation. Nevertheless, the patient's anticipated clinical course is a decline in respiratory function. During the resuscitative phase of sepsis management, the patient will receive intravenous isotonic fluids, antibiotics, and possibly blood products. This fluid load, coupled with a diffuse capillary leak syndrome, will increase pulmonary interstitial edema and likely lead to respiratory failure with worsening hypoxemia and acidemia.

As another example, the burn victim with evidence of significant smoke inhalation likely requires immediate intubation (or at least direct or fiberoptic examination of the upper airway structures and glottis) because the projected clinical course is complete airway obstruction, although the patient may initially manifest no sign of airway compromise. (See "Inhalation injury from heat, smoke, or chemical irritants".)

Patients with the potential for respiratory decompensation who must be transported out of the emergency department often require intubation. Regardless of whether transport is to the radiology department or to another institution for specialized care, it is better to secure the airway preemptively than to face an emergency unplanned airway in an unfavorable setting, such as a computed tomography scanner or the back of an ambulance. For trauma patients, intubation may be indicated before transport if the likelihood of deterioration is high based on mechanism, injuries discovered on primary and secondary surveys, and initial hemodynamics.

No guidelines or algorithms exist for this aspect of airway management, and there is no way to anticipate every possible scenario in which preemptive intubation is needed. A careful clinical assessment, including pulse oximetry (and often capnography), vital signs, the patient's mental and respiratory status, the patient's comorbidities and response to the acute threat, and a knowledge of the natural history of the condition with which the patient presents all guide the need for preemptive intubation. If there is any significant concern that a patient's deterioration will ultimately threaten the airway or make intubation more difficult, early intubation is indicated.

APPROACH TO THE PATIENT — When the patient is not comatose or in extremis, emergency clinicians assess the patient by asking three questions:

●Is patency or protection of the airway at risk?

●Is oxygenation or ventilation failing?

●Is a need for intubation anticipated (ie, what is the expected clinical course)?

The quickest test of airway patency and maintenance is to listen to the patient's speech. Clear, coherent speech is a good indication of a patent and protected airway and a reassuring sign that the airway is not in imminent danger.

If the patient is unable to phonate or his speech sounds altered, the clinician performs a rapid investigation for upper airway obstruction. A jaw-thrust and chin-lift, with cervical spine immobilization if indicated, is the first maneuver, followed by inspection of the oropharynx for solid or liquid material that can be removed or suctioned. The neck is inspected and palpated for fixed or expanding masses, laryngeal fracture, and crepitus. Stridor is a foreboding sign indicating impending airway occlusion, and immediate intubation is required. If these maneuvers do not identify the problem and the patient remains unable to phonate and protect his airway, intubation is performed. As part of the airway examination, clinicians assess whether a difficult airway exists. (See "Approach to the difficult airway in adults for emergency medicine and critical care".)

Assessment of oxygenation and ventilation status is predominantly clinical. Hypopnea, poor chest excursion, agitation or somnolence, and low oxygen saturation by pulse oximetry generally provide all the data required. Capnography can provide important information about ventilation, respiratory status, and response to treatment. (See "Pulse oximetry" and "Carbon dioxide monitoring (capnography)".)

Overall patient condition may dictate intubation, even if no specific criteria are met. All potentially unstable patients requiring prolonged emergency department evaluation or transport to other facilities are candidates for early airway management. This anticipatory step provides safer patient care because it helps to reduce the likelihood of a chaotic "crash" intubation.

SUMMARY AND RECOMMENDATIONS

●Approach to deciding to intubate – When the need for intubation is unclear, emergency clinicians assess the patient by asking three questions. An algorithm incorporating these questions is provided (algorithm 1). An affirmative answer to any of the following questions identifies the need for intubation in nearly all emergency scenarios (see 'Deciding to intubate: Three-question assessment' above):

•Is patency or protection of the airway at risk?

•Is oxygenation or ventilation failing?

•Is a need for intubation anticipated (ie, what is the expected clinical course)?

●Assessing airway protection – The gag reflex has no role in determining the need for intubation or the patient's ability to protect their airway. The gag mechanism does not contribute to laryngeal closure and airway protection, and a sizable segment of the normal adult population lacks a gag reflex. The ability to swallow secretions is a more reliable sign of the patient's capacity for airway protection than the gag reflex. (See 'Is patency or protection of the airway at risk?' above.)

●Assessing oxygenation and ventilation – Assess the patient's oxygenation using clinical criteria and oxygen saturation measurements. Clinicians can generally gauge a patient's ventilations by observing respirations and mental status. Capnography provides a simple means of continuously measuring end-tidal carbon dioxide to assess the adequacy of ventilation (when unclear) or to monitor the response to treatment. Clinicians should not rely on arterial blood gases (ABGs) in the emergency setting to determine the immediate need for intubation. (See 'Is oxygenation or ventilation failing?' above.)

Noninvasive positive-pressure ventilation (NIPPV) often enables patients with acute cardiogenic pulmonary edema and acute exacerbations of chronic obstructive pulmonary disease (COPD) to avoid intubation acutely, but its use is limited to alert patients capable of protecting their airway against aspiration. NIPPV should not supplant intubation for patients with severe respiratory distress requiring immediate tracheal intubation. (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)

●Anticipating need for intubation – Despite the absence of overt signs of respiratory distress, some patients need early intubation because of their anticipated clinical course, particularly the possibility of respiratory decompensation when outside the emergency department or the progression of upper airway obstruction. (See 'Is a need for intubation anticipated?' above.)