Reduction of PaCO2 by high-flow nasal cannula in acute hypercapnic respiratory failure patients receiving conventional oxygen therapy

Background: It has been suggested that a high-flow nasal cannula (HFNC) could help to remove carbon dioxide (CO2) from anatomical dead spaces, but evidence to support that is lacking. The objective of this study was to elucidate whether use of an HFNC could reduce the arterial partial pressure of CO2 (PaCO2) in patients with acute hypercapnic respiratory failure who are receiving conventional oxygen (O-2) therapy. Methods: A propensity score-matched observational study was conducted to evaluate patients treated with an HFNC for acute hypercapnic respiratory failure from 2015 to 2016. The hypercapnia group was defined as patients with a PaCO2 > 50 mm Hg and arterial pH < 7.35. Results: Eighteen patients in the hypercapnia group and 177 patients in the nonhypercapnia group were eligible for the present study. Eighteen patients in each group were matched by propensity score. Decreased PaCO2 and consequent pH normalization over time occurred in the hypercapnia group (P=0.002 and P=0.005, respectively). The initial PaCO2 level correlated linearly with PaCO2 removal after the use of an HFNC (R-2=0.378, P=0.010). The fraction of inspired O-2 used in the intensive care unit was consistently higher for 48 hours in the nonhypercapnia group. Physiological parameters such as respiratory rate and arterial partial pressure of O-2 improved over time in both groups. Conclusions: Physiological parameters can improve after the use of an HFNC in patients with acute hypercapnic respiratory failure given low-flow O-2 therapy via a facial mask. Further studies are needed to identify which hypercapnic patients might benefit from an HFNC.