Topical Anesthetics and Anesthesia for Awake Intubation



Topical Anesthetics and Anesthesia for Awake Intubation


Jarrod M. Mosier



INTRODUCTION

“Awake” intubation is often incorrectly described as any intubation where a neuromuscular blocking agent is not used, or where the patient is sedated but not yet apneic. The hallmark of an awake intubation is a conscious and cooperative patient for the purpose of maintaining safety and spontaneous breathing for predicted anatomic difficulty preventing rigid oral laryngoscopy or mask ventilation, or for refractory physiology intolerant of apnea or induction. With this being the context, the most critical component of an awake intubation is not how you view the airway, but topicalization of the airway to facilitate manipulation in an awake patient.

There are several indications where topicalization of the airway for an awake intubation is indicated:



  • Patients with predicted difficulty with laryngoscopy and mask ventilation (either with a bag-valve mask or an extraglottic device) where laryngoscopy with hyperangulated video laryngoscopy is not likely to be successful.


  • In some patients in the phenotype above, an “awake look” may be useful where the airway is topicalized and a laryngoscope is inserted. If the airway has a favorable view, the patient then undergoes full induction with a sedative and paralytic. Topicalization is required for the awake look.


  • All patients undergoing a flexible endoscopic intubation for any reason.


  • Patients with refractory physiology where a safe apnea time is not possible, or hemodynamics are too fragile for induction.


  • Endoscopic airway evaluation (e.g., hoarseness, stridor, hemoptysis, suspected foreign body or mass, inhalation injury, or neck trauma).

The only contraindication to an awake strategy is the need for immediate intervention for a rapidly deteriorating airway where time is insufficient to permit preparation (see Chapter 9, Developing your strategy). A critical element of topicalization is managing secretions or blood that may limit the effectiveness of topicalization.

This chapter will focus solely on the topicalization with or without sedation in patients where an awake intubation is performed. The procedural aspects of an awake intubation are described in detail in Chapter 25, Flexible Endoscopic Intubation and Chapter 28, Combination Techniques. image Video 16.1, demonstrates topicalization and accompanies this chapter.



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Video 16.1. Topicalization


TOPICALIZATION OF THE OROPHARYNX, HYPOPHARYNX, AND GLOTTIC STRUCTURES

Local anesthesia of the airway may be achieved topically, by injection, or both techniques and there are many proposed methods of topicalizing the airway to block the glossopharyngeal nerve. The following is the way we routinely tropicalize with minimal airway manipulation (as opposed to using Jackson forceps) and has been highly effective.



Step 1: Dry the mucous membranes

Airway secretions both dilute topical anesthetics and limit the contact with the mucous membranes. If time permits, antisialagogues can attenuate this effect. However, this requires some time and is not critical, so may not be feasible in all patients. The antimuscarinic agent glycopyrrolate is the preferred agent (0.005 mg/kg; usual adult dose 0.2 to 0.4 mg IV). The greatest drawback to its use is time to effective drying, which is 10 to 20 minutes following IV administration.


Step 2: First pass of atomized lidocaine

Lidocaine is an ideal agent because of its rapid onset (2 to 5 minutes to peak effect), useful duration (15 to 90 minutes), safety profile, and widespread availability. Concentrations of 4% (40 mg/mL) aqueous solutions are commonly available in the endoscopy suite for bronchoscopies and are the optimal concentration for topicalization. Two percent aqueous solution is widely available and useful for instillation through an endoscope but is not the preferred concentration for atomization. The addition of epinephrine provides no advantage.

The lidocaine should be atomized, not nebulized. Nebulizers are designed to create small particle sizes for distribution into the distal airways (e.g., bronchodilators). Nebulized lidocaine will not contribute in any meaningful way to topicalization of the upper airway. Further, lidocaine is well absorbed from the trachea and distal airways, and a large but variable fraction is exhaled. This unpredictably increases the risk of systemic toxicity and complicates estimates of the total lidocaine used. Atomizers, however, are designed to produce large droplets that deposit on the airway mucosa, providing more rapid, effective, and targeted block. Commonly available, effective devices for local anesthetic atomization are shown in Figure 16.1.