Residency · Residency · Internal Medicine
Non-Invasive Ventilation and High-Flow Nasal Cannula
Introduction
Non-invasive ventilation (NIV) and high-flow nasal cannula (HFNC) are respiratory support modalities that can prevent intubation, reduce complications of invasive mechanical ventilation, and improve patient outcomes when applied to the right clinical scenario. Understanding the mechanisms, indications, contraindications, and evidence for each modality is essential for internal medicine residents managing acute respiratory failure.
Mechanisms of Action
Non-Invasive Positive Pressure Ventilation (NIPPV)
- Delivers positive airway pressure via a tight-fitting mask (oronasal, full-face, or helmet interface)
- BiPAP (bilevel positive airway pressure): inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP)
- IPAP provides ventilatory support (augments tidal volume, reduces work of breathing)
- EPAP provides PEEP (recruits alveoli, improves oxygenation, counteracts auto-PEEP)
- Pressure support = IPAP minus EPAP
- CPAP (continuous positive airway pressure): single level of pressure throughout the respiratory cycle; does not augment ventilation
- Key physiologic effects: reduces preload and afterload (beneficial in cardiogenic pulmonary edema), splints airways open, improves FRC
High-Flow Nasal Cannula (HFNC)
- Delivers heated, humidified oxygen at flow rates of 30-60 L/min via wide-bore nasal prongs
- Mechanisms of benefit:
- Matches or exceeds patient inspiratory flow demand, reducing entrainment of room air and providing reliable FiO2
- Generates modest PEEP (approximately 1 cmH2O per 10 L/min of flow with mouth closed)
- Nasopharyngeal dead space washout: reduces CO2 rebreathing, improving ventilatory efficiency
- Superior comfort and humidification compared to conventional oxygen and NIV
- Reduces respiratory rate and work of breathing
Indications and Evidence
| Clinical Scenario | Preferred Modality | Strength of Evidence | Key Trial |
|---|---|---|---|
| COPD exacerbation (hypercapnic) | BiPAP | Strong | Brochard 1995, Plant 2000 |
| Cardiogenic pulmonary edema | CPAP or BiPAP | Strong | 3CPO trial |
| De novo hypoxemic respiratory failure | HFNC | Moderate-Strong | FLORALI trial |
| Post-extubation (high-risk) | NIV | Moderate | Ferrer 2006 |
| Post-extubation (low-risk) | HFNC | Moderate | Hernandez 2016 |
| DNI patient (ceiling of care) | HFNC or NIV | Expert consensus | N/A |
COPD Exacerbation (NIV -- STRONG Indication)
- NIV (BiPAP) is the standard of care for acute hypercapnic respiratory failure in COPD
- Reduces intubation rate (NNT = 5), ICU length of stay, and in-hospital mortality (NNT = 8)
- Typical settings: IPAP 10-20 cmH2O, EPAP 4-8 cmH2O, titrate to respiratory rate and comfort
- ABG after 1-2 hours: if pH worsening or no improvement, consider intubation
- Landmark evidence: Brochard 1995, Plant 2000, Cochrane meta-analysis
Acute Cardiogenic Pulmonary Edema (NIV -- STRONG Indication)
- CPAP or BiPAP reduces intubation rate and improves symptoms more rapidly than standard oxygen
- CPAP at 10-12 cmH2O is effective; BiPAP may provide additional benefit in severe cases with hypercapnia
- 3CPO trial: NIV reduced dyspnea and metabolic derangements faster than standard oxygen; no mortality difference
- Mechanism: positive pressure reduces preload (decreased venous return) and afterload (reduced transmural LV pressure), improving cardiac output
Acute Hypoxemic Respiratory Failure (HFNC vs. NIV -- Nuanced)
- FLORALI trial: HFNC (Optiflow at 50 L/min) reduced 90-day mortality and intubation rates compared to standard oxygen and NIV in non-hypercapnic hypoxemic respiratory failure (P/F < 200 subgroup)
- HFNC is increasingly preferred over NIV for de novo hypoxemic respiratory failure (pneumonia, ARDS) because:
