and muscles. The thyroid cartilage functions partly to shield the vocal cords. Inferior to the cricoid cartilage lies the trachea, which extends to the carina at approximately T5 where it branches into the right and left mainstem bronchi. The right mainstem bronchus takeoff is more straight and vertical, making it the most likely path taken by a deep endotracheal tube placement.
Innervation of the upper airway is from the cranial nerves. Sensation to mucous membranes of the nose is supplied by the ophthalmic division (V1) of the trigeminal nerve anteriorly and the maxillary division of the same nerve posteriorly. The glossopharyngeal nerve provides sensation to the posterior third of the tongue as well as the tonsils and undersurface of the soft palate.
Below the epiglottis, sensation is supplied by branches of the vagus nerve. The superior laryngeal branch divides into external and internal segments. The internal branch provides sensation to the larynx between the epiglottis and the vocal cords. Another branch of the vagus nerve, the recurrent laryngeal nerve, provides laryngeal sensation below the vocal cords as well as the trachea.
Motor supply to the muscles of the larynx is from the recurrent laryngeal nerve, with the exception of the cricothyroid muscle (vocal cord tensor), which is innervated by the external branch of the superior laryngeal nerve. All vocal cord abductors are controlled by the recurrent laryngeal nerve.
Airway assessment
Complete airway assessment includes taking a history and a physical examination, noting any findings indicative of possible difficulty with mask ventilation, endotracheal intubation, or both.
While airway management in the ICU can often be urgent or even emergent, failure to recognize predictors of a difficult airway can have potentially dire consequences.
The most likely predictor of airway difficulty is a history of previous difficulty. Other ‘red flags’ include a history of head and/or neck radiation, airway or cervical spine surgeries, obstructive sleep apnea, presence of a mediastinal mass, or certain chromosomal abnormalities or inherited metabolic disorders.
Time of last oral intake should be determined, if at all possible, as clear liquids within 2 hours or solid meals within 8 hours put the patient at higher risk for aspiration. Other risk factors for aspiration include gastroesophageal reflux disease (GERD), hiatal hernia, pregnancy, diabetes (gastroparesis), and morbid obesity.
Physical examination should include assessment of the oral cavity as well as external characteristics of the head and neck, again noting potential difficulties with mask ventilation and/or intubation (Table 1.1).
Mouth opening, presence of facial hair, and presence or absence of teeth/dentures should be assessed. Any loose teeth should be noted and dentures should be removed to avoid dislodgment and potential aspiration.
The Mallampati classification describes the size of the tongue in relation to the oral cavity, which is a clinical sign developed to aid in the prediction of endotracheal intubation difficulty. The test is traditionally performed on a seated patient with the head in a neutral position, mouth opened, with the tongue protruding with no phonation. Scores are assigned based on the visibility of the oropharyngeal structures. A Mallampati class I score is indicative of relatively easy endotracheal intubation while a score of IV suggests the possibility of difficult intubation when taking other clinical signs into account (Figure 1.1).
Examination of the neck should note any masses or goiters as well as tracheal deviation from the midline. One should note neck circumference, the ability to flex and extend the neck, as well as thyromental distance.
Table 1.1 Predictors of difficulties with mask ventilation and/or intubation.
| Predictors of difficult mask ventilation | Predictors of difficult laryngoscopy |
|---|---|
| Edentulous | Overbite |
| Age 55 years or older | Small mouth opening <3 cm |
| Male patient | Mallampati class III or IV |
| Presence of facial hair | Thyromental distance <3 fingerbreadths |
| Obesity | Neck circumference >43 cm (17 inches) |
| Obstructive sleep apnea | Limited cervical mobility |
Equipment
Proper preparation is essential for all airway management situations.
Essential equipment includes oxygen source (wall or tank), suction, bag‐mask ventilation circuit, direct and/or video laryngoscopes, endotracheal tubes of several sizes, supraglottic airway device, blood pressure/ECG/pulse oximetry, and CO2 detection device.
Supraglottic airway devices include the laryngeal mask airway (LMA) which is inserted into the patient’s mouth and sits above the glottis. As these devices do not protect against aspiration of gastric contents, in the ICU they are generally limited to rescue devices in situations where mask ventilation and endotracheal intubation are difficult.
While numerous types of direct laryngoscopes are available, the two most common are the Macintosh blade (MAC) and the Miller blade. Both come in multiple sizes, but typically a MAC 3 or Miller 2 are suitable for a standard‐sized adult.
In recent years, video laryngoscopes, a form of indirect laryngoscopy, have become readily available in most institutions. Video laryngoscopes differ from one another in the shape of the blade, proper position when inserted into the mouth, location of the video source, and reusable/disposable parts. Glidescope® has its own (non‐disposable) stylet which accompanies the unique shape of its blade. One potential problem with video laryngoscopy is that, while it may provide a clear view of the glottic opening, one still may have difficulty maneuvering an endotracheal tube into proper position.
Endotracheal tubes (ETTs) are also available in various materials and sizes. Most commonly used in the ICU are ETTs made from polyvinyl chloride with a beveled tip to allow better visualization of insertion, a side hole (Murphy’s eye) to prevent total occlusion in the event of a mucous plug, and an inflatable cuff. ETTs are sized according to internal diameter in millimeters and the appropriate size for adults is typically 7.0–8.0 mm. Bear in mind that if bronchoscopy is needed, ETTs smaller than 7.5 mm may be too narrow to accommodate an adult bronchoscope.
Positioning
Proper patient positioning is of utmost importance and should be achieved prior to any airway intervention, particularly if direct laryngoscopy is to be attempted. Proper positioning can be the difference between a successful and unsuccessful laryngoscopy attempt.
With the provider standing at the head of the bed, the patient’s head should be as far towards the head of the bed as possible. The height of the bed should be to the provider’s preference.
Proper
