Of all the regional anesthesia techniques, airway blocks are the most critical and should be mastered by all anesthesia providers. These techniques are employed frequently with the diagnosis of a difficult airway, with trauma, and in emergent situations. They are usually performed on sedated, spontaneously ventilating "awake" patients requiring tracheal intubation (with need to maintain "awake" protective airway reflexes). Most situations call for a combination of these techniques as described below.
Preparation:It is recommended, that before proceeding with any of these techniques:
1. The adult patient is prepared by giving an explanation of the need for awake intubation, nasal endoscopy or other airway procedure, and will be more cooperative once they understand the rationale for any uncomfortable procedures that must be performed.
2. Preparation of the patient includes the use of antisialogogues (atropine 0.5-1 mg or glycopyrrolate 0.2 -0.4 mg IV) and the use of a vasoconstrictor for the nasal mucosa (1% phenylephrine spray) in the absence of contraindications to either. To be most effective, they should be administered 30-45 minutes prior to application of the local anesthetic (often in the holding area) to decrease the amount of secretions (essential to the use of indirect optical instruments such as the fiberoptic bronchoscope and rigid fiberoptic laryngoscope). They decrease saliva production, increase the effectiveness of topically applied local anesthetics by removing the barrier to mucosal contact, decrease drug dilution and are important to the success of these techniques.
General Indications for Airway Blocks:
To provide airway blocks before anesthetic induction in patients with airway compromise, trauma to the upper airway, or cervical instability.
To abolish or blunt reflexes such as laryngospasm, coughing, and other undesirable cardiovascular reflexes that often occur during procedures that involve manipulation of the airway (awake laryngoscopy, nasal intubation, and fiberoptic intubation).
To provide patient comfort and airway anesthesia during the performance of these procedures.
The following blocks are discussed:
Anesthesia of the Nasal Mucosa and Nasopharynx (Nasal Intubation)
Anesthesia of the Mouth, Oropharynx and Base of Tongue
Anesthesia of the Hypopharynx, Larynx and Trachea
Figure 1 (below): The three principal neural pathways of the airways and their related anatomy.
(click on pictures to see larger images)
Related Anatomy of Airway Blocks:
Innervation of the airway can be separated into three principal neural pathways:
Nasal/Nasopharyngeal Cavity – Maxillary branches of the Trigeminal Nerve (CN V)
Indicated for Nasal Intubations or Procedures
Oropharyngeal - Glossopharyngeal Nerve (CN IX)
Indicated for manipulations involving areas above the epiglottis,
Pharynx and Posterior 1/3 of Tongue, and Laryngoscopy
Laryngeal Cavity & Trachea - Branches of the Vagus Nerve (CN X)
Indicated for blocking of structures more distal in airway to the epiglottis
*There is no single nerve that can be blocked to produce complete anesthesia of the airway.
(Left): Ophthalmic (V1), and Maxillary (V2) Nerves.
[*Note the following structures: Trigeminal nerve (V), Maxillary nerve (V2), Pterygopalatinum (Sphenopalatine) ganglion, Nasal branch of the maxillary nerve, External nasal branch of the anterior ethmoidal nerve.]
I. Anesthesia of the Nasal Mucosa and Nasopharynx
Indications:To provide anesthesia for the passage of a nasotracheal tube To provide the initial steps for blunting of airway reflexes associated with awake nasotracheal, oropharyngeal and fiberoptic intubations.
Drugs:4% Lidocaine with epinephrine (or cocaine is a 4% solution – max. 200 mg in adult), or mixture of Lidocaine 3% and Phenylephrine 0.25% -
Anatomy:Sensation is via the middle division (V2) of the Trigeminal nerve (CN V), which lies below the nasal mucosa, posterior to the middle turbinate. Innervation to the nasal mucosa and nasal cavity involves the sphenopalatine ganglion (Meckel’s or pterygopalatinum ganglion) and the ethmoid nerve. Preganglionic fibers are derived from the facial nerve via the greater petrosal nerve and nerve of the pterygopalatinum canal. The postganglionic fibers supply the lacrimal, nasal and palatine glands. Sensory and sympathetic fibers pass through the ganglion).
