Should infant and pediatric inspiratory flow demand be matched on the high flow nasal cannula (HFNC)?

Matching Infant and Pediatric Inspiratory Flow Demand on HFNC

Yes, you should match infant and pediatric inspiratory flow demand on high-flow nasal cannula, with flow rates of approximately 2 L/kg/min recommended to meet peak inspiratory flow demands and optimize respiratory mechanics. 1, 2

Evidence-Based Flow Rate Recommendations

Initial Flow Rate Selection

• Start with 2 L/kg/min for infants and children up to 10 kg to meet peak inspiratory flow (PIF) demands and achieve optimal therapeutic benefit. 1, 2
• For children above 10 kg, use a minimum of 10 L/min (which approximates 1 L/kg/min for a 10 kg child). 3
• Flow rates below these thresholds (< 1 L/kg/min for patients ≤10 kg or < 10 L/min for patients >10 kg) are considered conventional oxygen therapy, not HFNC. 3

Physiologic Rationale for Matching Flow Demand

• Matching PIF demands at 2 L/kg/min improves respiratory mechanics by reducing airway resistance, decreasing intrinsic positive end-expiratory pressure (PEEP), and increasing tidal volume. 2
• Flow rates set by clinical judgment alone (averaging 1.20-2.05 L/kg/min) successfully met all infants' PIFs in a PICU study, whereas lower rates (1 L/kg/min) were insufficient. 2
• Objective measurements show that 1.5-2.0 L/kg/min produces the largest reduction in work of breathing (measured by pressure-rate product), with a 21% reduction at 2.0 L/kg/min. 4

Weight-Based Considerations

Infants ≤8 kg

• Infants ≤8 kg experience greater benefit from higher flow rates compared to larger children, with more significant reductions in effort of breathing as flows increase from 0.5 to 2.0 L/kg/min. 4
• These smaller infants often present with two distinct phenotypes: normal-PIF infants (PIF <1 L/kg/min) with higher airway resistance, and high-PIF infants (PIF ≥1 L/kg/min) with different respiratory mechanics. 2

Children >8 kg

• Children >8 kg still benefit from flow matching but show less dramatic improvements compared to smaller infants. 4
• Use a minimum of 10 L/min as the threshold for HFNC therapy. 3

Guideline Context and Limitations

Current Guideline Stance

• The 2017 Paediatric Mechanical Ventilation Consensus Conference (PEMVECC) states there is insufficient data to recommend on the use of HFNC in obstructive airway, restrictive, or mixed disease (strong agreement). 3
• Despite this cautious guideline position, HFNC may reduce work of breathing, though outcome data showing superiority over other interventions are lacking. 3

Reconciling Guidelines with Practice

• The PEMVECC guidelines reflect the evidence available through 2015 and acknowledge the lack of high-quality outcome studies. 3
• More recent evidence (2017-2021) demonstrates clear physiologic benefits of matching inspiratory flow demands, even though mortality and morbidity outcomes remain understudied. 2, 4
• The American Academy of Pediatrics recommends HFNC flow rates of at least 2 L/kg/min for optimal therapeutic effect. 1

Practical Implementation Algorithm

Step 1: Initial Setup

• Calculate weight-based flow: 2 L/kg/min for infants ≤10 kg. 1, 2
• For a 5 kg infant: start at 10 L/min. 1
• For a 12 kg child: start at 12-24 L/min (1-2 L/kg/min range). 5

Step 2: Titration Based on Response

• Monitor respiratory rate (should decrease with effective therapy), work of breathing (reduced accessory muscle use, retractions), and oxygen saturation (target SpO2 ≥94-95%). 1, 5
• If respiratory distress persists after 1-2 hours, increase flow in 5-10 L/min increments before escalating FiO2. 1, 5

Step 3: FiO2 Adjustment

• Start with FiO2 30-40% and titrate in 5-10% increments to maintain SpO2 94-98%. 1, 5
• Avoid hyperoxia (SpO2 100%) as this may mask inadequate ventilation. 5

Common Pitfalls to Avoid

Insufficient Flow Rates

• Using 1 L/kg/min is inadequate for most infants as it fails to meet PIF demands and provides suboptimal reduction in work of breathing. 2, 4
• Clinical judgment alone without weight-based calculations may result in underestimation of required flow. 2

Delayed Recognition of Failure

• HFNC should not delay intubation when clinically indicated. 5, 6
• Escalate to higher support if respiratory rate remains >50 breaths/min after 1-2 hours or if FiO2 requirement reaches ≥50%. 1

Inadequate Monitoring

• HFNC lacks continuous pressure monitoring, creating risk for pressure-dependent complications including pneumothorax (reported in 17.9% of German pediatric clinics). 7
• Use HFNC only in settings with continuous cardiorespiratory monitoring capabilities. 1, 7

Equipment and Humidification Issues

• Humidification is mandatory to prevent mucosal drying and secretion thickening. 5, 6
• Ensure proper nasal cannula sizing (should not occlude >50% of nares) to avoid excessive pressure buildup. 6

Special Clinical Scenarios

Post-Extubation Support

• For children at high risk of extubation failure, use noninvasive respiratory support (HFNC, CPAP, or NIV) over conventional oxygen therapy immediately after extubation. 3
• For children <1 year being started on noninvasive respiratory support, CPAP is preferred over HFNC (conditional recommendation, low certainty). 3

Bronchiolitis

• HFNC at 2 L/kg/min is particularly effective in moderate-to-severe bronchiolitis, reducing work of breathing and improving respiratory mechanics. 2, 6
• Most pediatric literature supports HFNC benefits specifically for this indication. 6