Anesthesia for Ear, Nose, Throat, and Maxillofacial Surgery Part 1.pdf

Anesthesia for Ear, Nose, Throat, and Maxillofacial Surgery Part I FUNCTIONAL ANATOMY OF THE HEAD AND NECK Prof. Albert J. Albors DNP, APRN, CRNA University of Puerto Rico Medical Sciences Campus Nurse Anesthesiology Program 1 Objectives • Describe the pertinent anatomy and physiology of the hea...

Anesthesia for Ear, Nose, Throat, and Maxillofacial Surgery Part I FUNCTIONAL ANATOMY OF THE HEAD AND NECK Prof. Albert J. Albors DNP, APRN, CRNA University of Puerto Rico Medical Sciences Campus Nurse Anesthesiology Program 1 Objectives • Describe the pertinent anatomy and physiology of the head and neck for the anesthetist. • Reviews specialized anesthetic considerations, reviews surgical and anesthesia equipment used during ENT procedures. • Analyzes some of the common pharmacologic agents used for ENT procedures. • Discusses principles of anesthesia for ENT. 2 Introduction A fundamental knowledge of the anatomic and physiologic function of the structures of the head and neck is essential for dealing with the myriad decisions arising perioperatively during these procedures. Commonly, ENT surgical procedures are performed because the anatomic structures are abnormal, distorted, or deviated. Having a working knowledge of the structures and their relationships before subjecting the patient to respiratory changes produced by anesthesia is imperative. 3 Anatomy Review The anatomic structures of the head and neck and their relationships are complex. The sensory and motor supply of the upper airway originates from cranial nerves and includes the trigeminal, glossopharyngeal, facial, and vagus nerves. Understanding the sensory supply is required to provide sufficient local and regional anesthesia. Likewise, motor function evaluated during and after surgical procedures may indicate trauma or damage to muscles. The anatomic relationships regarding the nasopharynx, oropharynx, laryngopharynx, and lower airway structures such as the larynx, cricoid, thyroid, and vocal cords provide a basis for directing and providing care for the patient receiving ENT surgery. 4 5 Nose The nose is a major anatomic structure that is responsible for warming, filtering, and providing humidity to the air taken in during inspiration. The structures of the nose include the external nose, the nasal cavity, and frontal, maxillary, and ethmoid sinuses. The nares or nostrils are separated by the septum. The lateral margins of the nares are cartilaginous structures and extend posteriorly over the hard palate leading to a confluence at the soft palate, oropharynx, and base of the tongue. The oropharynx rests superior to the epiglottis, vocal cords, larynx, and trachea. 6 Nose Externally, the nose is composed largely of cartilage supported primarily by soft connective tissue and delicate mucous membranes, as is the nasal septum. The nasal cavities are hollow structures formed by a floor, roof, lateral wall, and the septum. The lateral aspects of the nasal cavities contain concha, or turbinates. The turbinates are highly vascular and are divided into three separate compartments: the superior, middle, and inferior. The turbinates greatly increase the surface area of the nasal cavities, aiding in filtration and humidification of inspired gases. The extensive vascular supply of the turbinates may lead to severe bleeding if the nasal airway or nasoendotracheal tube is not inserted along the superior margin of the hard palate. 7 The pharynx is composed of the terminal end of the nasopharynx, the oropharynx, and laryngopharynx or hypopharynx extending to the sixth cervical vertebra. Pharynx The medulla oblongata inhibits respiration with swallowing; the pharynx then serves as a muscular tube that constricts, allowing the passage of food. The pharynx allows the smooth passage of air and functions as a modulator for the voice. 8 Nasopharynx The nasopharynx is continuous with the internal nasal cavities and extends to the soft palate. The nasopharynx communicates with the oropharynx and forms the posterior aspect of the throat. 9 Oropharynx Major structures of the oropharynx include the base of the tongue, soft palate, uvula, and lymphatic structures (tonsils). The tonsils are the most sensitive areas of the oropharynx. Beginning with the anterior margin and progressing bilaterally and posteriorly, the oropharynx is defined by the soft palate, base of the tongue, uvula, palatine tonsils, and adenoids, forming Waldeyer tonsillar ring. 10 The larynx is a rigid organ composed of three paired and three unpaired cartilages (arytenoid, corniculate, and cuneiform; and thyroid, cricoid, and epiglottis, respectively) and is supported by the hyoid bone. Larynx This hollow structure forms a reservoir distal to Waldeyer tonsillar ring and provides the connection of the oropharynx to the trachea. The primary functions of the larynx are vocalization and articulation; secondarily, it provides protection of the airway and allows respiration. In the adult, the area of the vocal cords, or rima glottidis, is the narrowest portion of the larynx. In children, the cricoid ring has traditionally been regarded as the narrowest portion of the airway until approximately 10 years of age. 11 12 Special considerations Specific nervous system structures of the head and neck are noteworthy because of their superficial location or proximity to operative sites. Surgeons may use audible or visual nerve-locating devices to find these nerves and their appropriate branches. To accurately locate these nerves, neuromuscular blocking agents may need to be avoided during the maintenance of certain general anesthetics. 13 Facial Nerve The facial nerve (VII) has six major branches: four anterior (temporal, zygomatic, buccal, and mandibular), one inferior (cervical), and one posterior (posterior auricular) branch. The facial nerve located at the tragus of the ear is the motor and sensory supply to the muscles for facial expressions. The zygomatic branch exits the skull via the stylomastoid foramen and advances anteriorly over the maxilla. The chorda tympani branch of the facial nerve conveys taste from the anterior two-thirds of the tongue, and the more superficial tribranched facial nerve controls facial expression. 14 Trigeminal Nerve The trigeminal nerve begins at the gasserian ganglion and divides into three branches: V1:ophthalmic V2: maxillary V3: mandibular All three divisions provide sensory and motor innervation to the nose, sinuses, palate, and tongue. They aid in the motor control of the face and in mastication. 15 Glossopharyngeal nerve The glossopharyngeal nerve provides motor and sensory innervation for the base of the tongue and nasopharynx and oropharynx. The glossopharyngeal nerve is responsible for eliciting the gag reflex during instrumentation of the posterior pharynx and vallecula. 16 Vagus nerve The superior laryngeal nerve and recurrent laryngeal nerve (RLN) are both branches of the vagus (X). The superior laryngeal nerve descends to the hyoid bone and then branches into the internal laryngeal nerve, which passes through the thyrohyoid membrane, and the exterior laryngeal nerve, which descends over the lateral thyroid cartilage to the distal trachea. 17 Recurrent Laryngeal Nerve The RLN ascends from the vagus up the distal trachea, passing through the cricothyroid ligament into the proximal trachea and vocal cords. The RLN lies between the trachea and esophagus and supplies sensory innervation to the trachea and area below the vocal cords. This branch of the vagus nerve also affects vocal cord closure and sensory function up to the inferior aspect of the epiglottis. Stimulation of the epiglottis with the tip of a straight laryngoscope, blades, suction catheters, and placement of an ETT in the trachea can produce a vagal response. 18 19 20 References Nagelhout JJ, Elisha S, Heiner JS, eds. (2020). Nurse anesthesia (7th ed.). Philadelphia: Elsevier. Apex Anesthesia Review (2023) 21