Patient Position: Patient is most comfortable when head of bed is elevated approximately 30˚.
Technique: *Application of long cotton-tipped applicators or wide cotton pledgets soaked in the local solution (lidocaine and cocaine or phenylephrine) are applied over the nasal mucosa by inserting applicators into both nares in the following manner:
1. one applicator is placed along the inferior turbinate to the posterior nasopharyngeal wall
2. a second applicator is placed in a cephalad angulation along the middle turbinate, back to the mucosa covering the sphenoid bone (most important as it is the one most likely to anesthetize branches of the sphenopalatine ganglia as they pass along the lateral wall of the airway )
3. a third applicator may be placed along the superior turbinate, resting against the cribiform plate and posterior nasopharyngeal wall, providing anesthesia to the anterior ethmoid nerve
4. The applicators are then left in place for 5 minutes, and the pledgets for 2-3 minutes. (The use of wide cotton pledgets placed into the same areas with alligator forceps provides maximal topical anesthesia and vasoconstriction of the nasal mucosa).
Additionally, *nasal airways, in increasing sizes, can be lubricated with Lidocaine 2-5% jelly, and passed into the nostril being intubated for additional patient comfort.
*These procedures allow for blocking of the sphenopalatine (or Meckel’s ganglion) and the ethmoid nerve.
They should be done bilaterally provide posterior pharyngeal anesthesia, caudad to this level.
Assessment of Block Efficacy:Patient tolerates introduction of nasal airways and/or nasal intubation.
Complications: Epistaxis can occur due to trauma to nasal mucosa. Also, systemic toxicity can occur, thus doses of anesthetic delivered to the patient should be monitored to prevent exceeding the maximum dosages. Loss of protective laryngeal reflexes may place patient at increased risk for aspiration.
II. Anesthesia of the Mouth and Oropharynx
Indications:abolition of the gag reflex or hemodynamic response to laryngoscopy.
Drugs: Cetacaine spray (mix of 14% Benzocaine and 2% Tetracaine), Lidocaine spray 10%, Lidocaine gel 2-5%, Viscous lidocaine 2%, Tetracaine .5% soln, Lidocaine 4% soln.
Anatomy: Sensation of the oral mucosa and oropharynx are supplied by branches of the glossopharyngeal nerve (CN IX), vagus (CN X) and facial nerve (CN VII). The glossopharyngeal nerve travels anteriorly along the lateral surface of the pharynx, with it’s three branches supplying sensory innervation to the posterior third of the tongue, vallecula, anterior surface of the epiglottis (lingual branch), posterior and lateral walls of the pharynx (pharyngeal branch), and the tonsillar pillars (tonsillar branch). It also provides motor innervation to the stylopharyngeus muscle, involved in deglutition.
Patient Position: Supine
Lidocaine gel can be placed on tongue blade and patient "sucks" on this for several minutes. Lidocaine is available in a variety of concentrations and preparations. Topically, peak onset is usually within 15 minutes. Toxic plasma levels are possible to achieve, but not common with these techniques.
4cc of 4% Lidocaine or 0.5% Tetracaine can be placed in a nebulizer. The patient then inhales the nebulized local anesthetic for 5-7 min, or the tongue and posterior pharynx are sprayed with the atomizer.
Cetacaine spray (tetracaine and benzocaine combination) may also be used to provide anesthesia to the tongue and posterior pharynx. Keep in mind that the toxic dose of benzocaine is 100 mg (may cause methemoglobinemia, treated with the administration of methylene blue) and the toxic dose of Tetracaine is 100 mg in the adult (but toxicity has been reported at 40 mg). Check concentrations.
Viscous lidocaine 2-4 ml may also be used as a gargle (swish and swallow) for approx. 30 sec.
