Local Anesthesia of the Airway Technique

Depending on the nerve supply and the region, the upper airway is divided into 3 regions (see image below).

Nasal cavity

The sensory supply is as follows:

• From the olfactory cranial nerve (CN 1): The anterior ethmoidal nerve supplies the nares and the anterior one third of the nasal septum.

• From the pterygopalatine ganglion via the maxillary division of the trigeminal nerve (CN 5): The greater palatine nerve and lesser palatine nerves. This ganglion lies posterior to the middle turbinate and the branches innervate the posterior two thirds of the nasal septum and the turbinates.

Base of tongue and oropharynx

The glossopharyngeal nerve travels anteriorly from the jugular foramen along the lateral aspect of the pharynx in close proximity to the structures in the carotid sheath and the styloid process and in the neck lies between the internal and external carotid arteries. Its branches provide sensation to the following structures:

• Lingual branch - Innervates the posterior one third of the tongue, vallecula, and anterior surface of epiglottis

• Pharyngeal branch - Innervates the lateral and posterior walls of the pharynx

• Tonsillar branch - Innervates the tonsillar pillars and soft palate

These branches lie immediately posterior to the palatine tonsils (see the images below).

Hypopharynx, larynx, and trachea

From the vagus nerve come the following nerves:

• Superior laryngeal nerve: This nerve is a branch of the vagus nerve. It courses medially in the neck and divides into the internal and external laryngeal branch lateral to the greater cornu of the hyoid bone and travels inferiorly to pierce the thyrohyoid membrane and travels under the pyriform fossa. The ascending branch supplies the epiglottis, aryepiglottic fold, and arytenoids. The descending branch supplies the laryngeal mucosa just above the vocal cords. The external laryngeal branch supplies the cricothyroid muscle.

• Recurrent laryngeal nerve: The recurrent laryngeal nerve arises from the vagus at the level of the ligamentum arteriosum and loops around the arch of aorta on the left side and under the right subclavian artery on the right side to ascend up into the tracheoesophageal groove. It provides sensory innervations below the vocal cords and trachea and motor supply to all the intrinsic laryngeal muscles except cricothyroid.

To summarize, for anesthetizing the nasal cavity, the maxillary branches from the trigeminal nerve must be blocked. Manipulations involve the pharynx and posterior third of the tongue require blocking of the glossopharyngeal nerve. Vagal nerve block is needed for structures beyond epiglottis.

Nasal cavity may be blocked either by the use of cotton pledgets or by an inhalational technique. The 2 techniques are described below.

By placing cotton pledgets soaked in local anesthetic solution

See the list below:

• Drugs: 4% lidocaine (lignocaine)

• Position: Patient lies supine with head end elevation by 30°

• Three wide cotton pledgets soaked in local anesthetic solution are applied along the 3 walls of the cavity.

• One pledget is placed along the inferior turbinate extending to the posterior pharyngeal wall.

• Second pledget is placed along the middle turbinate in a cephalad angulation to block the pterygopalatine ganglion under the sphenoid bone.

• A third pledget is placed along the superior turbinate close to the cribriform plate and posterior nasopharyngeal wall. This blocks the anterior ethmoidal nerves.

• The above procedure should be performed bilaterally to have a bilateral block.

• The pledgets are left in place for at least 5-15 minutes (see image below).

  Nasal packing is done with cotton pledgets

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Inhalation of aerosolized local anesthetic

4% lidocaine (lignocaine) can be added to a standard nebulizer or atomizer and kept on the patient’s face. The patient is asked to breathe in deeply for about 15-30 minutes.

Advantages of this technique are that it very simple and easy to perform, it is the least invasive, and, if performed properly, it can anesthetize the upper airway to the trachea. Knowledge of the anatomy of the airways is also not needed. It can be especially useful in patients in whom blocks are contraindicated or not feasible. The plasma levels of the local anesthetic are also not high.

The disadvantages of this technique are that the block may be uneven and less dense and may occasionally cause CNS depression. Additionally, the technique requires the patient to inhale deeply which may not be easy for all.

Anesthesia of the oral cavity and oropharynx can be achieved by topical techniques or by directly blocking the glossopharyngeal nerve.

Topical application

See the list below:

• Lidocaine (lignocaine) gel 2- 5% can be applied to the posterior third of the tongue.

• Lidocaine (lignocaine) spray 10% can be sprayed on the posterior third of the tongue and posterior pharyngeal wall after depressing the tongue with a tongue depressor.

