Certain indications for intubation in the neurocritically ill are similar to other patient cohorts (ie, failure to maintain or protect the airway or failure of oxygenation and or ventilation).¹ The indications for immediately securing the airway in our specific patient include the following:

1. 
   

   This patient is a state of acute neurologic decline with a worsening neurologic examination.

   
   
2. 
   

   He has dangerously dulled airway protective reflexes and is considered to have a full stomach, putting him at risk for large-volume gastric aspiration.

   
   
3. 
   

   He will likely require additional invasive procedures with sedation (eg, external ventricular drain, intracranial pressure (ICP) monitor placement, or craniotomy).

   
   
4. 
   

   He will be transported between units and likely will undergo further imaging studies, requiring supine positioning.

Airway considerations and challenges specific to the neurocritically ill include the following:

1. 
   

   The need to perform serial neurologic examinations makes intermediate- and long-acting sedation and neuromuscular blockade fundamentally undesirable.

   
   
2. 
   

   Hypoxemia is a potent mediator of secondary brain injury and must be avoided.

   
   
3. 
   

   In patients with ischemia-reperfusion, such as cardiac arrest, ischemic stroke, and sometimes traumatic brain injury (TBI), hyperoxia (such as occurs when 100% Fio₂ is administered to a patient with good cardiopulmonary function) should be avoided: it potentiates reperfusion injury and is associated with worse outcomes.

   
   
4. 
   

   Hyperventilation increases cerebrovascular tone, acutely decreasing cerebral blood flow, with implications on maintaining cerebral perfusion and managing ICP.

   
   
5. 
   

   Hypoventilation decreases cerebrovascular tone, increasing cerebral blood volume and acutely driving up ICP.

   
   
6. 
   

   In neurotrauma, head and facial trauma can create upper airway obstruction, and there is a high incidence of cervical spine injury and instability, placing the cervical spinal cord at risk during intubation and other airway maneuvers.

   
   
7. 
   

   Patients with acute ischemic stroke are exquisitely sensitivity to changes in hemodynamics, such as the blood pressure drop seen with propofol administration, the vasoconstriction related to hyperventilation, and the failure of physiological shunting to an ischemic region after administration of vasodilators such as nitrates or calcium channel blockers.

   
   
8. 
   

   In patients with elevated ICP, a critical drop in cerebral perfusion pressure (CPP) can occur with induction and the loss of sympathetic tone, leading to ischemia and herniation.

   
   
9. 
   

   Patients with injury to the lower pons or medulla and those with elevated ICP (especially in the posterior fossa) or uncontrolled seizures may have unstable central ventilatory drive and are at risk of respiratory arrest.

Is it appropriate to intubate every patient with abnormal airway protection? No, although in the acute phase of a neurologic injury, endotracheal intubation is often indicated and may be lifesaving. When considering intubation, clinicians should consider two questions: is the patient at risk of respiratory arrest due to failed central respiratory drive (see item 9 above) and can they maintain the airway?

Airway maintenance involves an unobstructed upper airway for adequate gas exchange and adequate “airway protective mechanisms,” the details of which remain controversial, in part because of their complexity. Airway obstruction comes into play in patients with obstructive sleep apnea, unfavorable oropharyngeal anatomy, or severe bulbar dysfunction related to brainstem compromise. These patients fail because the airway must be maintained open during airflow, a process involving activation of pharyngeal dilator muscles, and closed to prevent penetration of secretions and food particles into the lower respiratory tract when airflow ceases. Cyclic upper airway obstruction such as occurs in sleep-disordered breathing results in erratic fluctuations in ventilation, oxygenation, blood pressure, sympathetic nervous tone, and both intrathoracic and interabdominal pressures, which increase the risk of reflux and large-volume aspiration.

A normal airway protective mechanism involves the following:

1. 
   

   Opening of the larynx, vocal folds, and vocal cords during inspiration and expiration (including speech), closure when airflow stops, and then mechanical separation of the airway and digestive tract during swallowing

   
   
2. 
   

   Coordinated oropharyngeal sensory and muscle activity to move swallowed secretions, liquids, or food in a posterior and inferior direction (away from the larynx) into the upper esophagus, while the larynx moves in an anterior and superior direction and the rapid activation of esophageal peristalsis clears the oropharynx

   
   
3. 
   

   A tight lower esophageal sphincter and low gastric pH

   
   
4. 
   

   Elevation and anterior displacement of the glottis during swallowing, with tight closure and approximation of vocal cords and folds

   
   
5. 
   

   A robust sensory response to solids and liquids at the glottis and lower airways, as well as intact cough centers and efferent nervous pathways to the effector muscles

   
   
6. 
   

   Adequate respiratory muscle strength and tidal volume to generate a strong cough

   
   
7. 
   

   Healthy bronchial epithelium with intact villi that clear foreign substances from the smaller, distal airways

Patients with incomplete or failed airway protective mechanisms are at high risk of aspirating food, secretions, and gastric contents. A clinically unstable patient with impaired airway maintenance requires intubation, whereas a clinically stable patient with impaired airway maintenance can often be managed without an endotracheal tube by careful feeding (often through an enteral feeding tube) and attentive nursing, speech-language pathology, and respiratory care.

