Tracheal Intubation and Endoscopic Anatomy

Published on 16/04/2015 by admin

Filed under Surgery

Last modified 22/04/2025

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 14356 times

Chapter 45

Tracheal Intubation and Endoscopic Anatomy

Airway Anatomy

The pulmonary system consists of lungs and a series of airways that are subdivided into upper and lower segments.

Upper Airway

The upper airway consists of the nose, mouth, pharynx, and larynx. There are three pharyngeal segments: (1) nasopharynx, posterior to the soft palate; (2) oropharynx, posterior to the tongue from the tip of the uvula to the tip of the epiglottis; and (3) laryngopharynx, posterior to the epiglottis (Fig. 45-1). The pharyngeal segments are collapsible because the anterior and lateral walls lack bony support.

Inspiratory patency of the pharynx is maintained primarily by contraction of the tensor palatine, genioglossus, and hyoid bone muscles. Loss of muscle tone leads to pharyngeal collapse. During general anesthesia or intravenous sedation, the upper airway becomes obstructed because of a decrease in the anteroposterior diameter of the pharynx at the level of the soft palate and epiglottis. Many anesthetic agents and sedative drugs diminish the action of pharyngeal dilator muscles, which promotes pharyngeal collapse and airway obstruction.

Larynx

The larynx serves as the connecting structure between the upper and lower airways (Fig. 45-2). The adult larynx extends from the 4th to the 6th cervical vertebra, and it is composed of nine cartilages, with six paired and three single. The three single cartilages include the thyroid, cricoid, and epiglottis. The paired arytenoid cartilages secure the vocal cords to the larynx. The endolarynx is constructed of two pairs of folds that form the supraglottis and glottis.

The internal and external laryngeal muscles control vocal cord length and tension and movement of the larynx as a whole. These muscles aid in swallowing, respiration, and vocalization and are integral in preventing aspiration into the trachea and lower airway. The hyoid bone suspends and anchors the larynx.

Note the location of the superior laryngeal nerve (important for nerve block anesthesia) adjacent to the hyoid bone (Fig. 45-2). Motor innervation of the laryngeal muscles is through the superior laryngeal nerve (cricothyroid muscle) and recurrent laryngeal nerve (remainder of laryngeal muscles). Stimulation of the supraglottic region, especially where the piriform recesses blend with the hypopharynx, can result in laryngospasm with complete glottic closure.

Nose and Nasopharynx

Nasotracheal intubation is an alternative approach to orotracheal intubation. The two nasal fossae extend from the nostrils to the nasopharynx. The nasal fossae are divided by the midline cartilaginous septum and medial portions of the lateral cartilages (Fig. 45-3, A). The nasal fossa is bounded laterally by inferior, middle, and superior turbinate bones. The mucosa covering the middle turbinate is highly vascular, receiving its blood supply from the anterior ethmoid artery, and also contains a large plexus of veins. The middle turbinate is susceptible to avulsion by trauma and is associated with massive epistaxis. The paranasal sinuses (sphenoid, ethmoid, maxillary, and frontal) open into the lateral wall of the nose. The inferior turbinate usually limits the size of the nasotracheal tube.

Lower Airway

The lower airway consists of the trachea, bronchus, bronchioles, respiratory bronchioles, and alveoli. The adult trachea, which begins at the cricoid cartilage opposite the 6th cervical vertebra, contains 16 to 20 cartilaginous rings. The posterior part of the trachea is devoid of cartilage (Fig. 45-3, B). Pressure over the cricoid cartilage (Sellick maneuver) is often applied during rapid-sequence induction and intubation (RSI) to minimize the risk of aspiration in unfasted (full stomach), anesthetized, and paralyzed patients before intubation. However, cricoid pressure may distort airway anatomy, making intubation more difficult.

The trachea divides into two bronchi at the carina. The right and left bronchi are positioned differently; the right extends vertically from the trachea, which allows for an easier pathway for aspirate and foreign particles to enter. This accounts for the higher incidence of unintentional right main bronchus intubations.

Bronchial divisions continue down the pulmonary pathway into increasingly smaller airways. The alveoli complete the final phase of the pulmonary system and constitute the area of primary gas exchange, where oxygen enters the bloodstream and carbon dioxide is removed.

Indications for Intubation

Inadequate oxygenation and ventilation can rapidly lead to brain injury or death. Initial ventilatory support is usually accomplished by relieving airway obstruction (suction, chin lift, jaw thrust, oral airway, nasal airway) and bag-mask ventilation (BMV) with 100% oxygen. The oral airway is designed to hold the tongue away from the posterior pharyngeal wall and prevent the tongue from obstructing the glottis.

The nasopharyngeal airway is an uncuffed, trumpetlike tube that is inserted through the nasopharynx, bypassing the oropharynx and mouth. The distal end is just superior to the epiglottis and inferior to the base of the tongue. The proximal end has a flange to prevent the airway from migrating into the nose (Fig. 45-4, A).

Indications for intubation include respiratory failure, severe pulmonary, or multisystem injury, depressed level of consciousness, cardiac arrest, shock, and inadequate BMV. Advantages of intubation include maintenance of a definitive airway; ability to deliver positive pressure ventilation, high inspired oxygen concentration, and positive end-expiratory pressure (PEEP); and decreased risk of aspiration.