GLOSSOPHARYNGEAL NERVE BLOCK is performed when topical techniques are not completely effective in obliterating the gag reflex. This block can be performed after the mouth and oropharynx are adequately anesthetized. Branches of this nerve are most easily accessed as they transverse the palatoglossal folds (seen in figure 5, as soft tissue bilaterally). This is performed with the anesthetist standing contralateral to the side to be blocked and the patient’s mouth wide open. The palatopharyngeal fold (posterior tonsillar pillar) is identified and a tongue blade, held with the non-dominant hand, is introduced into the mouth to displace the tongue medially (contralateral side) creating a gutter between the tongue and the teeth. A 25g spinal needle is inserted into the membrane near the floor of the mouth at the base of the cul-de-sac (figure 4) and advanced slightly (0.25-0.5 cm). An aspiration test is performed. If air is aspirated, the needle has passed through the membrane (through and through). If blood is aspirated, the needle is redirected more medially. Then, 2 ml of 1% Lidocaine can be injected into the anterior tonsillar pillar 0.5 cm lateral to the base of the tongue (This most readily blocks the lingual branch). This block has been reported as painful, and may result in a persistent hematoma.
(Left)Palatoglossal arch (see arrow), is a soft tissue fold, continuing from posterior edge of the soft palate to the base of tongue.
A posterior approach (*often used for tonsillectomy), may be difficult, in visualizing the site for needle insertion, which is behind the palatopharyngeal arch (where the nerve is in close proximity to the carotid artery). There is risk for arterial injection and bleeding, and the technique is usually reserved for otolaryngologists. Steps for this procedure can be found in other sources and are not cited here.
Complications:Systemic toxicity - can occur quickly when several different techniques are used. Topical anesthetics enter the circulation more quickly than when injected into tissues, and can be absorbed in the respiratory and GI tracts. Local anesthetics should be carefully measured with a syringe or cup (when able) to monitor the dosages the patient is receiving. Concentrations should be considered when using sprays or other such preparations. The lowest concentration possible should be used to minimize the risk of toxicity. Methemoglobinemia – occurs when the ferrous molecule in hemoglobin is changed to its ferric state with essentially ionic bonds by oxidation. Injury or toxic agents convert abnormally large amounts of hemoglobin to methemoglobin, which does not function reversibly as an oxygen carrier. Results in cyanosis and many other symptoms which can progress to stupor, coma and death.
III.SUPERIOR LARYNGEAL NERVE (SLN) BLOCK
Indications:To block the internal (sensory) branch of the SLN, resulting in abolition of the gag reflex or hemodynamic responses to laryngoscopy or bronchoscopy.
Drugs: 2-4 ml of Lidocaine 1% or 2% lidocaine, with or without epinephrine.
Anatomy: At its origin from the vagus nerve (CN X), the SLN travels alongside with the vagus nerve deeply to the carotid artery, before becoming anterior. The internal branch of the superior laryngeal nerve originates from the SLN lateral to the cornu of the hyoid bone. It travels along inferior to the greater cornu, then pierces the thyrohyoid membrane, and travels under the mucosa in the pyriform recess. The internal branch of the SLN provides sensory innervation to the base of the tongue, superior epiglottis, aryeppiglottic folds, arytenoids and laryngeal mucosa (to just above and excluding the vocal cords). There are two branches: the ascending branch supplies the epiglottis and the vestibules of the larynx, whereas, the descending branch supplies innervation to the mucosa at the level of the vocal cords. *The external branch of the SLN supplies the motor innervation to the cricothyroid muscle.
(Left)Depicting the Vagus nerve branching into Superior Laryngeal and Recurrent Laryngeal nerve.
Note the insertion of Superior Laryngeal Nerve into ThyroHyoid Membrane.
Local Anesthetic: The internal branch is the nerve of interest in the superior laryngeal nerve block; it is blocked where it enters the thyrohyoid membrane just inferior to the caudal aspect of the hyoid bone. It provides anesthesia of the larynx from the epiglottis to the level of the vocal cords.
Patient Position: Supine, with head slightly extended.
Patient is asked to open the mouth widely, and the tongue is grasped using a guaze pad or tongue blade. A right angle forcep (e.g., Jackson-Krause) is covered with anesthetic-soaked guaze and is slid over the lateral tongue and down into the pyriform sinuses (recessus piriformis – pear-shaped fossa in the wall of the laryngeal pharynx, lateral to the arytenoids cartilage, and medial to the lamina of the thyroid cartilage) bilaterally. Cotton swabs are held in place for 5 minutes. (Less common procedure).
