Critical Care Medicine

Difficult airway management

Difficult Airway Management

Related conditions: Difficult mask airway, difficult intubation, respiratory compromise, cricothyrotomy, tracheostomy

Cannot intubate? Cannot Ventilate? What next!

1. Description of the problem

Difficulty in managing the airway is the single most important cause of major anesthesia-related morbidity and mortality. The most important factor in successful management of the difficult airway is recognition of the potential problem.

This requires meticulous evaluation as well as fastidious preparation of the patient. This could not be stressed more than in the ICU setting. In the ICU we are often confronted with urgent or emergent airways that need to be secured. During the ensuing rush to intubate the patient we do not stress that the patient is optimally positioned or even that we have the necessary equipment. To maximize our success and decrease acute event preparation is the key. When the patient is encountered, it is too late to check whether appropriate equipment is available, what the rescue plan is, or what alternative strategies there are for an immediate response.

There are few more terrifying situations than the patient who is in severe respiratory distress. Hypoxia induces fear not only in patients but also in all the providers at the bedside. During routine anesthesia the incidence of difficult tracheal intubation has been estimated at 3-18%. These numbers increase somewhat with increasing obesity and especially in the morbidly obese.

Difficulties in intubation have been associated with serious complications, particularly when failed intubation has occurred. If the provider can predict which patients are likely to prove difficult to intubate, the risks can be dramatically reduced. The most widely used classification is by Mallampati (Figure 1).

Figure 1.

Airway classification by Cormack and Lehane.

From the Cormack and Lehane classification (Figure 2) we can see 4 different views seen at the end of a laryngoscope. Grade l, we see the epiglottis arytenoids and vocal cords. Grade 2, we see the epiglottis and arytenoids. Grade 3, we see the tip of the epiglottis and posterior cartilages, and Grade 4, we see only the soft pharyngeal tissue with no identifiable airway anatomy.

Figure 2.

Mallampati Scoring System

Predicting Difficult Intubation

The classical positioning for intubation was described by Sir Ivan Magill as "sniffing the morning air". In this position the neck is flexed to about 35 degrees (usually by laying the head on a pillow). There is then extension at the atlanto-occipital junction. This theoretically aligns the structures in the upper airway and facilitates use of a curved laryngoscope blade. The problem with Magill's description is that there is wide variability in positioning and hence the angles are not consistent.

One can then follow general principles of medicine and perform a history followed by examination. The history we are seeking with a potential difficult intubation involves:

a. Previous difficult intubation

b. Unusual airway anatomy, such as those who have limited movement of their neck or jaw, or those who have tumors, deep swelling due to injury or allergy, developmental abnormalities of the jaw, or excess fatty tissue of the face and neck.

c. Type of surgery (if preop): for example, surgery involving the head and neck or bariatric surgery may lead one to anticipate difficulties with intubation.

d. Patients who have sustained trauma, burns or radiation injury will also prove troublesome!

When ascertaining the history, patients who are breathless or even stridulous may well find instrumentation of their airway intolerable.

These may suggest obstructing lesions in various locations within the upper airway, larynx or tracheobronchial tree.

A detailed physical examination of the airway is important, particularly:

Physical Exam: Predictors of difficult mask ventilation

1. Grade 3 Mask Ventilation - Difficult ventilation (inadequate, unstable, or requiring two providers) with or without muscle relaxant - 1.4% incidence

BMI > 30

Beard (the only easily modified risk factor)

Mallampati class III or IV

Age > 57 years

Limited jaw protrusion

Snoring

2. Grade 4 Mask Ventilation - Unable to mask ventilate with or without muscle relaxant - 0.16% incidence

Snoring

Thyromental distance < 6 cm

3. Grade 3 or 4 and difficult intubation (0.37%)

Limited mandibular protrusion

Abnormal neck anatomy

Sleep apnea

Snoring

BMI > 30

Physical Exam: Direct laryngoscopy (DL) difficulty: How to find it:

1. Focus on the three requirements for successful DL

a. Mouth must open (at least a little).

b. Three axes (tracheal, pharyngeal, oral) must be at least somewhat aligned in the sniffing (or sniff) position.

c. There must be a place big enough to put the tongue, and space to see.

2. Mouth opening; TMJ mobility. (Normal > 4 cm. Enough for blade may be enough for DL if no other problem.)

3. C-spine mobility; sniffing position:

a. Flexion of neck mainly, then a little

b. Extension of head (at atlanto-axial joint) on the flexed neck

4. Is there a place to put the tongue?

a. View patient's profile

i. Mandibular hypoplasia?

ii. Protruding incisors?

b. Palpation of neck, mandible, mandibular space (Mandible < 9 cm suggests difficult DL.)

c. Thyromental distance (Less than 6 cm suggests difficult DL.)

