Recurrent laryngeal nerve block

Transtracheal anesthesia / recurrent laryngeal nerve block
Anatomy
The recurrent laryngeal nerve is the branch of vagus nerve (cranial nerve X) that supplies all intrinsic muscles of the larynx except cricothyroid. There are two, right and left recurrent laryngeal nerve. The nerve emerges from the vagus nerve at the level of arch of aorta and then travel up the side of the trachea to the larynx. The left recurrent laryngeal nerve loops under the arch of aorta while the right nerve travels directly upwards.
The recurrent laryngeal nerve supply sensation to the larynx below the vocal cords, give cardiac braches to the deep cardiac plexus and branches to the trachea, esophagus and inferior constrictor muscles. The posterior cricoarytenoid muscle which opens the vocal cord is innervated by this nerve.
Indications
The indications of recurrent laryngeal nerve block are:
• Awake laryngoscopy
• Fiberoptic and/ or retrograde intubation
• Abolition of gag reflex or hemodynamic response to laryngoscopy or bronchoscopy.
The transtracheal injection of lidocaine performed prior to induction of general anesthesia is an effective alternative to intraoperative propofol infusion when long acting muscle relaxants are to be avoided.
Source: Sunil Ranjan, Nitu Puthenveettil, Krishnakumar Thankappan, Jerry Paul. Transtracheal lidocaine injection reduces the anesthetic requirements in brachial plexus surgeries.  Anesthesia essays and researches. 2013. Vol. 7 Issue 1, pages 110-115.
The transtracheal injection blocks the sensory innervations supplied by the vagus nerve via the recurrent laryngeal nerve. Sensory innervation of the vocal cord and trachea is supplied by recurrent laryngeal nerve. This block can be achieved by:
1. Inhalation of local anesthetic
2. Transtracheal block
3. It can also be achieved by spraying the local anesthetic via the injection port of the fibreoptic bronchoscope
Source: Nibedita Pani, Shovan Kumar Rath. Regional & topical anesthesia of upper airways. Indian Journal of Anesthesia 2009; 53(6): 641-648.
Lidocaine is used for this block and is rapidly absorbed into the systemic circulation via the trachea. Maximum safe dose of lidocaine in the trachea (atomizer + transtracheal) is 4mg/kg.
 
The two different methods of achieving upper airway anesthesia for awake fiberoptic intubation  were compared in patients undergoing surgery for cervical spine instability. Topical anesthesia was administered nebulized 4% lidocaine (20 ml) via the oropharynx plus transtracheal injection of 4% lidocaine (3 ml). nerve block patients underwent bilateral glossopharyngeal and superior laryngeal nerve blocks with 2% lidocaine plus trans tracheal injection of 4% lidocaine (3 ml). Both the  techniques were found to be safe and effective and offer alternatives when patient with cervical spine disorders require awake oral fiberoptic intubation of the trachea.
Source:  Daniel K Reasoner, David S Warner, Michael M Todd, Scott W Hunt, and Jerry Kirchner. A comparison of anesthetic techniques for awake intubation in neurosurgical patients. Journal of Neurosurgical Anesthesiology. 1995. Vol 7, No 2. Pages 94-99.
Procedure
• Cricothyroid membrane is located between the thyroid and cricoids cartilage.
• It is identified as spongy fibromuscular band between the thyroid and cricoids cartilages
• A 22 or 20 gauge needle attached to a 10 ml syringe is passed perpendicular to the axis of the trachea and pierces the membrane
• 2 ml of 2-4% lidocaine is injected into the trachea/ larynx at the end of normal expiration.
• Instillation of local anesthetic results in coughing
• Through coughing, the local anesthetic is dispersed, diffusely blocking the sensory nerve endings of recurrent laryngeal nerve. The motor functions completely remain unaffected
 
Complications:
• Gastric aspiration
• Risk of coughing
• Vascular injury
• Structural injuries: injury to posterior tracheal wall and vocal cords
• Intravascular injection
• Systemic toxicity
• Methemoglobinemia
The 2 possible complications of transtracheal anesthesia are cellulitis of the neck and breakage of the needle.
Source: John Adriani, John Parmley. Complications of transtracheal anesthesia. The American Journal of Surgery. July 1952. Vol 84, Issue 1, Pages 11-12.
Nocardia cellulitis.
Source: David C Green, Gail B Strait. A complication of transtracheal anesthesia: Nocardia Cellulitis. The annals of Thoracic Surgery. December 1969. Vol 8, Issue 6. Pages 561-563.
 
Assessment of the block
‚ÄčThe block is evaluated by
• Blunting of airway reflexes like coughing and gagging
• Diminished pain and cardiovascular response to instrumentation of the airway