Airway Management

Question 1

Describe the anatomy of the upper and lower airway.

Answer 1

The upper airway consists of the nose, mouth, pharynx, larynx, and the lower airway, the tracheobronchial tree. The two openings to the upper airway (nose and mouth) are separated anteriorly by the palate and connected posteriorly by the pharynx. The pharynx connects the nose and mouth to the larynx and esophagus. A cartilaginous structure at the base of the tongue, known as the epiglottis, protects the opening of the larynx, known as the glottis, against aspiration with swallowing (Fig. 3.1).
Below the epiglottis lies the larynx, commonly known as the voice box. The larynx is a cartilaginous structure that houses and protects the vocal folds, which enable phonation. The inferior border of the larynx is defined by the cricoid cartilage, which is the only complete cartilaginous ring of the tracheobronchial tree. Below the cricoid cartilage is the lower airway, which contains the trachea and mainstem bronchi, which lead to the left and right lungs.

Question 2

Describe the sensory innervation of the upper and lower airway.

Answer 2

The mucous membranes of the nasal passages are innervated by the ophthalmic division of the trigeminal nerve (V1) anteriorly, and the maxillary division of the trigeminal nerve (V2) posteriorly.

The palatine nerves (consisting of V1 and V2) supply the soft and hard palate separating the oral and nasal passages.

The lingual nerve (the mandibular branch of trigeminal nerve) and the glossopharyngeal nerve provide sensation to the anterior two-thirds and posterior one-third of the tongue, respectively.

The glossopharyngeal nerve also provides sensory innervation to the tonsils, pharyngeal roof, and parts of the soft palate.

Branches of the vagus nerve provide sensory innervation to the upper airway below the epiglottis.
The superior laryngeal nerve provides sensory innervation between the epiglottis
and larynx,
whereas the recurrent laryngeal nerve provides sensory innervation between the larynx and trachea.

Question 3

What components of the patient history are important in airway evaluation during the preoperative assessment?

Answer 3

Because airway management complications remain the single most common cause of morbidity and mortality attributable to anesthesia, a proper and thorough assessment of a patient’s airway is a key component of the preoperative workup. -Previous anesthetic records, if available, can provide information about airway management problems in the past, including mask ventilation, intubation, and special airway techniques or equipment required for successful airway management. It is also important to ask the patient about prior anesthetics, as this may provide important information that could alert the practitioner to have additional personnel or airway management equipment immediately available.

• In addition, during the history, it is important to inquire about previous medical interventions or trauma that may have implications on airway management such as:
  (1) cervical spine injury or surgery,
  (2) history of tracheostomy,
  (3) head and neck surgery,
  (4) head and neck radiation treatment,
  (5) congenital craniofacial abnormalities, and
  (6) predisposition to atlantoaxial instability (e.g., rheumatoid arthritis, achondroplasia, Down syndrome).

Question 4

What components of the physical examination are important in airway evaluation during the preoperative assessment?

Answer 4

A proper physical examination of the airway should
-begin with a general inspection of the patient’s physical appearance. Important things to note include morbid obesity, frailty, and mental status.
-This should be followed by gross inspection of the face and neck for anything suggestive of a difficult airway.
Several features that are suggestive of a potentially difficult intubation include:
(1) short neck,
(2) inability to fully flex and/or extend the neck,
(3) large neck circumference (>42 cm),
(4) evidence of prior operations (especially tracheostomy), and
(5) abnormal neck masses (including but not limited to tumor, goiter, hematoma, abscess, or edema).
-Next, attention should be paid to the mouth. Concerning features include:
small mouth opening (interincisor distance <3 cm),
large tongue,
micrognathia or undersized jaw,
short thyromental distance (<3 finger breadths),
Mallampati score of III or IV, and
inability to bite the upper lip.

-It is also important to examine the patient’s dentition. Teeth that are chipped, missing, or loose should be documented. If the case is elective, and there is high risk for tooth dislodgement, it may be prudent to have the patient see a dentist for extraction before the case. Dental appliances that are loose or easily removable should be removed before anesthesia, as they can impede airway management or pose an aspiration risk.
If the patient is edentulous, direct laryngoscopy and intubation may be easier, but mask ventilation may prove more challenging.