5. Upright maximal tongue protrusion test (Mallampati classification - see Figure 1)

Look for soft palate, uvula, tonsillar pillars:

Class I: tonsillar pillars and all of uvula

(only 0.4% were difficult)

Class II: more than base of uvula but not pillars

Class III: only base of uvula

Class IV: no uvula or soft palate

Yes, false positives and negatives do occur (up to 50%!)

6. Upper lip bite test:

3 classes:

Class 1, Lower incisors can hide mucosa of upper lip

Class 2, Lower incisors partially hide mucosa of upper lip

Class 3, Lower incisors unable to touch mucosa of upper lip

Class 3 would be interpreted as retrognathic (overbite) and adds significant difficulty to intubation.

2. Emergency Management

Emergency airway management often involves a combination of factors that increase the technical difficulty of intubation and increase patient risk. These factors include:

  • Dynamically deteriorating clinical situation, i.e., there is a real “need for speed”?

  • Non-cooperative patient

  • Respiratory and ventilatory compromise

  • Impaired oxygenation

  • Full stomach (increased risk of regurgitation, vomiting, aspiration)

  • Secretions, blood, vomitus, and distorted anatomy

Prior to intubation one must be prepared and have a full array of equipment that may be required, such as:

  • laryngoscopes with a selection of blades

  • a variety of endotracheal tubes

  • introducers for endotracheal tubes (stylets or flexible bougies)

  • oral and nasal airways

  • a cricothyroid puncture kit

  • reliable suction equipment

  • a trained assistant

  • laryngeal mask airways, sizes 3 & 4

Intubation rescue techniques may assist with either an anticipated or unanticipated difficult intubation. Intubation rescue is used following a failed intubation attempt, provided that

a. No more than several laryngoscopic attempts have been made,

b. Laryngoscopy has been attempted for <10 minutes, and

c. The patient's SpO2 can be maintained at >92%. If laryngoscopy has been attempted for >10 minutes or >3 times or the patient's SpO2 cannot be maintained at >92%, intubation attempts should be aborted and emergency ventilation using a Combitube, LMA, or other approved supraglottic airway device should be used until a definitive airway can be safely inserted using a different technique. If the clinical situation permits, the patient may be awakened and the surgical case postponed.

When a difficult airway is suspected, it is recommended to secure the airway with the patient awake, unless it is contraindicated. Various difficult-airway intubation techniques are currently available, and most can be performed with the patient awake while receiving a combination of intravenous sedation and topical local anesthesia of the airway.

Figure 3 shows airway outcome predictors.

Figure 3.

Airway outcome predictors

Rapid Sequence Intubation (RSI)

RSI refers to the pharmacologically induced sedation and neuromuscular paralysis prior to intubation of the trachea. The technique is a quicker form of the process normally used to induce general anesthesia. Medications are utilized to allow rapid placement of an endotracheal (ET) tube between the vocal cords, while the cords are being visualized with the aid of a laryngoscope. Once the ET has been passed between the vocal cords, a cuff is inflated around the tube in the trachea and the patient can then be ventilated manually.

RSI involves preoxygenating the lungs, followed by the sequential intravenous administration of predetermined doses of anesthetic drugs and a rapid-acting neuromuscular blocking agent. Commonly used hypnotics include propofol and etomidate. Unless there is a contraindication, succinylcholine is the most commonly used neuromuscular blocking agent given its rapidity of onset and short duration of action. Alternatively, rocuronium may be used at a dose of 1.2 mg/kg with similar speed of onset. Of note, the FDA recently approved Sugammadex, a selective binding agent for the reversal of moderate to deep rocuronium-induced neuromuscular blockade. Rapid reversal could prove useful in instances when tracheal intubation cannot be achieved. Atropine may be used to prevent a reflex bradycardia from vagal stimulation during laryngoscopy, especially in young children and infants. Despite their common use, such adjunctive medications have not been demonstrated to improve outcomes.

One important difference between RSI and routine tracheal intubation is that the practitioner does not manually assist the ventilation of the lungs after the onset of general anesthesia and cessation of breathing, until the trachea has been intubated and the cuff has been inflated. Another key feature of RSI is the application of manual pressure to the cricoid cartilage, often referred to as the "Sellick maneuver", prior to instrumentation of the airway and intubation of the trachea.

Preparing for RSI:

SOAP–ME: A mnemonic to prepare for intubation during rapid sequence intubation.

Suction: Yankauer suction catheter is within reach of the operator's hand during laryngoscopy. When properly connected, the suction is audible and palpable when the tip of the catheter is touched against the hand.

