Pulmonary · Topic 4 of 28

Noninvasive Ventilation & High-Flow Nasal Cannula

Pulmonary · noninvasive respiratory support

Noninvasive Ventilation & High-Flow Nasal Cannula

BiPAP for hypercapnic COPD with pH ≤ 7.35 and for cardiogenic pulmonary edema; high-flow nasal cannula for hypoxemic failure — reassess within 1–2 hours.

Key numbers

BiPAP for COPD with pH ≤ 7.35pH ≤ 7.35

Reassess within 1–2 hours; intubate if worsereassess at 1–2 h

ROX ≥ 4.88 predicts high-flow successROX ≥ 4.88

01 · The ruleBiPAP for COPD with pH ≤ 7.35

Bilevel NIV is strongly recommended for COPD exacerbation with acute or acute-on-chronic respiratory acidosis — pH ≤ 7.35, PaCO₂ > 45 mmHg, RR > 20–24 despite medical therapy; it cuts intubation and mortality.

02 · The ruleCPAP or BiPAP for cardiogenic pulmonary edema

CPAP or bilevel NIV is strongly recommended for respiratory failure from cardiogenic pulmonary edema — it lowers intubation and mortality; patients in cardiogenic shock were excluded from the trials.

03 · WatchReassess within 1–2 hours; intubate if worse

Responders improve within the first 1–4 hours (usually 1–2): falling respiratory rate and rising pH predict success; no improvement means prompt intubation, because delayed intubation raises mortality.

What it is

Core idea

Raise IPAP for CO₂, EPAP for oxygenEPAP is the equivalent of PEEP and improves oxygenation by holding alveoli open; IPAP adds inspiratory support that raises tidal volume, so widening the IPAP–EPAP gap clears more CO₂.

High-flow washes out dead spaceHigh-flow nasal cannula delivers heated, humidified gas that washes out anatomic dead space, gives a steadier FiO₂ and adds 3–5 cmH₂O of positive pressure with the mouth closed; it is better tolerated than a mask.

Diagnosis & monitoring

Work-up

ROX ≥ 4.88 predicts high-flow successROX index = (SpO₂/FiO₂) ÷ respiratory rate; ≥ 4.88 at 2, 6 or 12 hours predicts high-flow success, while < 2.85, < 3.47 or < 3.85 at those times predicts failure and need for intubation.

Do right now

In this order

First moves

No NIV: arrest, obtunded, vomiting, airway at risk

→

Start BiPAP at IPAP 10–12, EPAP 5–7

→

Reassess within 1–2 hours; intubate if worsereassess at 1–2 h

Why each step

No NIV: arrest, obtunded, vomiting, airway at riskDo not use NIV in cardiac or respiratory arrest (or impending), obtundation or inability to cooperate, copious secretions, vomiting or upper GI bleeding, facial trauma, upper airway obstruction, or hemodynamic instability.

Start BiPAP at IPAP 10–12, EPAP 5–7Typical starting BiPAP: IPAP 10–12 and EPAP 5–7 cmH₂O; reassess from 30 minutes and raise IPAP as needed to a maximum of 20 cmH₂O (esophageal opening pressure) to avoid gastric insufflation.

Reassess within 1–2 hours; intubate if worseResponders improve within the first 1–4 hours (usually 1–2): falling respiratory rate and rising pH predict success; no improvement means prompt intubation, because delayed intubation raises mortality.

Management

Orders

Start high-flow at 40 L/min, FiO₂ 100%Start high-flow nasal cannula at FiO₂ 100% and 40 L/min, raise flow up to 60 L/min to ease respiratory rate and work of breathing, then wean FiO₂ to the target saturation.

Intubate for shock, arrhythmia, falling alertnessConvert to intubation for shock, frequent arrhythmias, myocardial ischemia, decreasing alertness, persistent high work of breathing, or transfer to the cath lab or OR where airway control is needed.

The rules

Know these

High-flow cannula for hypoxemic failure must knowFor acute hypoxemic respiratory failure, high-flow nasal cannula is suggested over conventional oxygen and over NIV (ERS 2022, conditional); it may prevent intubation when P/F is below 200.

Caution with NIV in de novo hypoxemiaNIV for de novo hypoxemic failure (pneumonia, ARDS) has no guideline recommendation: large tidal volumes may injure the lung and failure delays intubation; use only in selected patients in the ICU with early reassessment.

No NIV for hypercapnia without acidosisIn a COPD exacerbation with hypercapnia but a normal pH, NIV is suggested against; treat medically with oxygen titrated to SpO₂ 88–92%.

Post-extubation: prevent in high risk, not rescueUse NIV right after extubation to prevent failure in high-risk patients (age > 65, cardiac or respiratory disease, hypercapnia), but not to treat established post-extubation failure — that delays reintubation and raised mortality.

Hypercapnic COPD: trial NIV before high-flowIn COPD with hypercapnic failure, try NIV before high-flow nasal cannula; high-flow can be used when the mask is not tolerated or during breaks from NIV.

NIV also helps post-op, immunocompromised, DNINIV is also suggested for postoperative respiratory failure, immunocompromised patients, chest trauma once pain is controlled, weaning hypercapnic patients, and palliation of dyspnea in terminal illness.

BiPAP or high-flow nasal cannula?

Commonly confused

Strongest evidence	Hypercapnic COPD (pH ≤ 7.35); cardiogenic pulmonary edema
How it helps	IPAP raises tidal volume; EPAP acts as PEEP
Pressure delivered	IPAP above EPAP; IPAP no higher than 20 cmH₂O
Starting settings	IPAP 10–12, EPAP 5–7 cmH₂O
In hypercapnic COPD	First choice

More detail

Reference

Show 4 reference facts

NIV complications include aspiration into the unprotected airway, barotrauma (including tension pneumothorax) and gastric insufflation when IPAP exceeds about 20 cmH₂O.

There is no pH floor below which an NIV trial in COPD is wrong, but the lower the pH the higher the failure risk, so very acidotic patients need ICU-level monitoring with intubation ready.

No guideline recommendation exists for NIV in acute asthma; if tried in status asthmaticus, introduce low CPAP (3–5 cmH₂O) first and avoid it when intubation is imminent.

A helmet interface is better tolerated than a face mask over long periods; outpatient CPAP treats obstructive sleep apnea, and BiPAP treats obesity hypoventilation and chronic neuromuscular or chest-wall failure.

Pearl

Noninvasive support buys time, never at the cost of a late intubation: no better in 1–2 hours means intubate.

Sources · Rochwerg B et al. Official ERS/ATS clinical practice guidelines: noninvasive ventilation for acute respiratory failure. Eur Respir J 2017;50:1602426 · Merck Manual Professional — Acute Hypoxemic Respiratory Failure (AHRF), Including ARDS · Merck Manual Professional — How To Do Noninvasive Positive Pressure Ventilation · Merck Manual Professional — Noninvasive Positive Pressure Ventilation (NIPPV) and high-flow nasal oxygen · Oczkowski S et al. ERS clinical practice guidelines: high-flow nasal cannula in acute respiratory failure. Eur Respir J 2022;59:2101574 · Merck Manual Professional — Ventilatory Failure · Roca O et al. An index combining respiratory rate and oxygenation to predict outcome of nasal high-flow therapy. Am J Respir Crit Care Med 2019;199:1368–1376 · Merck Manual Professional — Treatment of Acute COPD Exacerbation · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).