Question 5

What are the predictors of difficult mask ventilation?

Answer 5

(1) presence of a beard,
(2) lack of teeth,
(3) obstructive sleep apnea or snoring history,
(4) age over 55 years, and
(5) obesity

Question 6

What is the Mallampati classification?

Answer 6

The Mallampati classification system is a scoring system used to predict the difficulty of intubation when combined with other features of the airway examination that are suggestive of a difficult intubation (Fig. 3.2).
A score of III or IV means the patient is at higher risk of being a difficult intubation. To assess Mallampati classification,
a patient must be sitting upright with the head neutral, mouth open, tongue protruded, and not phonating. A score of I to IV is assigned based on which structures are visible:

I. Tonsillar pillars, uvula, and soft palate
II. Base of uvula and soft palate
III. Soft palate only
IV. Hard palate only

Question 7

What are the general indications for endotracheal intubation? How does this apply to general anesthesia?

Answer 7

There are three main indications to intubate a patient:

1) Inability to protect airway (e.g., altered mental status)
2) Hypercapnic respiratory failure (e.g., chronic obstructive respiratory disease)
3) Hypoxemic respiratory failure (e.g., acute respiratory distress syndrome)

Hemodynamic instability is also an indication for intubation, particularly in the setting of cardiac arrest, but
this is primarily because of altered mental status caused by hypotension, which may lead to aspiration (inability to protect airway) and/or upper airway obstruction leading to hypoventilation.
Patients under general anesthesia are primarily intubated for airway protection to prevent aspiration. Although general anesthetic agents and opioids suppress respiratory drive and can cause hypercapnic respiratory failure, this unto itself is not an absolute indication for endotracheal intubation, as mask ventilation or placement of a supraglottic airway can treat temporary hypercapnic respiratory from general anesthesia in short surgical operations (i.e.,
1–2 hours). In summary, patients under general anesthesia are primarily intubated for airway protection and secondarily because of hypercapnic respiratory failure.

Question 8

What equipment should I have available when planning to intubate a patient?

Answer 8

One must ensure that the necessary medications and equipment (including backup devices), are available, accessible, and in working order. It is also critically important to have awareness of who is available for assistance and how those individuals can be contacted in the event of an emergency.
Medications that will be used for the induction of anesthesia should be drawn up in preparation for endotracheal intubation. In addition, emergency medications, including vasopressors for hemodynamic management and short acting paralytics (i.e., succinylcholine), should readily be available.
The patient should be attached to standard American Society of Anesthesiologists monitors (i.e., blood pressure, pulse oximeter, electrocardiogram) before induction of anesthesia and end-tidal CO2 (ETCO2) monitoring and a stethoscope should be available to confirm correct endotracheal tube placement, following intubation. A ventilator or anesthesia machine should also be available, but importantly, a standard bag-valve-mask (Ambu bag) should be immediately available to allow for mask ventilation if intubation proves difficult and to serve as backup in case of ventilator machine failure.
Specific airway management equipment should include:
• Appropriately fitting mask
• Direct laryngoscope, video laryngoscope, or flexible intubating scope
• Endotracheal tube (in multiple sizes)
• Lubricant
• Oral and/or nasal airways
• Adhesive tape
• Tongue depressor
• Suction
• Supraglottic airway (e.g., laryngeal mask airway [LMA])
• Bag-valve-mask device
• Oxygen source

Question 9

What is the purpose of preoxygenation before the induction of anesthesia?

Techniques in doing your pre-oxygenation?

