Today’s case presentation involves a 2-year-old girl who was previously healthy and was admitted to the Pediatric Intensive Care Unit (PICU) for acute respiratory distress characterized by increased work of breathing and wheezing.

Case Presentation

A 2-year-old girl with acute respiratory distress due to RSV infection

  • Presented with increased work of breathing, wheezing, and no fever
  • Started on High Flow Nasal Cannula (HFNC) therapy in the PICU

Key Elements:

  • Prodrome of URI symptoms
  • Increased respiratory effort (nasal flaring, intercostal retractions, decreased lung base air entry)
  • HFNC improved the work of breathing and oxygen saturation

Physiology of HFNC

Mechanisms of Action

Washout of Nasopharyngeal Dead Space:

  • HFNC clears nasopharyngeal dead space, improving oxygen efficiency.
  • Reduces re-breathing of CO2 from the anatomical dead space.
  • Enhances ventilation efficiency and oxygenation.

Reduction in Upper Airway Resistance:

  • HFNC reduces resistance in the upper airway.
  • Delivers rapid gas flow matching or exceeding natural inhalation rate.
  • Eases breathing, especially in neonates and infants with narrow airways.

Optimal Conditioning of Gas:

  • HFNC delivers heated and humidified oxygen, matching the body’s conditions.
  • Reduces energy expenditure and risk of airway irritation
  • More comfortable and effective compared to cold, dry air delivery

Debunking the PEEP Theory (Positive End-Expiratory Pressure) 

  • HFNC generates minimal and variable PEEP.
  • Amount of PEEP depends on factors like flow rate and cannula size
  • Not as high or consistent as other respiratory support devices

Research Findings

  • A 2022 CHEST study by Khemani et al. on children with bronchiolitis challenged the conventional understanding of HFNC’s mechanisms.
  • HFNC primarily reduces breathing effort but does not consistently increase lung volume (EELV) or tidal volume (VT).
  • Reduction in the pressure rate product (PRP) indicates decreased breathing effort, but not significant alterations in EELV or VT.

Physiological Effects

  • HR, RR, and SpO2 are key indicators of HFNC efficacy.
  • HR and RR should approach normal ranges for the child’s age.
  • Improvement in SpO2 levels while maintaining or reducing FiO2 indicates a positive response.


  • HFNC is a valuable tool in pediatric care for alleviating respiratory distress.
  • Not a one-size-fits-all solution; vigilant monitoring and reassessment are crucial
  • Recognizing HFNC’s mechanisms allows for optimized bedside application.

Closing Remarks:

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