Oxygen: Bag valve mask resuscitator connected to an oxygen source at 15 L/min. The flow of oxygen should be audible and high enough to fill the reservoir bag or tubing. Squeeze bag against hand to verify positive pressure.

Airways: Oral and nasal airways and rescue ventilation devices, such as the LMA (#4, 5) and Small Adult Combitube. The cuff of the tracheal tube should be checked and fully deflated. The tracheal tube should be styletted with a straight-to-cuff shape. Tip of stylet should stop at or before distal edge of cuff, leaving the last 2-3 cm of tube flexible.

Positioning and Pre-Oxygenation: Ear-to-sternal notch positioning as described. Except in instances when laryngoscopy is done immediately (such as cardiac arrest and near arrest) pre-oxygenation with a well-fitting non-rebreather mask and high-flow oxygen (15 L/min) should be done for 4 minutes prior to RSI. Patients with inadequate spontaneous ventilation require bag mask ventilation as preparations for laryngoscopy are made.

Monitoring equipment and Medications: In patients without a pulse, laryngoscopy will occur immediately as monitoring is also being established. With RSI, the patient should have continuous pulse oximetry and cardiac monitoring, and pre- and post-procedure blood pressure monitoring. All medications should be drawn and labeled. The laryngoscopist should clearly communicate with all members of the care team regarding the sequence and timing of medications.

End-tidal CO2 device and Esophageal Intubation Detector: To verify tracheal placement after the tube has been placed, all patients require end-tidal CO2 monitoring, either by capnography, capnometry, or colorimetric testing. An esophageal intubation detector is useful for verifying tube location in cardiac arrest.

3. Diagnosis

Figure 4 shows an airway history and exam flowsheet. Figure 5 shows the ASA difficult airway algorithm. Figure 6 lists techniques for a difficult airway.

Figure 4.

Airway History and Exam Flowsheet

Figure 5.

ASA Difficult Airway Algortithm

Figure 6.

Techniques for a difficult airway

Difficult airway equipment:

  1. Bag Valve Mask

  2. Bougie

  3. LMA

  4. Fastrack (Intubating) LMA

  5. Lightwand

  6. Video Laryngoscope

  7. Bullard Laryngoscope

  8. Cricothyrotomy

  9. Transtracheal jet

  10. Retrograde

Videolaryngoscopy

Over the past two decades there has been a proliferation of videolaryngoscopes of various makes and designs in anesthesia and emergency airway practice. The videolaryngoscope is a device with a camera at the end of a laryngoscope blade with its image shown on a videoscreen. While the evidence is equivocal, several studies demonstrate improved Cormack and Lehane views with indirect laryngoscopy via videolaryngoscope versus traditional DL in a variety of settings, including the ICU.

In addition, studies show that intubation with certain videolaryngoscope models requires less cervical spine motion or provides better views with c-spine immobilization, making the scopes ideal for instances of suspected c-spine injury. Some proponents believe videolaryngoscopy should be the standard of care for all intubations citing the ability to capture video of the procedure in real time for inclusion in the patient’s chart, thus giving a record for future intubations.

Pathophysiology

Currently we have established that history and examination are key to diagnosis and management of a difficult airway. We have also seen that although difficult airways are unusual, anticipation and preparation are certainly life-saving measures. In an emergency there is often pressure to achieve airway access without all the correct equipment being present. Haste leads to poor history, examination and potential for a failed airway.

For those airways deemed very difficult, particularly if there is documentation of a previous difficult intubation we should achieve airway access through an awake fiber-optic intubation.

What's the Evidence?

Thompson, CA. "Sugammadex approved to reverse NMBA effect". Am J Health Syst Pharm. vol. 73. 2016 Feb 1. pp. 100.

Yang, L, Keam, S. "Sugammadex: A review of its use in anaesthetic practice". Drugs May. vol. 69. 2009. pp. 919-42.

Zaouter, C, Calderon, J, Hemmerling, T. "Videolaryngoscopy as a new standard of care". BJA. vol. 114. 2015. pp. 181-3.

Laosuwan, P, Earsakul, A, Numkarunarunote, N, Khamjaisai, J, Charuluxananan, S. "Randomized cinefluoroscopic comparison of cervical spine motion using McGrath Series 5 and Macintosh laryngoscope for intubation with manual in-line stabilization". J Med Assoc Thai. vol. 98. 2015. pp. S63-9.

Zamora, JE, Nolan, RL, Sharan, S, Day, AG. "Evaluation of the Bullard, GlideScope, Viewmax, and Macintosh using a cadaver model to simulate the difficult airway". vol. 23. 2011. pp. 27-34.

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