• Cetacaine spray (a pressurized solution containing a mixture of 14% benzocaine and 2% tetracaine) can be used to spray the posterior third of the tongue and posterior pharyngeal wall.

• Viscous lignocaine 2% around 2-4 mL can be gargled for 30 seconds.

• Lidocaine (lignocaine 4%; 4mL) can be nebulized.

• Alternatively, a 10-mL syringe with 4% lidocaine (lignocaine) can be sprayed through a small bored needle

Caution: The toxic dose of the drugs should not be exceeded while using large quantities of the local anesthetics. ^[7]

Glossopharyngeal nerve block

Glossopharyngeal nerve can be blocked either by an intraoral technique or by a peristyloid technique.

Indication: A nerve block is attempted if the topical techniques are not effective in abolishing the gag reflexes.

Intraoral approach

• Position: patient lies supine

• The mouth of the patient is opened wide.

• The posterior pillar of the tonsillar fossa is identified after displacing the tongue to the opposite side with a tongue depressor.

• A 25-gauge spinal needle is inserted into the fold near the base of the tongue and advanced slightly.

• A syringe is attached and aspiration is done.

• If air is aspirated, the needle is advanced further.

• If blood is aspirated, the needle is redirected more medially.

• 2mL of 1% lignocaine is injected into the caudad portion of the posterior pillar./li>

Peristyloid approach

• Patient is positioned supine.

• A line is drawn between the angle of mandible and mastoid process.

• Styloid process is felt on this line just behind the angle of mandible.

• After preparing the skin with Betadine, a 22-gauge short bevelled needle is inserted at this spot and advanced medially.

• Once the bone is contacted, the needle is withdrawn slightly and directed slightly posterior.

• After negative aspiration, 5-7 mL of 1% lignocaine is administered.

This can be performed by either mucosal saturation of local anesthetic by the inhalational method or by performing nerve blocks. Complete anesthesia requires blockade of the superior laryngeal nerve as well as the recurrent laryngeal nerve. Remember, however, that complete anesthesia, especially of the recurrent laryngeal nerve, poses the danger of a blocked airway.

Superior Laryngeal Nerve Block

This nerve can be blocked directly or by topicalization.

Nerve block

• Patient position is supine with neck extended.

• The skin on the neck is prepared with an antimicrobial agent.

• The greater cornu of the hyoid bone is palpated. This is identified just below the angle of the mandible and by tracing upwards from the posterolateral surface of the thyroid cartilage.

• The hyoid bone is held between the index and thumb fingers of the operator and firm pressure is applied to displace it toward the side to be blocked.

• A 25-gauge needle is inserted to contact the greater cornu of the hyoid. The needle is then walked below this bone.

• The needle is advanced by 2-3 mm to enter the thyrohyoid membrane. In this position, the needle lies just outside the laryngeal mucosa (see image below). After negative aspiration for air and blood, 2 -3 mL of 1% lignocaine is injected. Presence of air indicates entry into larynx, and the needle should be withdrawn slightly. Presence of blood indicates entry into superior laryngeal vessels.

• The block has to be performed bilaterally.

  Superior laryngeal nerve block. The hyoid bone is held by the thumb and index fingers of the operator and displaced towards the side to be blocked

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Topicalization

This is performed only when the external approach (described above) is not feasible or has failed.

• Inhalation of aerosolized local anesthetic (as described above)

• Local application: After topicalization of the tongue, patient is asked to protrude the tongue, which is grasped with a piece of gauze. Pledgets soaked in 4% lignocaine are inserted bilaterally using a pair of right angled forceps into the pyriform fossa and left there for 5-15 minutes.

Recurrent Laryngeal Nerve Block

The 2 methods for this block include the following inhalational of aerosolized local anesthetic (as described above) and the transtracheal block (see the image below).

See the list below:

• Position: The patient is placed supine with neck extended.

• In the mid line, the thyroid prominence and the cricoid cartilage below it are identified.

• The cricothyroid membrane can be felt in the mid line between these 2 structures.

• After sterile preparation of the skin overlying the membrane and skin infiltration with local anesthetic, a 22-gauge intravenous cannula with needle is inserted through the membrane until resistance is lost and the needle has entered the larynx.

• The needle is removed, the cannula left in place, and a 5-mL syringe with 4 mL of 1 % lignocaine is attached.

• Aspiration is done, and, when air is aspirated, the local anesthetic is injected.

• During injection, the patient might cough. Care should be taken to avoid mucosal injury during this time.

Since the recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx, except the cricothyroid, direct blockade, especially bilaterally is contraindicated. This could lead to complete obstruction of the airway.