Answer 9

The goal of preoxygenation before induction of anesthesia is to increase the safe apnea time before intubation. Safe apnea time is defined as the duration of time after cessation of breathing or ventilation, until arterial oxygen levels begin to decrease below a critical value (i.e., pulse oximetry [SpO2] <90%). Because of the steep slope of the oxygen-hemoglobin dissociation curve, oxygen desaturation will quickly drop below this critical value. During preoxygenation, when the patient inhales 100% oxygen (rather than 21% oxygen contained in room air), he or she is removing nitrogen from the lungs (a process known as denitrogenation) and filling the functional residual capacity (FRC) of the lungs with 100% oxygen. FRC is formally defined as the summation of expiratory reserve volume and residual volume and is the resting lung volume in an apneic patient, following induction of anesthesia. When the FRC is full of 100% O2, safe apnea time is increased roughly fivefold compared with a patient
breathing room air (100% is roughly 5 times > 21%).

Question 10

What techniques can be used to effectively mask ventilate a patient?

Answer 10

Mask ventilation is a skill that is easy to learn but takes practice to master. To successfully mask ventilate, pay careful attention to ensure the mask overlies both the oral and nasal openings to allow for an adequate seal between
the mask and patient’s face. This enables the provider to generate positive pressure for ventilation. Without this seal, the anesthesia reservoir bag may not inflate, and it is difficult to deliver positive pressure breaths.
The provider may use the left hand only (most common technique) or two hands (in more challenging airways) to hold the mask and apply it to the patient’s face. Subsequently, the provider should lift the patient’s face into the mask by thrusting the mandible forward, using the third, fourth, and fifth fingers (resembles the shape of an “E”). Mandibular protrusion pulls the tongue and epiglottis anteriorly to promote airway patency. Next, the first and second fingers should press the mask to the face (resembles the shape of a “C”) to create a seal. It is often helpful to extend the head as well, which straightens the upper airway reducing turbulent flow.

Question 11

What is a rapid sequence induction of anesthesia and intubation?

Answer 11

Rapid sequence induction of anesthesia and intubation (RSII), more commonly referred to as rapid sequence induction (RSI), is an established method to rapidly secure an airway with an endotracheal tube in a patient who is at increased risk of aspiration. RSI frequently involves the following components:
1) Rapid injection of anesthetic agents and a rapid onset paralytic (i.e., succinylcholine or double dose rocuronium)
2) Avoidance of mask ventilation and immediate laryngoscopy and intubation, following induction
3) An assistant to provide cricoid pressure (CP) to block gastric contents from moving up the esophagus, into the pharynx, and into the tracheobronchial tree
4) Avoidance of other medications before induction of anesthesia that can precipitate aspiration, such as benzodiazepines or opioids
Although the avoidance of aspiration is the primary indication for RSI, preventing hypoxia is paramount. In
general, it is important to avoid mask ventilation when performing an RSI to minimize gastric insufflation, which can also increase the risk of aspiration itself. However, if necessary, mask ventilation can be performed if hypoxemia ensues and the provider is unable to intubate ideally with CP being applied (modified RSI).

Question 12

What patients are at risk of aspiration?

Answer 12

RSI is used to minimize the risk of aspiration in several clinical situations, including:
• Emergent intubation in acutely ill patients or in patients whose nothing-by-mouth status cannot be confirmed
• Pregnancy
• Acute intraabdominal process, particularly small or large bowel obstruction but also should be considered in
appendicitis or cholecystitis
• Delayed gastric emptying (i.e., trauma, alcohol or opioid use, end-stage renal disease, poorly controlled
diabetics)
• Active or recent vomiting
• Patients who have not adequately fasted (>8 hours for food and >2 hours for clear liquids)
• Severe gastroesophageal reflux disease

Question 13

What is cricoid pressure? Does it work?

Answer 13

CP involves applying pressure to the cricoid cartilage to minimize the risk of aspiration when performing an RSI.
It is thought to work by compressing the esophagus; however, one magnetic resonance imaging study showed that it compresses the hypopharynx and not the esophagus per se. The efficacy of CP is debated, particularly as CP
can worsen the view on laryngoscopy. It is in the author’s opinion to recommend CP, as it can easily be aborted if it interferes with intubation. CP is generally applied before induction of anesthesia and released following confirmation of ETCO2, after successful intubation.

Question 14

What is sniffing position?

