- In pts with anoxic brain injury after cardiac arrest, severe stroke – O2 has a U-shaped mortality curve. Don’t get supra-therapeutic PaO2.
- NEJM 6/4/15: High-flow O2 was superior to BiPAP and NC for hypoxic patients – improved mortality with decreased need for procedures and intervention.
High-Flow Oxygen for Respiratory Support
Trials support using HFO in selected patients with acute hypoxemic respiratory failure and in patients with postoperative hypoxemia.
Multiple trials support using noninvasive positive pressure ventilation (NPPV) in patients with chronic obstructive pulmonary disease exacerbations and cardiogenic pulmonary edema. NPPV is most effective in rapidly reversible conditions where supporting the work of breathing can allow pharmacologic interventions to take effect. Whether NPPV is beneficial in treating patients with hypoxemic respiratory failure (i.e., respiratory failure not secondary to conditions causing hypercarbia) is unclear. High-flow oxygen (HFO) generators are a relatively new addition to the spectrum of respiratory support. These set-ups allow for comfortable delivery of very high flows of oxygen (e.g., 60 L per minute). Flows are high enough to achieve low levels of positive end expiratory pressure (PEEP) and potentially to recruit atelectatic alveoli. HFO delivered by nasal cannula might be an alternative to NPPV in patients with hypoxemia as the predominant feature of their respiratory failure. Investigators explored these alternatives in two multicenter European studies.
In one trial, 310 patients with hypoxemic respiratory failure (>60% with community-acquired pneumonia; none with hypercarbia) were randomized to HFO, NPPV, or standard oxygen delivery. Criteria for intubation included relatively conservative thresholds for pH (<7.35) and oxygen saturation (<90% for >5 minutes). Intubation rates did not differ significantly among the three groups but tended to be lower in the HFO group. The HFO group also had significantly lower 90-day mortality, more ventilator-free days, and less respiratory discomfort (NEJM JW Gen Med Aug 1 2015 and N Engl J Med 2015; 372:2185). In the other randomized trial, researchers compared NPPV with HFO in 830 patients with hypoxemia after cardiothoracic surgery. Reintubation rates and intensive care unit mortality were similar in the two groups (NEJM JW Gen Med Aug 1 2015 and JAMA 2015; 313:2331).
These results support using HFO in selected patients with acute hypoxemic respiratory failure and in patients with postoperative hypoxemia. Using HFO as first-line therapy in these patients makes sense, but we should note that all patients with elevated carbon dioxide levels were excluded from both studies. Ventilatory support (i.e., NPPV) remains the preferred treatment in patients with hypercarbic respiratory failure due to chronic obstructive pulmonary disease. This distinction in gas exchange abnormality (i.e., presence or absence of hypercarbia in hypoxemic patients) is essential in treatment decision-making.
- HFO2 can delivery up to 60L/min with ranges up to 100% FiO2. Also, it provides anywhere from 3-8 cmH2O of CPAP!
- For each 1L/min on NC, increase in FiO2 is roughly 2-4% (but it varies patient to patient based on dead space, mucosal absorption, etc.)
- Not indicated (and not studied) in COPDers – that’s a ventilatory problem > oxygenation.
Article demonstrating success of HFO2 vs invasive methods in hypoxic respiratory failure, from NEJM.