Anesthetist is positioned on the ipsilateral side of the neck. The cornu of the hyoid bone is palpated transversally with the thumb and the index finger on the side of the neck immediately beneath the angle of the mandible and anterior to the carotid artery. To facilitate its identification, the hyoid bone is displaced toward the side being blocked. One hand displaces the carotid artery laterally and posteriorly. With the other hand, a 22 or 23 guage - 25 mm needle is "walked off" the cornu (cartilage) of the hyoid bone in an anterior caudad direction, aiming in the direction of the thyroid ligament, until it can be passed through the ligament. At a depth of 1-2 cm, 2 ml of 2% lidocaine with epinephrine is injected (after negative air and blood aspiration) into the space between the thyrohyoid membrane and the pharyngeal mucosa. An additional 1 ml is injected as needle is withdrawn. The block is repeated on the other side.
Technique Tips! Firmly displace the hyoid bone towards the side to be blocked, even if it causes the patient some minor discomfort. Use small amounts of sedation to offset patient discomfort.
Exercise caution - not to insert the needle into the thyroid cartilage, since injection of local anesthetic at the level of vocal cords may cause edema and airway obstruction.
If air is aspirated, laryngeal mucosa has been pierced, and the needle needs to be retrieved.
If blood is aspirated (superior laryngeal artery or vein), the needle needs to be redirected more anteriorly. Pressure should be applied to avoid hematoma formation.
Assessment of Block Efficacy: Patient has an acceptable block and tolerates awake intubation.
Complications: Systemic toxicity - can occur quickly when several different techniques are used. Topical anesthetics enter the circulation more quickly than when injected into tissues, and can be absorbed in the respiratory and GI tracts. Local anesthetics should be carefully measured with a syringe or cup (when able) to monitor the dosages the patient is receiving. Concentrations should be considered when using sprays or other such preparations. The lowest concentration possible should be used to minimize the risk of toxicity.
Methemoglobinemia – occurs when the ferrous molecule in hemoglobin is changed to its ferric state with essentially ionic bonds by oxidation. Injury or toxic agents convert abnormally large amounts of hemoglobin to methemoglobin, which does not function reversibly as an oxygen carrier. Can result in cyanosis, and many other signs and symptoms, progressing to stupor, coma and death.
Hematoma formation - from puncture during needle placement for injection or vascular structure damage. Maintain pressure long enough to prevent hematoma or continued bleeding.
Tracheal anatomy depicting Superior Laryngeal Nerve with ascending and descending branches.
Superior Laryngeal Nerve Block – showing displacement technique.
Placement of Needle for the Superior Larnyngeal Nerve Block
IV. RECURRENT LARYNGEAL NERVE BLOCK – (TRANSTRACHEAL or TRANSLARYNGEAL BLOCK)
Indications:Transtracheal injection performed to block the recurrent laryngeal nerve for awake laryngoscopy, fiberoptic and/or retrograde intubation. Abolition of the gag reflex or hemodynamic responses to laryngoscopy or bronchoscopy. Used to help avoid Valsalva-like straining that may follow other "awake" intubations (patient is sedated and spontaneously ventilating).
Drugs: Most often, 3-4 ml of Lidocaine 4 % is used. Also, 1% or 2% lidocaine, with or without epinephrine. * Keep total dose of local anesthetics in mind when several of these techniques are performed!
Anatomy: Translaryngeal block is most useful in providing topical anesthesia to the laryngotracheal mucosa, innervated by branches of the vagus nerve – (CN X). The distal airway mucosa (like the upper airway from the SLN) receives innervation from the vagus nerve also, but via the recurrent laryngeal nerve (RLN). The right recurrent laryngeal nerve originates at the level of the right Subclavian artery, and loops around the inominate artery on the right, and around the aortic arch on the left. This nerve supplies sensory innervation to the vocal cords and trachea, and motor innervation to the vocal cords.
Translaryngeal injection of local anesthetic provides topical anesthesia for both vagal branches (SLN & RLN) since injection below the cords, through the cricothyroid membrane, and results in the solution being spread onto the tracheal (RLN) structures, and coughed onto the more (SLN) structures.
