Physiology: Comparison of BiPAP vs HFNC in pneumonia
- Oxygenation: Both devices can provide close to 100% FiO2. HFNC can provide a small and variable amount of PEEP (perhaps ~5cm, depending on the flow rate and how snugly the nasal prongs fit into the patient's nose). BiPAP can provide a greater amount of PEEP in a more precise fashion.
- Work of Breathing: HFNC may wash out the anatomic deadspace, thereby reducing the work of breathing (explained previously here). BiPAP can provide higher inspiratory pressures, and at high settings may provide the majority of the work of breathing.
- Secretion clearance: This is essential in the setting of pneumonia to prevent mucus plugging and remove purulent material from the lungs. BiPAP typically impairs secretion tolerance, whereas HFNC does not seem to.
- Monitoring: BiPAP can impair patient monitoring by interfering with speech and observation of facial expressions. Additionally, when patients get anxious on BiPAP, it can be confusing to tell whether this is claustrophobia from the mask or respiratory exhaustion. HFNC facilitates communication and early detection of patients who are failing and require intubation.
Evidence before FLORALI
Confalonieri et al. 1999 American Journal of Respiratory and Critical Care Medicine
Ferrer et al. 2003 American Journal of Respiratory and Critical Care Medicine
Summary of prior evidence
FLORALI study (Frat et al. NEJM 2015)
- FLORALI is a large RCT directly comparing HFNC vs. BiPAP vs. non-rebreather facemask for patients with hypoxemic respiratory failure (82% with pneumonia). Until now there has been very little evidence about this.
- HFNC caused a reduction in mortality and days spent on invasive mechanical ventilation. This supports the use of HFNC as the first-line approach to noninvasive support of patients with pneumonia.
- In order to provide optimal support for the work of breathing, HFNC should probably be set at a high flow rate (i.e. 50 liters/minute flow) if tolerated.
- Use of BiPAP was associated with trends towards increased intubation rate and higher mortality. This might be due to BiPAP interfering with expectoration of secretions, leading to mucus plugging.
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