Literature Summary

Major Literature

HFNC

Basics:

• HFNC is generally well tolerated

• Flow ranges from 1-40L/min

• Gas can be humidified and warmed

• Decreases WOB and CO2

• Increases O2 sat

Proposed Mechanism of Action:

• Washes out CO2 rich gas from anatomical dead space (areas that are ventilated but not perfused, such as the area between the mouth to bronchi)

• Provides positive airway pressure to stent open airways and decreases inspiratory effort

• Since HFNC air is warmed and humidified, the body expends less energy optimizing the gas

2012 - Predictors of Failure in Infants with Viral Bronchiolitis Treated with HFNC (Peds Critical Care Med)

• Methods

  • Retrospective study done in Ohio (booo)

  • Inclusion

    • = or <12 months of age requiring HFNC for viral bronchiolitis in the PICU

  • HFNC 3-8L/min used to maintain O2 sat >92%

  • Compared responders (avoided intubation) vs. non-responders (got intubated) to HFNC

• Results/Discussion

  • 113 pts met criteria

    • 19% failed, 81% succeeded

  • General

    • Non-responders were intubated by ~14 hrs in avg

    • Non-responders had significantly lower pH (7.26 vs. 7.30) and higher PCO2 (67 vs. 56) prior to initiation of HFNC

    • Non-responders had significantly lower RR (44 vs. 54) prior to initiation of HFNC

  • Pre HFNC to 1 hr post HFNC

    • Non-responders had no change in RR pre/post HFNC while responders had a decrease of ~8 in their RR

    • Responders had decreased episodes of desats while non-responders were likely to have persistent desats

  • Most likely predictors of not responding to HFNC:

    • High PCO2 = poor ventilation

    • Low RR = less tachypnea = pts getting fatigued and could no longer increase their min ventilation

2013 - Is HFNC Effective in Acute Viral Bronchiolitis? (Intensive Care Med)

• Methods

  • Prospective study done in France

  • Inclusion

    • <6 months of age with RSV bronchiolitis requiring HFNC in the PICU

  • Measured pharyngeal pressure (estimate of PEEP) at different flow rates

• Results/Discussion

  • 21 pts met criteria

  • Flows = or >6L/min generated positive pressure during both inspiration and expiration

  • Flows = or >2L/kg/min associated w/ pharyngeal pressure = or >4cmH2O

  • Increasing from 1 to 7L/min resulted in significant reduction in RR and 50% reduction in WOB score

  • No complications from HFNC use

  • None of the 21 pts required intubation

  • To maximize benefit from HFNC, put pacifier in pt's mouth and use largest prongs that fit into nostrils (minimize positive pressure leaks)

2014 - Effort of Breathing in Children Receiving HFNC (Peds Critical Care Med)

• Methods

  • Prospective study done in California

  • Inclusion

    • <18 yrs of age receiving HFNC or pts planned to extubate to HFNC w/in 72hrs (mean age of this cohort ~7 yrs)

  • Esophageal pressure (estimate of pleural pressure; negative pressure in the pleural = chest expands (inhalation) because the lung gets pulled against the chest wall; positive pressure = expiration because the lung gets pushed away from the chest wall) measured during CPAP 4-5 and HFNC 2-8L/min

  • WOB, determined by PRP (pressure rate product; change in pleural pressure X RR; lower number means less WOB), calculated for CPAP and HFNC

• Results/Discussion

  • 25 pts met criteria (20 pts initially intubated)

    • PRP collected on HFNC for 25 pts, CPAP for 18 pts, and NC for 20 pts

  • PRP significantly lower on HFNC 8L/min vs. HFNC 2-5L/min (even significantly different at HFNC 5L/min vs. HFNC 2L/min)

  • PRP of CPAP not significantly different from HFNC 5-8L/min but significantly lower compared to HFNC 2L/min

  • PRP decreased by 25% when flow rate of HFNC increased from 2 to 8L/min

  • Esophageal pressure at end exhalation (estimate of PEEP) increased when flow rate of HFNC increased from 2L/min to 8L/min

    • No significant difference in esophageal pressure at end exhalation between CPAP and HFNC 8L/min but significantly different with HFNC 2-5L/min

  • No adverse events with HFNC