HFNC is the first-line non-invasive support for acute hypoxaemic respiratory failure. Start at 50-60 L/min, titrate FiO2 to target, and use the ROX index at 2, 6 and 12 h to avoid delayed intubation.
At the bedside
Timed steps- 1
Acute hypoxaemic respiratory failure
IndicationSpO2 < 92% on ≥ 6-10 L/min, RR > 25-30, increased work of breathing, not hypercapnic. Also post-extubation in low-to-moderate risk patients and for preoxygenation.
- 2
Settings
StartFlow 50-60 L/min (start 40 if not tolerated), FiO2 to SpO2 92-96%, temperature 37 °C (31-34 if uncomfortable). Largest prongs that fit (≤ 50% of nostril).
- 3
ROX index
MonitorROX = (SpO2/FiO2) ÷ RR. At 2, 6 and 12 h: ≥ 4.88 predicts success. < 2.85 at 2 h, < 3.47 at 6 h or < 3.85 at 12 h predicts failure.
- 4
Do not delay intubation
EscalatePersisting high RR, thoraco-abdominal asynchrony, FiO2 > 0.7-0.8, falling ROX: intubate in a controlled way.
- 5
When better
WeanReduce FiO2 first to ≤ 0.4, then flow in 5-10 L/min steps to 20-30 L/min, then switch to conventional oxygen.
ROX index interpretation
| Time on HFNC | Likely success | Likely failure (consider intubation) |
|---|---|---|
| 2 h | ≥ 4.88 | < 2.85 |
| 6 h | ≥ 4.88 | < 3.47 |
| 12 h | ≥ 4.88 | < 3.85 |
Values in between are indeterminate: reassess in 1-2 h.
Calculators for this topic
References
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HFNC monitoring
Step 1 of ~3
Decision: Hypercapnic acidosis (pH < 7.35, PaCO2 > 45)?
Based on Roca O, Caralt B, Messika J, et al; Grasselli G, Calfee CS, Camporota L, et al. Educational use; follow local protocol.
Evidence
- FLORALI (2015): HFNC vs standard oxygen vs NIV in non-hypercapnic AHRF: intubation rates did not differ significantly overall (38%, 47%, 50%) but were lower with HFNC in P/F ≤ 200; 90-day mortality was lower with HFNC.
- ROX (2019): validated thresholds at 2, 6 and 12 h.
- ESICM 2023: recommends HFNO over conventional oxygen to reduce intubation in AHRF (not due to COVID); no recommendation for or against NIV vs HFNO in non-COVID AHRF.
- Hernández 2016: HFNC was non-inferior to NIV for preventing reintubation in high-risk patients.
Controversies
- Helmet NIV vs HFNC in severe hypoxaemia; awake proning outside COVID-19.
🇮🇳 India notes
- HFNC devices (including lower-cost Indian-made units) are now widespread but need a high-flow oxygen supply (up to 60 L/min); calculate cylinder or manifold capacity, especially in smaller hospitals.
References
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