Local Anesthesia of the Airway

Procedures on the upper airway in an awake patient are challenging because of local factors such as excessive salivation, presence of gag reflex, and activation of cough reflex, as well as because of the systemic hemodynamic response caused by the stimulation of autonomic nervous system.

Anesthesia of the airway is needed for attempts to access a difficult airway or for procedures performed through the airway in awake patients. In patients with recognized difficult airway, intubation under general anesthesia might lead to the risk of loss of control on the airway. Elective awake intubation is a safer option in these patients and is facilitated by abolishing airway reflexes by local anesthetic techniques. Local anesthesia of the airway is complicated due to the multiple nerves that are to be blocked. A thorough knowledge of the anatomy is essential for a successful procedure.

These blocks are mainly performed to abolish reflexes and provide patient comfort during manipulation and instrumentation of the airways in an awake patient during the following:

• Direct laryngoscopy

• Bronchoscopy

• Nasal intubation

• Fiber optic intubation[1, 2]

• Some procedures on the head and neck

Most of these procedures are frequently done in patients with compromised airway before establishing endotracheal intubation for the induction and maintenance of anesthesia.

Absolute contraindications

Patient refusal is an absolute contraindication.

Relative contraindications

A patient on anticoagulation is a relative contraindication, as is distorted anatomy that interferes with the proper identification of structures to perform the block due to the following:

• Tumors

• Surgical deformities or reconstruction

• Arteriovenous malformations

If the structures are identified properly and knowledge of the anatomy is good, these blocks can be performed easily and with a high rate of success with the least amount of complications.

Elements of Informed Consent

Preparing a patient for awake airway instrumentation and manipulation requires proper planning. The patient is explained the procedure in adequate detail and should know what to expect. He should be aware of the reasons for performing the procedure awake. The patient is informed that he or she will be awake while the endotracheal tube or bronchoscope is inserted into his or her mouth or nose. He needs to be reassured that the discomfort can be largely mitigated by placing needles or inserting cotton into his nostril or any other local anesthetic technique that is suitable for performing the procedure on the airway. This is mostly a safe technique with not many complications. Temporary hoarseness or weakness of voice or coughing might occur in the postprocedure period.

See the list below:

• Antimicrobial solution for skin preparation (Betadine or chlorhexidine.)

• Short bevelled needles of 22-gauge to 25-gauge sizes

• 2 mL and 5 mL syringes

• Nebulizer or atomizer

• Tongue depressor

• Right-angled forceps

• Oxygen source and face mask

• Suction catheter and apparatus

• Monitors

• Routine monitoring devices like pulse oximeter, noninvasive blood pressure measurement, and ECG

Alleviation of anxiety

Sedation can be given after assessing the level of anxiety of the patient. Agents with a short duration of action that are titratable and reversible are preferred. They should also not depress the spontaneous respiration of the patient. Recommended titration is to the patient developing drowsiness or slurred speech.[3, 4, 5]

• Midazolam: 0.5-3 mg

• Fentanyl : 20-100 micrograms

• Alfentanil : 100-1000 micrograms

• Dexmedetomidine: 0.2-0.4 micrograms/kg/h

Oral secretions can interfere with visualization and performance of the airway procedure. Hence it should be decreased by administering antisialagogues intravenously or intramuscularly at least half an hour before the procedure, such as the following:

• Atropine: 0.5-1 mg

• Glycopyrrolate: 0.2-0.4mg

To reduce the risk of aspiration, keep the patient nil by mouth for at least 6 hours. Ranitidine and metoclopramide can be given 2 hours before the procedure.

If a procedure on the nose is planned, administering vasoconstrictor drops in the nostrils can help reduce the epistaxis due to trauma. Cocaine was used earlier as it is a good vasoconstrictor and local anesthetic. Currently, however, owing to concerns with substance abuse, it is not in use.

The following are administered half an hour before surgery and given after ruling out drug contraindications (ex, uncontrolled hypertension).

• 1% phenyl ephedrine spray

• Ephedrine drops

The patient is brought to the operating theater or any other place predetermined to perform the block with all facilities to provide the block safely and to manage any adverse events.

An intravenous cannula is started and all other monitors are connected to the patient.

Anesthesia

Various preparations of local anesthetics include the following:

• 1%, 2% , 4%,10% lidocaine (lignocaine) solutions

• 10% lidocaine (lignocaine) spray

• Lidocaine (lignocaine) 2-4% jelly

• Viscous lidocaine (lignocaine) 2%[6]

• Cetacaine spray (a pressurized solution containing a mixture of 14% benzocaine and 2% tetracaine

Complications

General

Because multiple nerve blocks have to be performed to abolish all airway reflexes, large volumes of local anesthetic might be needed. This could lead to the dose exceeding the toxic limits. Calculating the total dose that is allowed for the individual patient and drawing up only that amount and keeping it in a cup so that only contents of this cup will be put to use is a good practice.

The protective reflexes of the airway are lost. Therefore, chances of aspiration are high. This can be reduced by keeping the patient nil by mouth for a period of 6 hours and prescribing antiaspiration prophylaxis.

Mucosal trauma epistaxis is a complication involving the nasal cavity.

Glossopharyngeal nerve block

• Intraoral approach: Intravascular injection and hematoma formation due to close proximity to internal carotid artery.