Patient Position: Supine, with neck hyperextended (or pillow removed and extended).
Technique: Inform the patient about the procedure, what is expected of him, and likelihood of coughing. Anesthetist should be in position to place index and third fingers of the non-dominant hand in the space between the thyroid and cricoid cartilages (identifying the cricothyroid membrane). The trachea can be held in place by placing the thumb and third finger on either side of the thyroid cartilage. The midline should then be identified and injected lightly to create a local skin wheal (using a 22-guage or smaller needle). A 10 ml syringe containing 4% lidocaine (or other desired concentration), is mounted on a 22-guage, 35 mm plastic catheter over a needle, and is introduced into the trachea. The catheter is advanced into the lumen, midline thru the cricothyroid membrane, at an angle of 45 degrees, in a caudal direction. *Immediately after the introduction of the catheter into the trachea, a loss of airway resistance and aspiration of air confirms placement, and the needle is removed from the catheter. The patient is then asked to take a deep breath and then asked to exhale forcefully. At the end of the expiratory effort, 3-4 ml of local anesthetic solution is rapidly injected into and over the back of the trachea. This will usually cause patient to first inhale to catch his or her breath and then forcefully cough, spreading the lidocaine over the trachea, making distal airway anesthesia more predictable This area is nearly devoid of major vascular structures.
Technique Tips! Caution! If a regular needle is used to inject (rather than a catheter), the lidocaine is injected rapidly and the needle is removed immediately!!! Surrounding structures, including the posterior tracheal wall can be damaged if the needle is not stabilized during injection of the local anesthetic and then be removed immediately!
The catheter should bet in place until the intubation is completed for the purpose of injecting more local anesthetic, if necessary, and to decrease the likelihood of subcutaneous emphysema.
Placement of fingers to identify the midline of the cricothyroid membrane.
Placement of the needle for the Transtracheal or Recurrent Laryngeal Nerve Block.
Transtracheal spread of local anesthetic with coughing.
Complications:Gastric Aspiration - This technique is possibly contraindicated in patients with high risk of gastric aspiration, but is believed by most authorities to actually decrease the risk, by decreasing risk of coughing and gag reflex during intubation.
Risk of Coughing – this block usually rapidly results in a fit of coughing, which should be considered in patients whom coughing is undesirable or contraindicated. This block is contraindicated in patients diagnosed with an unstable neck, because it induces coughing. During performance of the block, the patient should not talk, swallow, or cough, if possible.
Vascular injury – the needle does not need to be far off the midline of the cricothyroid membrane to encounter significant arterial and venous vessels. Pressure should be held over the injection site with an alcohol wipe after injection to prevent hematoma formation and subcutaneous emphysema
Structural injuries - surrounding structures, including the posterior tracheal wall and vocal cords can be damaged, especially if the needle is not stabilized during injection of the local anesthetic, or not removed immediately!
Intravascular injection - aspiration should be performed prior to the injection of local anesthetic.
Systemic toxicity - can occur quickly when several different techniques are used. As with all regional techniques, there is risk of systemic toxicity if maximum dosages of local anesthetics are exceeded. Topical anesthetics enter the circulation more quickly than when injected into tissues, and can be absorbed in the respiratory and GI tracts. Local anesthetics should be carefully measured with a syringe or cup (when able) to monitor the dosages the patient is receiving. Concentrations should be considered when using sprays or other such preparations. The lowest concentration possible should be used to minimize the risk of toxicity.Methemoglobinemia – occurs when the ferrous molecule in hemoglobin is changed to its ferric state with essentially ionic bonds by oxidation. Injury or toxic agents convert abnormally large amounts of hemoglobin to methemoglobin, which does not function reversibly as an oxygen carrier. It may result in cyanosis, and many other signs and symptoms, progressing to stupor, coma and death.
The risk if increased with airway blocks because more than one technique is frequently performed. *Thus, the combined dosages administered should be kept track of to avoid the risk of systemic toxicity.
Assessment of Block Efficacy: as with all of the airway blocks, the efficacy of is evaluated by blunting of airway reflexes such as coughing and gagging, and diminished pain and cardiovascular response to instrumentation of the airway.