Routinely applied airway assessment measures include the Glasgow Coma Scale (GCS) score, strength of cough, quantity and character of oral and respiratory secretions, and an evaluation of oropharyngeal coordination and sensation. An airway protection score has been proposed to evaluate for risk of aspiration (Table 41-1).^2,3 Assessment of the gag reflex is routine, but does not correlate well with laryngeal closure and airway protection,^4,5 and may be absent in up to 37% of healthy subjects.⁶

In the acute setting, a GCS score ≤ 8 has been described as both sensitive and specific for predicting the need for endotracheal intubation,⁷ applied not only in trauma, but in patients with stroke, intoxication, and other etiologies of altered mental status.¹ Several studies have demonstrated that patients with a GCS ≤ 8 have airway obstruction and are at significant risk of hypoxemia and hypoventilation,⁸ resulting from pooled secretions, anatomic compression, or foreign-body aspiration. Although GCS is routinely employed in the emergency department and by emergency medical services (EMS) as part of a triage process to assess patients for intubation, the GCS was not developed for this purpose and does not address many of the primary issues related to airway protection: cough, the ability to manage secretions in the upper airway, or the acuity or anticipated course of the primary neurologic process. Table 41-2 summarizes oxygen delivery devices and actual tracheal oxygen delivery.

Aspiration before or during intubation can lead to fever, pneumonia, acute respiratory distress syndrome (ARDS), and systemic inflammation, each associated with worse neurologic outcomes and increased mortality. These concerns, which suggest that intubation may be required for many acutely ill neurologic patients, are balanced by the principles of preserving an accurate neurologic examination and avoiding the complications of intubation and mechanical ventilation whenever possible.

Unfortunately, there is no single element of airway assessment that uniformly predicts a challenging airway.⁹ Hence we use a composite of multiple elements to develop a risk profile.

The anatomic evaluation of the airway is comprised of several elements of which the most commonly used assessments are described below:

1. 
   

   Assessment of the oropharyngeal space: The Mallampatti classification has stood the test of time as a useful evaluation of the airway. In essence it describes the oropharyngeal space with respect to size of the tongue.

   
   
2. 
   

   Assessment of neck extension: Normal neck extension in the supine position is > 35°. This assesses the ability to maintain the “Sniffing position” or anatomically to align the axes of the airways (oral, pharyngeal, and laryngeal) during direct laryngoscopy (DL). This is the basis of the three axes alignment theory (TAAT).

   
   
3. 
   

   Assessment of the submandibular space: This is a crucial anatomic compartment because it is the space the tongue is displaced into during laryngoscopy. The thyromental distance (TMD) is defined as the distance from the mentum to the thyroid notch while the patient’s neck is fully extended. This is usually > 3 finger breaths or > 6 cm. When this distance is < 6 cm, the glottis on laryngoscopy tends to be anteriorly placed. The sterno-mental distance: the distance from the sternal notch to the mentum measured in the neutral position. This is normally > 12 cm.

   
   
4. 
   

   Upper lip bite test (ULBT): This is a relatively recent maneuver described to screen for difficult laryngoscopy. The test evaluates the patient’s ability to reach or completely cover the upper lip with the lower incisors. Grade I (the lower incisors can fully cover the upper lip’s mucosa) and grade II (the lower incisors can touch the upper lip but cannot fully cover the mucosa) are thought to predict easy laryngoscopy and are compared with grade III of the ULBT (the lower incisors fail to bite the upper lip) that was found to be associated with difficult laryngoscopy.¹⁰

   
   
5. 
   

   Neck circumference: Neck circumference at the level of the thyroid cartilage is a valuable predictor of difficult laryngoscopy, especially in obese patients. Men: > 43 cm (17 in) and women: > 37 cm (15 in).¹¹

   
   
6. 
   

   Others: Other described anatomic measurements include the inter-incisor distance (normal > 4 cm), mandibulo-hypoid distance (mostly replaced by the TMD).

Airway evaluation should be performed on every patient requiring airway management. For the patient requiring tracheal intubation, an airway evaluation is performed primarily to help decide if intubation can be safely performed after the induction of general anesthesia (with or without maintenance of spontaneous ventilation) or if intubation should proceed with the patient awake.

There are several prediction scores and criteria that have been described in the past for prediction of difficult airways, including the Wilson score, but frequently their routine use is unclear. Careful attention should be given to identifiable predictors of difficult mask ventilation as well as those associated with difficulty in intubation (Tables 41-3 and 41-4).

The simple acronym OBESE (O: obese with body mass index [BMI] > 26 [in kg/m²]; B: Bearded; E: Elderly, > 55 years; S: Snorer; and E: Edentulous) can alert the user to the possibility of difficult mask ventilation. This acronym has a sensitivity of 72% and specificity of 73%.¹² Difficult mask ventilation is more dangerous than a difficult intubation, because even if intubation attempts were to fail, oxygenation can be maintained indefinitely in a ventilatable patient.

