(1191) Effects of Flow Rate During High-Flow Nasal Cannula Use in COVID-19 Respiratory Failure

Introduction: High flow nasal cannula (HFNC) therapy can reduce rates of endotracheal intubation and mortality in COVID-19 patients with respiratory failure when used before mechanical ventilation; however, there is limited information to guide clinicians on the ideal flow-rate settings patients should receive. This study sought to measure the effect of HFNC flow-rates on patient outcomes.

Methods: This was a single-center retrospective review. Adult COVID-19 patients who required HFNC from March 2020 to October 2021 were identified and categorized based on initial HFNC flow-rates: 30-45 or >45 L/minute. Demographics, prognostic risk factors, and clinical outcomes were compared using propensity score matching to pair each >45 L/min flow patient with a corresponding 30-45 L/min flow patient with a similar baseline characteristic set.

Results: Among 910 COVID-19 patients treated with HFNC therapy, 470 required 30-45 L/min flows and 440 required >45 L/min flows. The higher-flow patients had worse severity of illness, including higher sequential organ failure assessment (SOFA) scores (p=0.013) and lower ROX oxygenation indexes (p=0.011). The full set of higher-flow patients had significantly worse 30-day mortality (46.4% versus 38.5% for death) and intubation-free survival (62.0% versus 50.6%) compared to the full set of lower-flow patients. However, after using propensity score matching, essentially no difference exists between the higher-flow patients and their propensity-matched lower-flow patients regarding mortality (42.3% versus 42.6%) or intubation-free survival (59.3% versus 55.1%).

Conclusions: Significant variation exists in the HFNC flow-rates used by different providers, even within a single tertiary referral hospital. Higher flows appear to be used more commonly in patients with worse severity of illness, however the routine use of ultra-high flows (>45 L/min) does not appear to improve clinical outcomes among COVID-19 patients. Although individualizing flow-rates based on clinical findings is necessary, the beneficial physiological effects of HFNC therapy may plateau at excessively high flow-rates and represents a potential source of resource misallocation.