ANT210L Introduction to Airway Management Notes

Anatomy and Physiology of the Airway

  • Instructor: Muhammad K. Muhammad, Mrs. of Anesthesia Technology, College of Healthcare Technologies
  • Email: Muhammad.karim@auib.edu.iq
  • Meeting time: 30.1.2025 Thursday

Overview

  • 1-Anatomy and physiology of the airway
  • 2- Airway Evaluation
  • 3-Recognition of difficult airway

Introduction

  • Knowledge of anatomy is essential for airway management.
  • Anatomical considerations aid in diagnosing problems like foreign body obstruction.
  • Emergency airway procedures require quick anatomical understanding.
  • Many airway procedures, such as tracheal intubation, involve partially visible anatomical structures, requiring recognition of their spatial relationships.

The Nose

  • Functions: respiration, olfaction, filtration, humidification, and reservoir for secretions from paranasal sinuses and nasolacrimal ducts.
  • Anatomy:
    • Each side consists of a floor, roof, and medial/lateral walls.
    • The septum forms the medial wall, made of ethmoid and vomer bones, and septal cartilage.
    • The superior aspect of the septum is a thin bony plate from the cribriform plate of the ethmoid bone.
  • Pyramidal-shaped structure projecting from the midface, made of bone, cartilage, fibrofatty tissue, mucous membrane, and skin.
  • Contains the peripheral organ of smell and is the proximal portion of the respiratory tract.
  • Divided into right and left nasal cavities by the nasal septum.
  • Anterior nares: two apertures in the inferior portion.
    • Each naris is bounded laterally by an ala (wing).
  • Posterior nares open into the nasopharynx and are called choanae.
  • Nasal endotracheal tubes and nasal airways must be well lubricated.
  • Vasoconstricting solutions should be applied to the nasal mucosa before instrumentation.
  • When inserting a nasal endotracheal tube, the bevel should be parallel to the nasal septum to avoid disrupting the conchae.

Oral Cavity

  • Divided into two parts: the vestibule and the oral cavity proper.
  • Vestibule: space between lips/cheeks (externally) and gums/teeth (internally).
  • Oral cavity proper: bounded by alveolar arch, teeth, gums (anterolaterally); hard and soft palates (superiorly); tongue (inferiorly).
  • Posteriorly: communicates with palatal arches and pharynx.
  • In the posterior aspect of the mouth, the soft palate is shaped like the letter M, with the uvula as the centerpiece.
  • This structure is a useful landmark for practitioners assessing the ease or difficulty of mask ventilation or tracheal intubation.

Tonsils

  • Palatine tonsils are collections of lymphoid tissue engulfed by two soft tissue folds, the “pillars of the fauces.”
  • Anterior fold: palatoglossal arch.
  • Posterior fold: palatopharyngeal arch.
  • Lingual tonsil is situated behind the sulcus terminalis and has a cobblestone appearance.
  • Hypertrophy of pharyngeal tonsil (adenoids) can obstruct the nasal airway, necessitating mouth breathing.
  • Hearing may be impaired when the tubular tonsils become infected.
  • Hypertrophy of the lingual tonsil may cause airway obstruction, difficult mask ventilation, and difficult tracheal intubation.

Tongue

  • Muscular organ used for speech, taste, deglutition (swallowing), and oral cleansing.
  • Divided into three parts: root, body, and tip.
  • Posterior aspect: divided into two parts by the sulcus terminalis.
  • Attached to hyoid bone, mandible, styloid processes, soft palate, and walls of the pharynx.
  • In an unconscious patient, oropharyngeal musculature relaxation can cause the tongue to displace posteriorly, occluding the airway.
  • Tongue size relative to oropharyngeal space is an important determinant of tracheal intubation ease.

Pharynx

  • Musculo-membranous passage between choanae, posterior oral cavity, larynx, and esophagus.
  • Extends from the base of the skull to the inferior border of the cricoid cartilage (anteriorly) and the lower border of C6 (posteriorly).
  • Approximately 15 cm long.
  • Widest point: level of the hyoid bone.
  • Narrowest point: lower end where it joins the esophagus.
  • Gag reflex can be elicited by stimulating the posterior pharyngeal wall in a normal conscious patient.
  • Afferent and efferent limbs of the gag reflex are mediated through the glossopharyngeal (IX) and vagus (X) nerves.

Larynx

  • Boxlike structure in the anterior portion of the neck, between C3 and C6 in adults.
  • Shorter in women and children, situated at a slightly higher level.
  • Volume of 4–5 cc in adults.
  • Made up of cartilages, ligaments, muscles, mucous membranes, nerves, blood vessels, and lymphatics.
  • Average length: 44 mm in males, 36 mm in females.
  • Designed as a protective valve to prevent food and foreign substances from entering the respiratory tract.
  • Evolved into a sophisticated organ of speech when used with the lips, tongue, and mouth.
  • Voice change in males occurs at puberty when cartilages enlarge.
  • Adam’s apple is more prominent in males because the angle between thyroid laminae is smaller, and the anteroposterior diameter is greater.

