Mount Sinai Expert Guides. Группа авторов
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 positioning creates a direct line of sight from the patient’s mouth to the larynx. This is accomplished using approximately 30° of cervical flexion using pillows/blankets along with extension of the atlanto‐occipital joint, the classic ‘sniffing position.’
Positioning obese patients may be particularly challenging. This can be accomplished by forming a ramp, elevating the upper back and shoulders in order to accommodate adequate cervical flexion. Confirming horizontal alignment of the external auditory meatus with the sternal notch can be a useful guide.
Preoxygenation
Adequate preoxygenation should be provided in all but the most emergent situations.
The aim is to replace nitrogen in the lungs with oxygen. This increases the length of time before desaturation when the patient is apneic (‘apnea time’), providing a margin of safety in case ventilation and intubation become difficult.
Preoxygenation can be performed using a facemask, continuous or bilevel positive airway pressure, or a high flow nasal cannula (HFNC) providing 100% oxygen at flows of at least 10 L/min. It typically requires approximately 3 minutes of normal tidal volume breathing to achieve an end‐tidal oxygen concentration of approximately 90%.
Given normal functional residual capacity (FRC) of about 2 L, and an oxygen consumption rate of about 200–250 mL/min, a properly preoxygenated adult should have an apnea time of about 5–8 minutes before significant desaturation. Reductions in apnea time should be expected in conditions in which FRC is decreased (i.e. obesity, pregnancy, tense ascites) or conditions of increased oxygen consumption (i.e. sepsis, pregnancy, hyperthyroidism).
Bag and mask ventilation
The ability to ventilate a patient using a bag and mask is by far the most important skill for any airway provider to master. The inability to intubate the trachea is not fatal if mask ventilation is possible, making it a vital component of the ASA difficult airway algorithm.
Relative contraindications to mask ventilation are full stomach/regurgitation risk, severe facial trauma, and unstable cervical spine fractures.
Mask