Preintubation Airway Examination

Airway examination should include anatomic and pathologic factors that can predict likelihood of a difficult airway (Fig. 45-4, B). Anatomic factors that increase tracheal intubation difficulty include Mallampati class III (only soft palate visible when patient opens mouth wide and protrudes tongue), limited mouth opening, protruding maxillary incisors, narrow mouth width, cleft lip/palate, small oral cavity, large tongue, tumors, trauma, and infection.

The American Society of Anesthesiologists (ASA) defines the difficult airway as that clinical situation in which a conventionally trained anesthesiologist experiences difficulty with BMV, intubation, or both. Difficult direct laryngoscopy occurs when it is not possible to visualize any portion of the vocal cords after multiple attempts at conventional laryngoscopy. Difficult intubation occurs when intubation requires multiple attempts. Failed intubation occurs when placement of the endotracheal tube (ETT) fails after multiple attempts.

Pathologic factors that further challenge practitioners include tumors, deep fascial plane infections of the face or neck, burns, congenital anomalies, airway trauma, thermal and inhalation injury, and cervical spine trauma (Fig. 45-4, C-E).

Laryngoscopy

After suitable anesthesia is given, an appropriate-sized laryngoscope blade is inserted to the right of the patient’s tongue, which must be displaced and compressed (Fig. 45-5, A). Head extension and the sniffing position facilitate line of sight for the practitioner to insert the tube through the vocal cords. With infants and neonates, use of a straight blade is preferred. Because of the proximity of the upper airway to the cervical spine (see Fig. 45-1), some movement of the atlanto-occipital and atlanto-axial segments generally occurs during laryngoscopy.

With the GlideScope, the blade is introduced into the mouth in the midline and rotated around the tongue. The camera, embedded in the blade, points upward to provide a view of the glottis. An appropriately shaped stylet is necessary to deliver the ETT to the larynx.

During intubation, different views of the glottic opening are achieved, depending on patient anatomy and practitioner skills (Fig. 45-5, B). Pressure over the thyroid cartilage often improves the view at laryngoscopy. The ETT is introduced through the vocal cords until the cuff disappears. Ventilation is confirmed by sustained presence of end-tidal carbon dioxide, auscultation of bilateral breath sounds with absence of air over the epigastrium, and chest rise. The tube is securely taped or tied at the appropriate depth. In adults, an average distance of 20 to 24 cm is required to place the distal end of the tube in the midtracheal position.

Malpositioning may occur by inserting the ETT into the esophagus or by advancing the tube too distal into the trachea past the carina (endobronchial intubation).

Flexible Fiberoptic Bronchoscopy

Flexible fiberoptic bronchoscopy (FOB) intubation is often done in conscious, spontaneously breathing patients with a known or suspected difficult airway (e.g., unstable cervical spine, cooperative patient). A silicone spray or other lubricant is helpful to ensure easy advancement of the ETT over the FOB. Jaw thrust may improve visualization of anatomic structures. The Ovassapian airway cannula is useful as a guide for traversing the oral cavity with the oral approach. FOB may also be done via a laryngeal mask. Thermosoftening of the ETT (35° C saline) improves navigability through the nasal passageways and reduces epistaxis and nasal damage with the nasal approach.

Nasotracheal Approach

As the nose is entered with the FOB, it is imperative to visualize the inferior and middle turbinates (Fig. 45-6). As the FOB is advanced from the anterior nasal cavity to the posterior nasal cavity, the following anatomic structures should be visualized:

With continued advancement of the scope, the adenoids and opening of the eustachian tubes can be visualized. Once the FOB is at this level, the posterior pharynx and base of the tongue should come into view, with the epiglottis and glottic opening again just distal. The glottic opening, vocal cords, and tracheal rings are visualized as with the oral approach. Maneuvers to optimize the view are similar as with oral FOB.

Careful attention must be given to the location of the middle and inferior turbinates. These landmarks determine the borders of the two paths usually taken by a tracheal tube passing through the nasal passage. Standard practice is to use the lower pathway to avoid structures of the ethmoid bone and cribriform plate.

Suggested Readings

American Society of Anesthesiologists. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists task force on management of the difficult airway. Anesthesiology. 2013;118:251–270.

Cooper, RM, Pacey, JA, Bishop, MJ, McCluskey, SA. Early clinical experience with a new videolaryngoscope (GlideScope) in 728 patients. Can J Anaesth. 2005;52:191–198.

Crosby, E. Airway management after upper cervical spine injury: what have we learned? Can J Anesth. 2002;49:733–744.

Crosby, ET, Cooper, RM, Douglas, MJ, et al. The unanticipated difficult airway with recommendations for management. Can J Anaesth. 1998;45:757–776.

Kheterpal, S, Han, R, Tremper, KK, et al. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology. 2006;105:885–891.

Smith, CE, DeJoy, S. New equipment and techniques for airway management in trauma. Curr Opin Anaesthesiol. 2001;14:197–209.

Related posts:

Chest Tube Placement Right Colectomy Pyloromyotomy for Pyloric Stenosis Laparoscopic and Open Cholecystectomy Splenectomy Gastrectomy