Laryngeal Cartilages

Epiglottis
  • Shaped like a leaf.
  • Attached to the thyroid cartilage by the thyroepiglottic ligament at its lower end.
  • Upper, rounded part is free, lying posterior to the tongue, attached by the median glossoepiglottic ligament.
  • Recognizable bulge in the midportion of the posterior aspect called the tubercle.
  • During swallowing, laryngeal muscles contract, the epiglottis moves downward, and the glottis closes and moves upward, preventing food from entering the larynx.
  • Acute inflammation and swelling (acute epiglottitis) can cause life-threatening airway obstruction.
Thyroid Cartilage
  • Shieldlike structure.
  • Anteriorly, the two plates come together to form a notch, more prominent in men.
  • Posterior aspect of each lamina has superior and inferior horns.
  • The inferior horn has a circular facet for articulation with the cricoid cartilage.
Cricoid Cartilage
  • Shaped like a signet ring, with the bulky portion placed posteriorly.
  • Articular facets for attachment with the thyroid cartilage and arytenoids.
  • Separated from the thyroid cartilage by the cricothyroid ligament or membrane.
  • The inferior portion of the thyroid cartilage is connected to the superior border of the cricoid cartilage by the cricothyroid ligament.
  • In acute airway obstruction, the cricothyroid membrane may be penetrated with a needle, knife, or tube and connected to an oxygen source, called cricothyrotomy, the first surgical procedure to relieve asphyxiation.
  • Downward pressure on the cricoid cartilage (Sellick’s maneuver) is required to prevent passive regurgitation of gastric contents during induction of anesthesia in nonfasting patients and emergency situations.

Trachea and Bronchi

  • The trachea is a fibrocartilagenous, tubular structure, ranging between 10 and 15 cm long in adults, extending from the cricoid cartilage to the bronchial bifurcation.
  • Structurally, it consists of 18–24 C-shaped cartilages joined by fibroelastic tissue and closed posteriorly by a membranous structure consisting of nonstriated muscle, named the trachealis.
  • Approximately, one third of the trachea lies above the suprasternal notch and one third below.

Evaluation of the Airway

Factors Characterizing the Normal Airway in Adolescents and Adults
  • History of one or more easy intubations without sequelae.
  • Normal-appearing face with “regular” features.
  • Normal clear voice.
  • Absence of scars, burns, swelling, infection, tumor, or hematoma; no history of radiation therapy to head or neck.
  • Ability to lie supine asymptomatically; no history of snoring or sleep apnea.
  • Patent nares.
  • Ability to open the mouth widely (minimum of 4 cm or three fingers held vertically in the mouth) with good TMJ function.
  • Mallampati/Samsoon class I (i.e., with patient sitting up straight, opening mouth as wide as possible, with protruding tongue; the uvula, posterior pharyngeal wall, entire tonsillar pillars, and fauces can be seen).
  • At least 6.5 cm (three finger-breadths) from tip of mandible to thyroid notch with neck extended.
  • At least 9 cm from symphysis of mandible to mandibular angle.
  • Slender supple neck without masses; full range of neck motion.
  • Larynx movable with swallowing and manually movable laterally (about 1.5 cm on each side).
  • Slender to moderate body build.
  • Ability to maximally extend the atlantooccipital joint (normal extension is 35∘35^{\circ}).
  • Airway appears normal in profile.
Signs Indicative of an Abnormal Airway
  • Trauma, deformity; burns, radiation therapy, infection, swelling; hematoma of the face, mouth, pharynx, larynx, and/or neck.
  • Stridor or “air hunger.”
  • Hoarseness or “underwater” voice.
  • Intolerance of the supine position.
  • Mandibular abnormality:
    • Decreased mobility or inability to open the mouth at least three finger-breadths.
    • Micrognathia, receding chin:
      • Treacher Collins, Pierre Robin, other syndromes.
      • Less than 6 cm (three finger-breadths) from tip of the mandible to thyroid notch with neck in full extension (adolescents and adults).
    • Less than 9 cm from angle of the jaw to symphysis.
    • Increased anterior or posterior mandibular depth.
  • Laryngeal abnormalities: fixation of the larynx to other structures of the neck, hyoid, or floor of mouth.
  • Macroglossia.
  • Deep, narrow, high-arched oropharynx.
  • Protruding teeth.
  • Mallampati/Samsoon classes III and IV
  • Inability to visualize the posterior oropharyngeal structures (tonsillar fossae, pillars, uvula) on voluntary protrusion of the tongue with mouth wide open and the patient seated.
  • Neck abnormalities:
    • Short and thick.
    • Decreased range of motion (arthritis, spondylitis, disk disease).
    • Fracture (possibility of subluxation).
    • Obvious trauma.
  • Thoracoabdominal abnormalities:
    • Kyphoscoliosis.
    • Prominent chest or large breasts.
    • Morbid obesity.
    • Term or near-term pregnancy.
  • Age between 40 and 59 years.
  • Gender (male).
  • Snoring and sleep apnea syndrome.

Difficult Airway

Risk factors for difficult intubation include the following:
  • Mouth opening less than 4 cm
  • Thyromental distance less than 6 cm
  • Mallampati Class III or higher
  • Neck movement less than 80%
  • Inability to advance the mandible (prognathism)
  • Body weight greater than 110 kg
  • Positive history of difficult intubation