- NIV may generate harmful large tidal volumes that worsen lung injury (patient self-inflicted lung injury)
- HFNC provides better patient comfort and tolerability
- COVID-19 experience: HFNC with prone positioning reduced intubation rates in moderate-severe hypoxemia
Post-Extubation Respiratory Support
- High-risk patients (age > 65, cardiac or respiratory comorbidities): NIV for 24-48 hours post-extubation reduces reintubation (Ferrer 2006, Nava 2005)
- Low-risk patients: HFNC non-inferior to NIV in preventing reintubation (Hernandez 2016)
- HFNC is preferred for routine post-extubation support due to comfort and tolerability
Other Indications
- Obesity hypoventilation syndrome: NIV (BiPAP) for acute decompensation
- Neuromuscular respiratory failure: NIV to support ventilation (ALS, myasthenia crisis)
- Do-not-intubate (DNI) patients: NIV or HFNC as ceiling of respiratory support
- Pre-oxygenation for intubation: HFNC during apneic period maintains oxygenation; NIV for pre-oxygenation in obese patients
Contraindications to NIV
- Absolute: cardiac or respiratory arrest, inability to protect airway, facial trauma/burns/surgery precluding mask fit, uncooperative or obtunded patient (GCS < 10), copious secretions with impaired clearance
- Relative: hemodynamic instability, severe hypoxemia (P/F < 100), high aspiration risk, recent upper GI or esophageal surgery
Interface Selection for NIV
- Oronasal mask: most commonly used; effective for acute respiratory failure
- Full-face mask: covers entire face; reduces air leak but claustrophobia risk
- Helmet interface: eliminates facial pressure points; shown to reduce intubation in ARDS (Patel 2016); may reduce aerosol dispersion; requires higher PEEP settings
- Proper mask fit is critical: air leak reduces efficacy and causes facial skin breakdown
Monitoring and Failure Recognition
Signs of NIV/HFNC Success (Reassess at 1-2 Hours)
- Decreasing respiratory rate (target < 25/min)
- Improving oxygen saturation and PaO2/FiO2 ratio
- Decreasing accessory muscle use
- Improving mental status and patient comfort
- Improving pH and PaCO2 on ABG (for hypercapnic failure)
Signs of Failure -- Proceed to Intubation
- Persistent or worsening tachypnea (RR > 35)
- Hemodynamic instability
- Worsening hypoxemia despite maximal settings
- Inability to handle secretions or protect airway
- Patient agitation or encephalopathy
- ROX index for HFNC: (SpO2/FiO2) / RR; ROX < 3.85 at 12 hours predicts HFNC failure and need for intubation
Key Clinical Pearls
- NIV for COPD exacerbation and cardiogenic pulmonary edema has the strongest evidence and should be initiated early before clinical deterioration
- HFNC is preferred over NIV for de novo hypoxemic respiratory failure (pneumonia, ARDS) to avoid patient self-inflicted lung injury from excessive tidal volumes
- Delayed intubation due to prolonged NIV or HFNC trial in a failing patient increases mortality; reassess within 1-2 hours and have a low threshold for intubation
- The ROX index (SpO2/FiO2 divided by respiratory rate) is a validated tool for predicting HFNC failure
References
- Rochwerg B, Brochard L, Elliott MW, et al. Official ERS/ATS Clinical Practice Guidelines: Noninvasive Ventilation for Acute Respiratory Failure. Eur Respir J. 2017;50(2):1602426.
- Frat JP, Thille AW, Mercat A, et al. High-Flow Oxygen through Nasal Cannula in Acute Hypoxemic Respiratory Failure (FLORALI). N Engl J Med. 2015;372(23):2185-2196.
- Gray A, Goodacre S, Newby DE, et al. Noninvasive Ventilation in Acute Cardiogenic Pulmonary Edema (3CPO). N Engl J Med. 2008;359(2):142-151.
- Roca O, Caralt B, Messika J, et al. An Index Combining Respiratory Rate and Oxygenation to Predict Outcome of Nasal High-Flow Therapy (ROX Index). Am J Respir Crit Care Med. 2019;199(11):1368-1376.