Answer 14

Sniffing position is a method to align the upper and lower airway axes to facilitate direct laryngoscopy, allowing for a direct line of site to the glottic opening hence the term direct laryngoscopy. This involves cervical flexion
and atlantooccipital extension or more simply put, “head extension and neck flexion” (Fig. 3.3). The patient is said to be in sniffing position if an imaginary line from the external auditory meatus to the sternal notch is parallel to the floor.
Relative contraindications to sniffing position include atlantoaxial instability (e.g., Down syndrome, rheumatoid arthritis) or unstable cervical spine (e.g., trauma patient presenting with a cervical collar in situ). Sniffing position should be avoided in this patient population, with strong consideration for flexible scope intubation or video laryngoscopy to facilitate indirect laryngoscopy. However, if hypoxemia ensues on induction airway triumphs cervical spine and sniffing position is acceptable in dire situations.

Question 15

How is direct laryngoscopy performed?

Answer 15

Direct laryngoscopy can be performed using a variety of different blades. The two most common laryngoscope blades are the Macintosh (curved) and Miller (straight). Laryngoscope blades are available in various sizes that are chosen based on the patient’s size and anatomy but in general most patients can be intubated with a Macintosh 3 or Miller 2 blade.
Following induction of anesthesia, the mouth should be opened, as wide as possible, using the “scissor” technique to introduce the blade into the mouth. The laryngoscope should be held gripping the handle as low down as possible to provide maximal control. After the blade is advanced into the mouth, the provider should place their right hand under the patient’s head to extend the head and, if necessary, lift the head off the table (which flexes the neck) to facilitate sniffing position. The right hand can be used to align the airway axes so the glottic opening can be directly visualized, thus allowing the provider to use less force with their left hand holding the laryngoscope blade. Note, sniffing can also be realized using pillows or blankets to flex the neck before induction; however, sometimes this leads to excessive or inadequate neck flexion.
When using the Macintosh blade, the laryngoscope is advanced slowly into the mouth and down the tongue, while identifying relevant anatomy. Once the tip of the blade is in the vallecula (groove between the base of tongue and epiglottis), the provider lifts the blade upward and to the back corner of the room at a 45-degree angle.
This transmits a force to the hyoepiglottic ligament (see Fig. 3.1), which lifts the epiglottis off the posterior pharynx revealing the glottic opening. During laryngoscopy with the Miller blade, the tip of the blade is placed
just posterior to the epiglottis. The epiglottis is then lifted to reveal the glottic opening (Fig. 3.4). External manipulation of the larynx may be helpful to improve visualization with both blades. Glottic structures will be revealed in this order: (1) posterior arytenoids, (2) glottic opening, and (3) vocal cords.

Question 16

What is the classification system used to describe the view on laryngoscopy?

Answer 16

The quality of the view of the glottic structures is described by the Cormack-Lehane classification system: 1: Full view of glottis

2a: Partial view of glottis
2b: Only posterior glottis or posterior arytenoids seen
3: Only epiglottis seen (none of glottis)
4: Neither glottis nor epiglottis seen

Question 17

When is it appropriate to choose direct laryngoscopy(MacintoshorMillerblade) versus indirect laryngoscopy (video laryngoscope or flexible intubating scope)?

Answer 17

It is generally appropriate to proceed with direct laryngoscopy following induction of anesthesia in patients who have no history, risk factors, or evidence on examination consistent with a difficult airway. In patients in whom it is impossible to achieve sniffing position because of limited cervical range of motion or a desire to maintain cervical spine stability, indirect laryngoscopy can aid in visualization of the glottic structures.
Indirect laryngoscopy is generally used to facilitate endotracheal intubation in patients with a challenging airway or in clinical situations where cervical spine movement should be minimized. The flexible intubating scope, also referred to as the fiberoptic bronchoscope, is considered the gold standard to manage difficult airways, particularly in patients with a history of head and neck surgery, cancer, and/or radiation. Benefits of flexible scope intubation include complete visualization of the airway during intubation, confirmation of tube placement in the trachea, limited need for manipulating the cervical spine, and less potential for airway and dental trauma.

Question 18

How is a flexible scope intubation performed?

