A Variety of Techniques Provide Acceptable Anesthesia for Awake Intubation of the Airway; Ultimately, the Most Important Factors Are Operator Experience and Adequate Time



A Variety of Techniques Provide Acceptable Anesthesia for Awake Intubation of the Airway; Ultimately, the Most Important Factors Are Operator Experience and Adequate Time


Chauncey T. Jones MD



Awake fiber-optic intubations are an integral component of known difficult airway management. Operator experience in managing these airways is the most important variable. However, preparation of the patient and the airway weigh heavily in achieving a successful awake intubation.

Preparation of the patient involves discussion of what to expect and how the patient can help the process go smoothly, and then mild sedation, as respiratory status permits. However, sedation should not be to the point of airway obstruction or disinhibition of the patient.

Preparation of the airway involves administering an antisialagogue (such as 0.2 to 0.4 mg glycopyrrolate) to block the secretory reflex and anesthetizing the entire route that the intubation will take, whether nasal or oral. This course can be divided into nasal and oral cavies; nasopharyngeal, oropharyngeal, and hypopharyngeal regions of the pharynx; or subglottic regions, which include the larynx and trachea. The innervation of these regions must be blocked for successful awake intubation.


INNERVATION

Nasal cavity innervation is derived from two branches of the trigeminal nerve (V), the ophthalmic (V1) and the maxillary (V2). The anterior ethmoid nerve (from V1) innervates the anterior aspects of the nasal cavity and septum. The posterior nasal cavity and septum are innervated primarily by the lateral posterior superior, lateral inferior posterior, and nasopalatine nerves of V2.

The sensory innervation of the oral cavity and muscles of mastication derive from the mandibular branch of the trigeminal nerve (V3). Muscles of the tongue are supplied primarily by the hypoglossal, CN XII. Its general sensory path is from the lingual nerve, a branch of V3, for the anterior two thirds, and by the glossopharyngeal nerve, CN IX, for the posterior one third. The hard and soft palate are innervated by the greater and lesser palatine nerves, respectively, which are branches from V2.

Sensory innervation of the entire pharynx and epiglottis is supplied primarily by the glossopharyngeal nerve, CN IX, and motor nerve supply is
from the vegas nerve, CN X. The superior laryngeal nerve, derived from the vegas nerve, CN X, supplies sensory to the larynx above the true vocal cords as well as to the cricothyroid muscle. The recurrent laryngeal nerve, also from the vegas, CN X, supplies all other muscles of the larynx and sensation at the level of vocal cords and below. Recurrent laryngeal nerve also supplies sensory and motor components to the trachea.

Several protective reflexes can be elicited with airway manipulation, including gag, glottic closure (laryngospasm), and cough. These reflexes can be blocked by either their afferent (sensory) and/or efferent (motor) components. Input for the gag reflex is the glossopharyngeal nerve, CN IX, and output is the vegas, CN X. Fibers for glottic closure reflex are superior laryngeal for afferent and both superior and recurrent laryngeal for efferent. Other reflexes that may also be encountered are bronchospasm reflex, secretory reflex, vomiting reflex, and cardiovascular reflex.


ANESTHETIZATION OF THE AIRWAY

Anesthetization of the airway for awake fiber-optic intubation can be achieved by a number of techniques and can be adjusted to the patient, the operator preference, and availability of supplies (Table 4.1). These often include a mixture of topicalization and nerve blocks. Topicalization methods include direct application of lidocaine or viscous lidocaine, aerosol spray, atomization, or nebulization (Table 4.2). Common nerve blocks include glossopharyngeal, superior laryngeal, and translaryngeal. Other blocks may be performed, such as maxillary and mandibular nerve blocks. However, these are more invasive with a lower risk/benefit ratio, and their relevant terminal nerves can easily be blocked topically.








TABLE 4.1 COMMONLY USED TOPICAL METHODS FOR AIRWAY BLOCKS



























METHOD


LOCAL ANESTHETIC


NOTES


Nasal topical


1. 4% cocaine


2. 2% to 4% lidocaine or viscous lidocaine with 1% phenylephrine


Cocaine and phenylephrine cause vasoconstriction and decrease chance of epistaxis


Aerosol spray


Benzocaine


Risk of methemoglobinemia if maximum dose exceeded


Atomizer


4% lidocaine


Usually takes longer to work than direct topicalization


Nebulizer


4% lidocaine


Usually takes longer to work than direct topicalization


Syringe


2% to 4% lidocaine


Can be injected through nasal trumpet or slowly deposited onto the posterior tongue and run inferiorly to reach the hypopharynx

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Jul 1, 2016 | Posted by in ANESTHESIA | Comments Off on A Variety of Techniques Provide Acceptable Anesthesia for Awake Intubation of the Airway; Ultimately, the Most Important Factors Are Operator Experience and Adequate Time
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