Anatomy of the Airway

Transcription

1 Anatomy of the Airway Nagelhout, 5 th edition, Chapter 26 Morgan & Mikhail, 5 th edition, Chapter 23 Mary Karlet, CRNA, PhD Airway Anatomy The airway consists of the nose, pharynx, larynx, trachea, and lower airways I. Nose - heat, humidification, filtration Except with extreme cold, nose warms inspired air to body temperature Nearly 100% humidification Airway Anatomy II. Pharynx wide muscular tube that is a part of both the respiratory tract and the alimentary tract Upper border is base of skull; lower border cricoid cartilage (C-6) where it continues with esophagus 1. Nasopharynx: nasal passage soft palate 2. Oropharynx: soft palate epiglottis 3. Laryngopharynx (hypopharynx): epiglottis level of C-6 (beginning of esophagus) 1

2 Nasopharynx: opens anteriorly to nasal cavity Oropharynx: opens anteriorly to mouth Laryngopharynx: opens anteriorly to larynx Palatine, Lingual, and Adenoid Tonsils Palatine tonsils Airway Anatomy III. Larynx: Extends C-3 to C-6 vertebrae Consists of: One bone (hyoid) 9 cartilages Muscles, Ligaments, Membranes Hyoid bone chief support for larynx via thyrohyoid membrane Thyroid and cricoid cartilages major framework Protective structure that prevents aspiration during swallowing Site of vocalization 2

3 Airway Anatomy 9 Laryngeal Cartilages Unpaired Cartilages Epiglottis: separates oropharynx from hypopharynx; covers entrance to larynx Thyroid: vc attaches to anterior thyroid cartilage Cricoid (C-6): ring of cartilage immediately below thyroid cartilage; marks the beginning of trachea; below the vocal cords; narrowest in age < 10 Larynx Vocal cords attached anteriorly to thyroid cartilage and posteriorly to arytenoids Includes glottis = space between vocal cords In adults, glottis smallest airway circumference In child < age 10, cricoid cartilage smallest circumference Airway Anatomy 9 Laryngeal Cartilages Paired Cartilages Arytenoid (2): attached to posterior ends of vc Corniculate (2) embedded in aryepiglottic Cuneiform (2) folds 3

4 Membranes of the Larynx Thyrohyoid membrane suspends the larynx from the hyoid bone Cricothyroid membrane recommended site for emergency establishment of airway; also site of transtracheal block Muscles of the Larynx Intrinsic Muscles (9) 1. Post. Cricoarytenoid (2): Abducts (opens) glottis 2. Lat. Cricoarytenoid (2) Adducts (closes) glottis 3. Transverse or Interarytenoids between arytenoids helps close glottis 4. Cricothyroids (2) Regulates tension, elongates and tightens cords 5. Thyroarytenoids (2) Regulates tension, shortens and loosens the cords Extrinsic Muscles (3) 1. Sternohyoid Depresses larynx 2. Thyrohyoid Elevates larynx 3. Inferior constrictor Constricts pharynx 4

5 Innervation to the Upper Airway 1. Trigeminal n. Sensory innervation to the nasal mucosa, anterior ⅔ s of tongue, hard and soft palate 2. Glossopharyngeal n. Sensory innervation to the oropharynx, undersurface of soft palate, and posterior ⅓ of tongue, tongue side of epiglottis, tonsils, and vallecula Innervation to the Upper Airway 3. Vagus n. innervates distal airways, epiglottis and below Superior laryngeal n. - sensory to laryngeal side of epiglottis vocal cords, arytenoid cartilages, mucus membranes immediately above larynx; motor to cricothyroid m. Recurrent (inferior) laryngeal n. - sensory to mucus membranes below vc; motor to all laryngeal muscles except cricothyroid m. Sensory Innervation of the Upper Airway V2 = maxillary division of Trigeminal nerve (sphenopalatine nerve) V3 = mandibular division of Trigeminal nerve (lingual nerve) 5

6 Effect of laryngeal nerve injury Superior laryngeal n. a) unilateral b) bilateral Recurrent laryngeal n. a) unilateral b) bilateral acute c) bilateral - chronic a) minimal effects b) hoarseness; tiring of voice a) hoarseness b) stridor or aphonia, respiratory distress c) compensatory mechanisms often prevent resp. distress Tracheobronchial Tree Major function to conduct air alveoli Lined by ciliated columnar epithelium 23 generations or divisions cross-sectional area diameter Trachea Extends from inferior larynx to carina; C6 T5 Distance from incisors to larynx = 13 cm; distance from larynx to carina = 13 cm distance from incisors to carina = 26 cm Diameter approximated by diameter of index finger Horseshoe-shaped cartilage and fibrous muscle tissue At T5 (carina) divides into two primary bronchi 6

7 Trachea The trachea is not fixed it moves with head and neck movement Neck flexion trachea moves upward ETT moves downward endobronchial intubation possible Neck extension trachea moves downward and ETT moves upward extubation possible Trachea moves upward if patient turns head right or left Tracheobronchial Tree The bronchi (generation #1) Right mainstem bronchus: Shorter (2.5 cm), wider, and more vertical (25 angle) Left mainstem bronchus: Longer (5 cm) and more horizontal (45 angle) Cartilagenous rings down to bronchioles maintain rigidity With decreased cartilage sm.m. Wall of bronchioles almost entirely sm.m. down to respiratory zone Terminal bronchioles last structures perfused by bronchial circulation and the end of conducting airways 7