Answer 18

There are several steps in performing a flexible scope (fiberoptic) intubation. As with any procedure, it is imperative that the anesthesia provider ensure that all necessary equipment is available and in working order, including the flexible scope itself and backup equipment. Flexible scope intubation is most commonly performed with
the patient supine (although it can be performed in almost any position). It can be achieved via both orotracheal and nasotracheal routes. An antisialagogue (i.e., glycopyrrolate) may be given preemptively to minimize secretions that may obstruct the lens of the scope. The flexible scope is advanced into the oropharynx (or nasopharynx) and slight anterior deflection can bring the vocal cords into view. The scope is then advanced between the cords and into the trachea where the tracheal rings can be identified anteriorly. The scope is further advanced so the carina can be identified, at which point the endotracheal tube is advanced off the scope into the airway. After the endotracheal tube is placed in the trachea, the scope is withdrawn with care to ensure that the tube remains in place.

Question 19

What are indications for an awake intubation?

Answer 19

Flexible scope intubation can be performed with the patient “awake” or “asleep”. If the clinician has a suspicion that a patient may be difficult to mask ventilate and intubate, the patient is strong candidate for an awake intubation. A key factor in determining if a patient needs an “awake” versus an “asleep” intubation is if the patient is likely easy to mask ventilate. All the factors of difficult mask ventilation and intubation (listed in previous questions) should be considered. An awake intubation preserves oropharyngeal muscle tone, airway reflexes, and the ability to ventilate spontaneously. It does not require cervical spine manipulation. In addition, it may permit the clinician to minimize hemodynamic changes during induction as minimal induction medications are needed, once the endotracheal tube is properly placed.

Question 20

How is an awake intubation performed?

Answer 20

Flexible scope intubation in awake patients is well tolerated provided the airway is properly tropicalized with local anesthetic. Lidocaine is the first-choice local anesthetic in airway topicalization and has a long safety record with a high degree of success.
Reviewing the concepts behind airway topicalization for an awake intubation is a great way to review airway anatomy and its innervation. The glossopharyngeal nerve provides sensory innervation to the posterior one-third of the tongue, tonsils, soft palate, and pharynx up to the level of the epiglottis. To block this nerve, local anesthetic may be aerosolized into the oropharynx or applied via cotton swabs. Branches of the vagus nerve (superior laryngeal and recurrent laryngeal) provide sensory innervation to the airway below the epiglottis. The superior laryngeal nerve provides sensory innervation between the epiglottis and larynx. The superior laryngeal nerve block can be achieved by injecting local anesthetic lateral to the superior cornu of the hyoid bone bilaterally. The recurrent laryngeal nerve provides sensory innervation below the vocal cords. Block of this nerve is accomplished via transtracheal injection of local anesthetic. To achieve this, the cricothyroid membrane is identified, and a needle is advanced, until air is aspirated into the syringe attached to the needle, at which point local anesthetic is injected. Coughing induced by this block spreads the local anesthetic throughout the airway.

Question 21

Is it ok to give sedation to facilitate an “awake” intubation?

Answer 21

Airway topicalization and blocks are sometimes combined with sedation; however, it cannot be emphasized enough that the whole point of an “awake” intubation is that the patient needs to remain “awake” because of concerns of managing a difficult airway if the patient were to be sedated. Knowing the airway anatomy, its innervation,
and clinical competence in performing airway topicalization, related blocks, and using the flexible scope will reduce the need to sedate a patient to perform an “awake” intubation.

Question 22

We have talked about endotracheal intubation, but what other methods can be used for airway management?

Answer 22

Supraglottic airways (e.g., laryngeal mask airway) are devices that are inserted into the pharynx above the glottis to facilitate ventilation. They are less invasive than an endotracheal tube and more secure than a facemask. They are versatile and can be used for both spontaneous (negative pressure) and mechanical (positive pressure) ventilation. They do not require the use of neuromuscular blockade for placement, which is another advantage. Disadvantages include the lack of protection from laryngospasm or aspiration of gastric contents. They are generally used in healthy patients undergoing short operations (i.e., 1–2 hours), but can also
be used as a rescue device in patients who are difficult to intubate or as a conduit to facilitate flexible
scope intubation.

