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
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