AIRWAY PHYSICS

• Poiseuille’s law

  • Q=ΔPπr48ηl; r = Radius of airway

  • Flow (Q) is proportional to the radius to the fourth power; incremental changes in the radius cause exponential decreases in airflow

• Bernoulli’s principle

  • Increased airflow results in a decrease in pressure

  • Narrowed airway → Increased airflow speed → Decreased intraluminal pressure (vacuum) → Further collapse of walls of lumen

• Stridor – high-speed airflow through collapsed tissues causes vibration and a resonance, resulting in a sound

NOISY BREATHING

• Physical obstruction of the airway is associated with noise on inspiration or expiration, depending on the site and nature of the lesion

• Stridor is not only audible, but also visible

  • Examiner should be able to visualize site of obstruction while noise is being made

  • Requires adequate instrumentation techniques of the airway

• Isolated tachypnea (i.e., without stridor) is not a sign of airway obstruction

NASAL OBSTRUCTION

• Piriform aperture stenosis

  • Bony narrowing of the anterior nasal vestibule in neonates; results in airway-related respiratory distress and feeding problems

  • Diagnosed by computerized tomography (CT) scan showing <8 mm patency between nasal processes of maxillary bone

  • Can be associated with holoprosencephaly (central incisor) or choanal atresia

  • Treatment: sublabial approach to nasal vestibule with high-powered drill reduction of nasal process of maxillary bone

• Choanal atresia/stenosis

  • Incomplete or uncannulated opening from the nose to the nasopharynx in neonates; results in airway-related respiratory distress

  • CHARGE syndrome (coloboma, heart defects, atresia choanae, growth retardation, genital abnormalities, and ear abnormalities)

  • May go undiagnosed if unilateral

  • Treatment: transnasal or transpalatal resection of posterior obstructive tissues

PHARYNGEAL OBSTRUCTION

• Adenotonsillar disease

  • Most common cause of obstructive sleep apnea (OSA) in children

  • Diagnosed by direct visualization on exam and attended nocturnal polysomnogram

  • Treatment: adenotonsillectomy adequately treats >80% of patients with pharyngeal airway obstruction

• Pharyngomalacia

  • Poor pharyngeal muscle tone, results in collapse of tissues and obstruction with stertor

  • Treatment: noninvasive positive pressure ventilation (continuous or bilevel)

• Glossoptosis/macroglossia (Figure 20-1)

  • Tongue and tongue base obstruction of the airway

  • Pierre-Robin’s sequence, Down’s syndrome, lingual tonsil hypertrophy, isolated micrognathia, Ludwig’s angina (anterior floor of mouth abscess)

  • Treatment: alleviate obstruction by resection, advancement, or bypass (i.e., tracheotomy)

• Pharyngeal obstruction results primarily in sleep apnea symptoms