Local Anesthesia for the Technique of Endoscopic Intubation—The Awake Intubation of the Difficult Airway

What follows is a summary of the method of local anesthesia for awake intubation in the Manual of Emergency Airway Management 4th ed. (1)

However, there are two earlier posts on awake intubation on my blog that are also helpful. The first is “How to Do an Awake Intubation—Two Outstanding Videos”, posted March 23, 2012. (2) The second is “More Details on Awake Intubation”, posted March 26, 2012 and has additional details from the videos. (3) You should watch both of the videos. One is 8 minutes and the other is approximately 30 minutes.

At the first thought that awake intubation using the endoscope might be advisable, you should administer IV glycopyrrolate because it takes a long time to dry secretions. Some authors say ten minutes, others say it takes fifteen to twenty minutes. The usual adult dose of glycopyrrolate is 0.4 to 0.8 mg IV (0.01 mg per kg).

Lidocaine is the drug used for topical airway anesthesia and it takes 2 to 5 minutes for maximum effect. The available concentrations are 2% (20 mg per ml) and 4% (40 mg per ml). Because topical lidocaine is systemically absorbed, the authors recommend a maximum lidocaine dose of 4 mg per kg to avoid potential toxicity. Calculate the maximum dose before you start.

“Aerosolization of aqueous lidocaine is easy and effective. Gas flow directed nebulizers, as are used for inhalation therapy in asthma, are an effective first step to initiate broad (nasal, oral, and hypopharyngeal) local anesthesia during an emergency airway situation. Four milliliters of lidocaine can be administered over 10 minutes while additional agents and equipment are prepared.”

“Atomizers produce larger droplets than nebulizers, such that medication rains out in the region local to  administration. For topical anesthesia of the upper airway, atomizers are more rapid and effective than nebulizers.” Examples are the Devilbiss atomizer and the Mucosal Atomization Device.

Nasal Anesthesia

“Topical vasoconstriction improves nasal passage caliber and prevents epistaxis. . . . Phenylephrine (Neosynephrine) 0.5 % or oxymetazoline (Afrin) 0.05% solution is sprayed and sniffed into each nostril 2 to 3 minutes before application of local anesthesia.”

“Commonly used techniques for focused nasal anesthesia include:

–Nebulize a mixture of 4 ml of 4% lidocaine with l ml of 1% phenylephrine.
–Atomize agent directly into the nostril while asking the patient to sniff
–Inject viscous anesthetic gel (4 ml) into the nares with a small syringe while asking the patient to
sniff. The gel can be distributed throughout the nasal passage using a cottoon tip applicator or
through insertion of a nasopharyngeal airway.”

Oral Anesthesia

The patient should swish and gargle with a 4% acqueous lidocaine solution.

Then “ ‘Butter’ the tonegue base with lidocaine paste, ointment, or gel applied with a tongue depressor. Apply 5 ml of 5% lidocaine evenly to the base of the protruded tongue just as you would apply butter to a piece of toast. Maintain the mouth open and the tongue protruded for several minutes to allow the formula to melt down the base of the tongue. Manual control of [the] tongue with guaze while asking the patient to pant ‘like a dog’ is an easy maneuver.”

You can also spray the tongue and oral cavity with an atomizer.

Oro- and Hypopharyngeal Anesthesia
The butter technique detailed above will provide effective anesthesia.

Laryngeal Anesthesia

You can provide local anesthesia with an atomizer or nebulizer of acqeous lidocaine. And as below you can inject lidocaine through the working channel of the endoscope while visualizing the structure.

Tracheal Anesthesia

In the past tracheal and laryngeal anesthesia was produced by needle puncture of the cricothyroid membrane and direct injection of the local anesthetic into the trachea, but this is not needed.

“The trachea is best anesthetized topically. Drying is unnecessary. Local anesthetic agent can be sprayed into the trachea through handheld spray devices, atomizer, or nebulizer. Additional anesthetic can be applied through the working channel during fiberoptic endoscopy.”

Awake Sedation Technique

In patients with upper airway obstruction, you should have the equipment and capability to proceed to surgical airway. This is because sedation and local anesthesia can lead to complete airway obstruction.

Low to moderate dose IV ketamine is an excellent agent for awake endospic intubation.

“Ketamine should be titrated in 10- to 20-mg aliquots IV until the patient can tolerate an awake look.”

If the cumulative dose of ketamine exceeds 1 mg per kg IV, the patient may experience cardiovascular or respiratory depression. Also if there is laryngeal inflammation, ketamine can lead to larygospasm.

There are other agents that may be appropriate for a given awake intubation and these are well discussed in the cited text.

The Uncooperative, Compative or Intoxicated Patient

“Uncooperative or intoxicated patients may require chemical restraint before and during airway assessment. If hypoxia or severe respiratory distress is the cause of the combative behavior, an awake technique is neither advised or likely to succeed. [Also, you will want to consider ruling out hypoglycemia as the cause, or empirically treating for it, if you can’t immediately rule it out.] Haloperidol, a butyrophenone, is rapid acting such that IV doses of 2 to 5 mg in the adult can be carefully titrated to effect at 3- to 5-minute intervals.

(1) Manual of Emergency Airway Management 4th ed, 2012. RM Walls and MF Murphy. Chapter 23, Anesthesia and Sedation for Awake Intubation, AC Heffner and PMC DeBlieux, pp.266-274. All quotes in this article are from this chapter.

(2) How to Do an Awake Intubation—Two Outstanding Videos, posted March 23, 2012 on my blog.

(3) More Details on Awake Intubation, posted March 26, 2012 on my blog.

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