Rittayamai N, et al. - In this preliminary prospective physiologic study, researchers focused on the physiologic influences of high-flow nasal cannula (HFNC) at various flow rates in 12 hypercapnic chronic obstructive pulmonary disease (COPD) patients who had initially needed non-invasive ventilation (NIV), and were ventilated with HFNC at flow rates rising from 10 to 50 L/min for 15 min in each step. They also compared it with NIV. The struggle to breathe determined by a simplified esophageal pressure–time product was the primary outcome. Respiratory rate, oxygen saturation, and transcutaneous CO₂ pressure were also evaluated. Findings revealed reduced inspiratory effort in correlation with the application of HFNC at 30 L/min for a short duration vs 10 and 20 L/min. In hypercapnic COPD with mild to moderate exacerbation, a similar effect was produced when HFNC was applied at 30 L/min for a short duration vs NIV delivered at modest levels of pressure support. A fall in respiratory rate but sometimes an increase in the effort to breathe was induced by higher flow rates. Experts recommended further evaluation of the use of HFNC at 30 L/min in hypercapnic COPD patients.