Question 23

What criteria do you use to determine if a patient is safe for extubation at the end of surgery?

Answer 23

Developing a plan for extubation is as important, if not more so, than a plan for intubation. In general, the criteria for extubation are the converse for the criteria to intubate. A patient is considered safe to extubate if: (1) they are awake and can protect their airway, (2) are not in hypoxemic respiratory failure, (3) are not in hypercapnic respiratory failure (this includes residual paralysis, overdose of opioids, or airway edema), and (4) are hemodynamically stable. In general, this can be realized by ensuring the patient is awake and alert with stable vital signs, can follow commands, has an adequate tidal volume and a normal respiratory rate (i.e., rapid shallow breathing index criteria <105), and can protect his or her own airway (exhibiting airway reflexes, such as gagging on the endotracheal tube). In addition, it is important to ensure adequate reversal of neuromuscular blockade via quantitative twitch monitoring as residual paralysis following extubation can lead to hypercapnic respiratory failure and failure to protect their airway.
Preparation for extubation should include placement of an oropharyngeal airway, preoxygenation with a fraction of inspired oxygen of 100%, and suctioning of the oropharynx. In patients at high risk for aspiration, precautionary steps may include decompression of the stomach with an orogastric tube and placement of the patient in the head up position.

Question 24

Why is it important to place an oropharyngeal airway in the patient’s mouth before emergence and extubation?

Answer 24

Oropharyngeal airways serve three important purposes on extubation. -First, the device displaces the tongue off the posterior oropharynx and palate, thereby preventing obstruction of the upper airway and impedance of gas flow during respiration. This is because patients emerging from anesthesia may not have adequate airway tone because of residual anesthetic or residual paralysis and therefore may be prone to upper airway obstruction, particularly in patients with a history of obstructive sleep apnea.

• Second, should respiratory support become necessary after extubation, a properly placed oral airway can serve as a conduit to maintain airway patency facilitating mask ventilation.
• Finally, the oral airway can be used as a bite block to prevent the development of negative pressure pulmonary edema, which can occur if the patient were to bite down on the endotracheal tube and attempt to inspire a large tidal volume.

Question 25

Which patients are at risk for “can’t intubate, can’t ventilate”? How does one manage this situation?

Answer 25

A CICV situation is also referred to as can’t intubate, can’t oxygenate (CICO) to emphasize that hypoxemia and not hypercapnia is the main problem because hypoxemia is the most frequent cause of death or complications in these situations. Furthermore, oxygenation does not necessarily require ventilation and other modalities, such as apneic oxygenation with high-flow nasal cannula, can be used to prevent this dreaded situation. Although a CICV situation may occur de novo without any apparent risk factors, a frequent cause is iatrogenic from airway
trauma because of multiple laryngoscopy attempts. In these situations, a provider is often initially able to mask ventilate; however, multiple direct laryngoscopy attempts may cause significant airway trauma (bleeding and edema) and the ability to mask ventilate is lost. Other specific risk factors include head and neck cancer, especially in patients who have received head and neck radiation treatment and in patients presenting with severe head and neck trauma (e.g., self-inflected gunshot wound to head/face). Most of these situations can be avoided or successfully managed by taking the following steps:
1) Have a low threshold to perform an awake flexible scope intubation in patients with known risk factors on history or by examination (e.g., head and neck cancer and/or radiation treatment)
2) Minimize laryngoscopy attempts (<2–3 attempts) and use the provider’s right hand to help align the airway axes so the blade can be gently held with the left hand to minimize airway trauma
3) Give paralytics if awaking the patient from anesthesia is not an option
4) Call for help early (surgeons and other anesthesia providers)
5) Perform a surgical cricothyroidotomy early (needle cricothyroidotomy is less favorable and has been shown to
have a high failure rate). Remember, a patient should never die from a CICV with a virgin neck See Fig. 3.5 for Difficult Intubation Guidelines.