Superior laryngeal nerve
Superior laryngeal nerve is the branch of vagus nerve which arises from the middle of the ganglion nodosum and receives the branch from the superior cervical ganglion of the sympathetic.
It descends by the side of the pharynx, behind internal carotid artery and is divided into two branches:
a) External laryngeal nerve
b) Internal laryngeal nerve
Its internal branch supplies sensory innervations to the base of tongue, posterior surface of the epiglottis, aryepiglottic folds and the arytenoids.
The internal branch originates from superior laryngeal nerve of vagus nerve lateral to the greater cornu of hyoid bone. In majority of the patients it passes 2-4 mm inferior to greater cornu of hyoid bone and pierces the thyrohyoid membrane then it travels under the mucosa in the pyriform sinus.
• Bilateral superior laryngeal nerve block is used to facilitate diagnostic laryngoscopy and bronchoscopy
• It allows comfortable placement of tracheal tube in patients undergoing endotracheal intubation
Local glossopharyngeal and superior laryngeal nerve block is used for peroral endoscopies (esophagoscopies, bronchoscopies and combined bronchoesophagoscopies). The technique allows easy insertion of rigid and flexible scopes or awake tracheal intubation of conscious patients.
Source: Tom R DeeMeester, David B Skinner, Richard H Evans, Donald W Benson. Local nerve block anesthesia for peroral endoscopy. The Annals of Thoracic Surgery. September 1977. Vol 24, No.3.
2 cases of superior laryngeal neuralgia were successfully treated with superior laryngeal nerve block with high concentration of lidocaine, after treatment with carbamazepine failed.
Source: Takahashi Sato K, Suzuki M, Izuha A, Hayashi S, Isosu T, Murakawa M. Two cases of superior laryngeal neuralgia treated by superior laryngeal nerve block with high concentration of lidocaine. J Clin Anesth 2007 May; 19(3): 237-8.
Superior laryngeal nerve block can be used for treatment or prevention of laryngospasm and stridor.
Source: Monso A, Riudeubas J, Palanques F, Braso JM.A new application of superior laryngeal nerve block: treatment or prevention of laryngospasm and stridor. Reg Anesth Pain Med. 1999 Mar-Apr;24(2):186-7.
Superior laryngeal nerve block acts as a supplement to total intravenous anesthesia for rigid laser bronchoscopy in the patient with myasthenic syndrome.
Superior laryngeal nerve block
The steps for superior laryngeal nerve block include:
• Locate the hyoid bone
• 1 cm below each greater cornu (where internal branch of superior laryngeal nerve penetrates the thyrohyoid membrane)
• Infiltrate 3 ml 2% lignocaine
• Feel the pop as the needle penetrates the membrane
Superior laryngeal nerve block using ultrasound technique
Since visualization of superior laryngeal nerve is often unsuccessful, hyoid image or superior laryngeal artery are used as ultrasound landmarks for blockade of nerve.
A 8-15 MHz transducer HST15-8/20 linear probe (Ultrasonix) has improved image processing and resolution and identify and target superior laryngeal nerve accurately under ultrasound guidance.
Source: Balvinder Kaur, Raymond Tang, Andrew Sawka, Himat Vaghadia. Superior laryngeal nerve block using a novel ultrasound technique. Department of Anesthesia. Vancouver General Hospital, Vancouver, BC, Canada.
Using ultrasound imaging for nerve block reduce the amount of local anesthetic required, improves the success rate, reduce the time to perform the block, and reduce the complication rate
Source: Manikandan S, Neema PK, Rathod RC. Ultrasound guided bilateral superior laryngeal nerve block to aid awake endotracheal intubation in a patient with cervical spine disease for emergency surgery. Anaesth Intensive Care. 2010 Sept;38(5): 946-8
• Local anesthetic toxicity can occur due to rapid uptake of LA as the mucosa of upper airway is well perfused
• Aspiration can occur in patients as the block abolishes the airway reflex
• Methemoglobinemia which may result in cyanosis, stupor, coma and death of the patient
• Hypotension and bradycardia. A study suggested that hypotension and bradycardia occurred in 2 patients after superior laryngeal nerve block for awake tracheal intubation. Both the patients required treatment of anticholinergic drugs and iv infusions.
Source: Wiles JR, Kelly J, Mostafa SM. Hypotension and bradycardia following superior laryngeal nerve block. Br J Anaesth. 1989 Jul; 63(1):m125-7.
• Convulsion following left superior laryngeal nerve block for endotracheal intubation
Source: Hsu CH, Lin TC, Yeh CC, Ho ST, Wong CS. Convulsion following superior laryngeal nerve block: A case report. Acta Anaesthesiol Sin. 2000 Jun; 38(2): 93-6.