Similarly, the LEMON score has been developed to aid objective assessment of the possible difficult intubation. This was developed primarily in the emergency department population but is applicable elsewhere as well.¹³ Although the original tool included the Mallampati score, this is often not useable in emergent circumstances and a modified version has been proposed that drops the Mallampati element:¹²

1. 
   

   Look externally. There may be some physical clue or foreign object that portends difficulty.

   
   
2. 
   

   Evaluate using the 3-3-2 rule: (a) inter-incisor distance: 3-finger breadth; (b) thyromental distance: 3-finger breadth; and (c) thyro-hyoid distance: 2-finger breadth.

   
   
3. 
   

   Mallampati evaluation: may not always be possible in the neurocritical care population.

   
   
4. 
   

   Obstruction: soft tissue swelling, eg, from smoke inhalation, trauma to the face or neck, foreign bodies in the airway, and excessive soft tissue from obesity.

   
   
5. 
   

   Neck mobility: any limitations in extension.

There are almost an overwhelming number of choices for devices to help with emergency airway management. Like any nontraditional method of laryngoscopy, any of the devices and adjuncts mentioned below require objective skill acquisition and maintenance to be used effectively in an urgent or emergent situation. Important techniques for managing difficult airways include the use of special equipment designed to facilitate placement of the endotracheal tube (ETT), placement of temporizing airway devices, and surgical airways. Some of these devices are summarized in Table 41-5. Each of them has specific indications and situations where they are less useful. Some of the common devices are summarized below.

Specialized equipment and techniques to facilitate endotracheal intubation can be broadly categorized into the following:

1. 
   

   Modified or specialized laryngoscope blades: There are more than 50 types of laryngoscope blades (eg, Macintosh, Miller, Wisconsin, Wis-Hipple, Guedel straight blade).

   
   
2. 
   

   Types of laryngoscopes

   
   
   
   
   • 
     

     Conventional laryngoscopes, Patil-Syracuse laryngoscope (flexible handle that can be locked in 4 different angles: 180°, 135°, 90°, standard or 45° (Howland Lock Angle).

     
     
   • 
     

     Optical laryngoscopes: these modified laryngoscopes have a viewfinder that allows for visualization of the glottis. The optical quality is less true than with the fiberoptic based video laryngoscopes but is still a very useful and less expensive option. Truview laryngoscope and the Airtraq optical laryngoscope are good examples.

     
     
   • 
     

     Video laryngoscopes: Glidescope, LMA McGrath, King vision scope. Airtraq is a single-use rigid optical laryngoscope.

   
   
3. 
   

   Endotracheal tube introducers: These adjunct devices enable navigating a rigid guide into the glottis and then “rail-roading” the endotracheal tube over it. These include gum-elastic “bougie,” Coude tip bougie, Aintree intubation catheter, Eschmann stylet, and light wands

   
   
4. 
   

   Supraglottic airways: The most common device is the laryngeal mask airway (LMA), a modified oral airway designed as an inflatable latex mask placed blindly into the hypopharynx and positioned above the glottis opening. Although not considered a “definitive” airway, it offers the advantage that requires minimal experience to competently employ and may be extremely helpful if a skilled intubator is not available in an urgent situation. However, it does not protect against aspiration. The original LMA has undergone multiple generations of modifications and specializations including the intubating LMA, Air Q (designed to facilitate fiberoptic intubation through it with conventional endotracheal tubes), LMA Proseal (allows for aspiration of gastric contents), LMA supreme, and the iGel, an LMA variant with a gel-like, noninflatable cuff designed to provide an anatomical, impression fit over the laryngeal inlet.

   
   
5. 
   

   Devices designed for blind insertion: Combitube (dual inflation, dual balloon design), King LT airway (single inflation, dual balloon dual design). These devices offer the advantage of enabling an airway to ventilate through, but it also occludes the esophagus, preventing gastric inflation and aspiration. They are used primarily by EMS personnel in the field, and as part of emergency airway management kits elsewhere.

   
   
6. 
   

   Lighted stylets and optical stylets: devices such as the Trachlight depend on the transillumination of light through the anterior aspect of the neck to providing indirect visual confirmation of tracheal placement. This device does not require visualization of the glottis for use. The optical stylets have fiberoptic or video viewing element incorporated into the distal end of a metal stylet: Clarus Video System, Shikani Optical Stylet, Bonfils Retromolar Intubation Fiberscope, Levitan FPS Scope

   
   
7. 
   

   Flexible fiberoptic endoscope: an indispensable tool for difficult airway management when one has to avoid general anesthesia and neuromuscular blockade in a patient for any reason. Fiberoptic intubation provides a reliable method of managing an airway with minimal distraction injury to the spinal cord. The fiberoptic scope can be coupled with other devices to aid endotracheal intubation as well. It is worth noting that this is not ideal in emergent circumstances and when there is significant amount of blood in the oropharynx and airways.

   
   
8. 
   

   Surgical airway management: cricothyrotomy (needle, wire-guided or surgical) is the emergent surgical procedure to save a patient’s life in a “cannot ventilate and cannot intubate” scenario. A tracheostomy is a more complex and time-consuming procedure and should generally be reserved for nonemergent situations (see Chapter 46, Bronchoscopy in the NeuroICU).