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Upper Airway Obstruction

The Pediatric Airway

  • Important differences between the adult and pediatric airway:
    • Pediatric tongue is larger in proportion to the mouth/pharynx
    • The pediatric glottis is more anterior and superior (Epiglottis is at C1 at birth, C3 by 6 months of age, C5-6 by adolescence)
    • The narrowest portion of the pediatric airway is the subglottic space (specifically, the cricoid, and often the area of subglottic stenosis development due to the complete ring that likely leads to greater likelihood of mucosal compression) whereas the glottic opening (vocal cords) is the most narrow portion of the adult airway
    • Epiglottis is larger and floppier in children
    • While not truly obligate nose-breathers, infant's nares are smaller and more easily occluded by mucus or edema
Figure 1: Adult vs. Pediatric Airway: Major Differences


(From Fuhrman and Zimmerman, Pediatric Critical Care, 2016)
  • Edema disproportionately affects airway resistance, and thus, work of breathing, in pediatric patients. See Figure 2 for a comparison of what 1 mm of circumferential edema does in terms of airway resistance to an infant and an adult

Pathophysiology

  • Upper airway obstruction can occur for a variety of causes, but fundamentally, leads to increased airway resistance and thus, increased work of breathing or ineffective breathing. 
    • Remember, V=IR (Ohm's law) or Voltage= Current X Resistance. For the airway, Voltage is Delta Pressure or the pressure differential that must be generated to move air. I = flow or the liters/minute of flow that occurs. R = resistance, or airway resistance which is described by Poiseuille's Law. Hence, the more resistance or the more flow that needs to be generated, the higher the delta P or work of breathing.
      Poiseuille's Law Describing Resistance:  
      • R= 8lη/π r4  where l is the length of the tube, η= viscosity, and r= radius. Hence, the longer the tube and the more narrow the tube, the more resistance exists
  • Conditions that can lead to upper airway obstruction include:
    • Croup (classically due to parainfluenza, characterized by barking cough) which leads to upper airway edema
    • Subglottic stenosis (ie secondary to prolonged intubation or scar formation, typically at the level of the cricoid cartilage)
    • Anaphylactic allergic reactions leading to airway edema
    • Tracheomalacia (weakness of the cartilage leading to floppiness)
    • Laryngomalacia (floppiness of the epiglottis leads to obstruction of the glottis on inspiration, typically omega shaped, affecting infants), "steeple sign"
    • Vocal cord paralysis (ie after cardiac or thyroid surgery)
    • Epiglotttis (decreased incidence with immunization) Previously primarily H influenza, now more commonly group A strep
    • Laryngeal pappilomatosis (ie from being born to a woman with active HPV)
    • Laryngeal tumors or hemangiomas
    • Laryngeal Web
    • Vascular impingement of the trachea (ie inominate artery or vascular rings)
    • Caustic ingestion
    • Burn Injury
    • Angioedema
    • Foreign Body Aspiration
    • Sedation, sleep, medication effect leading to poor upper airway tone 
Figure 3: Laryngomalacia (noted dynamic inspiratory collapse) 

Figure 4: Epiglottitis as seen with laryngoscopy and classic "thumb sign" on lateral neck XR

Figure 5: HPV papillomatosis leading to upper airway obstruction

  • Presentation: 
    • Often marked inspiratory stridor, suggesting extrathoracic airway obstruction
    • Sometimes stertor, or a snoring type noise often indicative of upper airway obstruction from poor pharyngeal tone or obstruction from a large tongue

Treatment

  • Oxygen to support oxygen saturations while working on other interventions
  • Chin lift and jaw thrust maneuvers to attempt to relieve any obstruction from the tongue or poor pharyngeal tone
    Overall goals depending on the underlying etiology:

Reduce Inflammation

  • Steroids: For croup, dexamethasone: 0.6 mg/kg PO X1. For airway edema in the PICU, often dexamethasone 0.25-0.5 mg/kg IV q6 hrs X 4 doses. Mechanism: works as nuclear transcription factor to downregulate inflammation systemically
  • Racemic Epinephrine: Inhaled medication. Mechanism: Alpha-1 agonist that leads to vasoconstriction of inflamed blood vessels, thus leading to reduced edema formation. Temporary bridge while awaiting other therapeutics to work. Has rebound effect typically within 2-3 hours (thus, you can't just give a dose of racemic epinephrine, say things are better, and send a child home/leave their bedside)
Reduce Work of Breathing by Improving Flow/Turbulence

  • Heliox: Mixture of helium and oxygen of various blends: (80% Helium/20% Oxygen, 70% Helium/30% Oxygen, etc.). Helium, due to decreased density, reduces the Reynold's number, thereby helping to promote laminar flow (Reynold's number <2000) instead of turbulent or transitional flow (Reynold's number >4000 and 3000-4000, respectively). There is less airway resistance as a result of this laminar flow and thus, decreased work of breathing. The more helium, the more effective but in some patients, you may be limited in the amount of heliox you can deliver as they may require 50% FiO2 to maintain oxygen saturations. Some clinicians feel that below 60% Helium, there is little to no effect although theoretically, any helium should reduce the Reynold's number and promote improved flow dynamics. Found to improve gas exchange in patients with airway obstruction (Cheifetz 2005)
Stent Open the Area of Obstruction

  • Positive Pressure: CPAP or BiPAP may be used to noninvasively stent open the area of obstruction/collapse
Reduce Work of Breathing by Decreasing Flow Requirement

  • V=IR (Ohm's Law) or Delta pressure (analog of work of breathing) = Flow X Resistance. Flow requirements increase with agitation and thus mild sedation (i.e. dexmedetomidine infusion) can help reduce work of breathing once you've maximized therapy aimed at reducing airway resistance. 

Bypass the Area of Obstruction

  • Nasopharyngeal Tube or Nasal Trumpet: Bypasses potential areas of obstruction such as poor pharyngeal tone (i.e. a patient who received narcotics and is drowsy on the floor) or large tongue. Measured from nares to tragus of the ear. Inserted by using lubrication and inserting directly back towards the posterior aspect of the head. Can be used in awake patient. See Figure below. Contraindicated with CSF leaks/basilar skull fractures



  • Oropharyngeal Tube: Used to assist bag mask ventilation when there may be poor pharyngeal tone or a large tongue leading to obstruction. Cannot be used in awake patients, as it causes them to gag and potentially vomit. Measured from corner of the mouth to the angle of the jaw (mandible) 


  • Endotracheal Tube: Intubation should bypass both any supra and subglottic upper airway extrathoracic obstruction. (It may require a much smaller tube if anatomical obstruction from subglottic stenosis or a hemangioma, etc. exist)

References

1) J.M. Badgwell, M.E. McLeod, J. Friedberg: Airway obstruction in infants and children. Can J Anaesthesia. 34(1):90-98 1987
2) B.D. Kussman, T. Geva, F.X. McGowan: Cardiovascular causes of airway compression. Paediatr Anaesth. 14(1):60-74 2004
3) D.W. Johnson, S. Jacobson, P.C. Edney: A comparison of nebulized budesonide, intramuscular dexamethasone, and placebo for moderately severe croup. N Engl J Med.339 (8):498-503 1998
4) J.E. Weber, C.R. Chudnofsky, J.G. Younger, et al.: A randomized comparison of helium-oxygen mixture (Heliox) and racemic epinephrine for the treatment of moderate to severe croup. Pediatrics. 107 (6):E96 200111389294
5) V.K. Gupta, I.M. Cheifetz: Heliox administration in the pediatric intensive care unit: an evidence-based review.Pediatr Crit Care Med. 6 (2):204-211 2005
6) C.J. Newth, B. Rachman, N. Patel, J. Hammer: The use of cuffed versus uncuffed endotracheal tubes in pediatric intensive care. J Pediatr. 144 (3):333-337 2004