• Peristyloid approach: Intravascular injection into the internal jugular vein and external carotid artery and hematoma formation.

Superior laryngeal nerve block

This block might rarely injure and cause intravascular injection into the superior laryngeal artery or vein as they lie in proximity to the nerve on the thyrohyoid membrane.

Loss of protective airway reflexes can cause complications like aspiration.

Transtracheal block

The patient might cough during injection of the drug. Trauma to the laryngeal mucosa can occur. Using the intravenous cannula and rapid injection of the drug once the airway is entered can minimize this risk.

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

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

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.

The aims of premedication are to reduce morbidity, prevent complications, and minimize myocardial oxygen demands by reducing heart rate and systemic arterial pressure.

Class Summary

Administration of intravenous midazolam in the operating room can reduce anxiety, tachycardia, and hypertension.

Midazolam

Midazolam is a short-acting benzodiazepine with a rapid onset of action. It depresses all levels of the CNS (eg, limbic and reticular formation), possibly by increasing activity of GABA.

Class Summary

Induction of anesthesia is accomplished by using high doses of opioid (usually fentanyl or alfentanil) to maximize cardiovascular stability.

Fentanyl citrate (Duragesic, Abstral, Actiq, Fentora, Onsolis)

Fentanyl citrate is a synthetic opioid that has 75-200 times more potency and a much shorter half-life than morphine sulfate. It has fewer hypotensive effects than morphine and is safer in patients with hyperactive airway disease because of minimal or no associated histamine release. By itself, fentanyl citrate causes little cardiovascular compromise, although the addition of benzodiazepines or other sedatives may result in decreased cardiac output and blood pressure.

Fentanyl citrate is highly lipophilic and protein-bound. Prolonged exposure to it leads to accumulation of the drug in fat and delays the weaning process. Consider continuous infusion because of the medication's short half-life.

Alfentanil (Alfenta)

Ultra short acting analgesic that inhibits ascending pain pathways, increases pain threshold, and alters pain perception.

Class Summary

Anticholinergic agents can inhibit salivation and excessive secretions of the respiratory tract before surgery. These agents also control upper airway secretions.

Glycopyrrolate (Robinul, Cuvposa)

Glycopyrrolate acts in smooth muscle, the central nervous system (CNS), and secretory glands, where it blocks the action of ACh at parasympathetic sites.

Atropine (AtroPen)

Atropine is an antimuscarinic agent that inhibits the action of acetylcholine at parasympathetic sites in smooth muscle, the CNS and secretory glands.

Class Summary

Prokinetics are promotility agents, proposed for use with severe constipation-predominant symptoms.

Metoclopramide (Reglan, Metozolv)

Metoclopramide is characterized by remarkable stimulation of gastric emptying without stimulating gastric, pancreatic, or biliary secretions. Increases lower esophageal sphincter tone. Metoclopramide can be given two hours before the procedure.

Class Summary

H2 blockers are reversible competitive blockers of histamine at H2 receptors, particularly those in the gastric parietal cells (where they inhibit acid secretion). The H2 antagonists are highly selective, they do not affect the H1 receptors, and they are not anticholinergic agents.

Histamine 2 (H2)–receptor antagonists should be administered preoperatively to prevent increase in gastric secretion during the procedure.

Ranitidine (Zantac)

This agent inhibits histamine stimulation of H2 receptors in gastric parietal cells, which reduces gastric acid secretion, gastric volume, and hydrogen ion concentrations. Histamine 2 (H2)–receptor antagonists should be administered preoperatively to prevent increase in gastric secretion during the procedure.

Famotidine (Pepcid)

Famotidine competitively inhibits histamine at the H2 receptors in gastric parietal cells, reducing gastric acid secretion, gastric volume, and hydrogen concentrations. Histamine 2 (H2)–receptor antagonists should be administered preoperatively to prevent increase in gastric secretion during the procedure.

Nizatidine (Axid, Axid AR)

This agent competitively inhibits histamine at the H2 receptor of the gastric parietal cells, resulting in reduced gastric acid secretion, gastric volume, and reduced hydrogen concentrations. Histamine 2 (H2)–receptor antagonists should be administered preoperatively to prevent increase in gastric secretion during the procedure.

Cimetidine (Tagamet HB 200)

This agent inhibits histamine at H2 receptors of gastric parietal cells, which results in reduced gastric acid secretion, gastric volume, and hydrogen concentrations. Histamine 2 (H2)–receptor antagonists should be administered preoperatively to prevent increase in gastric secretion during the procedure.

Class Summary

These agents may be used to treat nasal congestion.

Ephedrine

Ephedrine releases tissue stores of norepinephrine, which when applied nasally produces local vasoconstriction resulting in nasal decongestion.

Class Summary

Local anesthetics are used for local pain relief.

Lidocaine (Xylocaine with epinephrine)

Lidocaine 1-2% with or without epinephrine (1:100,000 or 1:200,000 concentration) is used. Lidocaine is an amide local anesthetic used in 1-2% concentration. The 1% preparation contains 10 mg of lidocaine for each 1 mL of solution; the 2% preparation contains 20 mg of lidocaine for each 1 mL of solution. Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels. Epinephrine prolongs the duration of the anesthetic effects from lidocaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

Benzocaine, butamben, and tetracaine (Cetacaine)

These agents inhibit the conduction of nerve impulses by decreasing the neuronal membrane's permeability to sodium ions.