High flow nasal cannula improves breathing efficiency and ventilatory ratio in COPD patients recovering from an exacerbation.

Abstract

High flow nasal cannula (HFNC) may improve CO2 elimination by washing out CO2 from the upper airways. This study aimed at assessing the effect of HFNC on minute ventilation and ventilatory ratio (VR), a surrogate of dead space, in patients hospitalized for acute hypercapnic COPD exacerbation. Physiological study comparing HFNC at 40 L/min to low flow oxygen. Variations of tidal volume (VT) and minute ventilation between the two treatments were estimated from chest plethysmography. Respiratory rate (RR) and arterial blood gases were measured. Variations in VR were calculated. Data were compared using Wilcoxon tests. Recordings performed in 10 patients. Minute ventilation was reduced with HFNC by -16.2 [-30.9-0.4] % (p = 0.049). VT was not different but RR was lower during HFNC. PaCO2 was lower with HFNC compared to standard oxygen: 48.7 [46.4-58.1] vs 50.7 [48.4-57.5] mmHg (p = 0.020). VR decreased by -18.0 [-34.7 - -4.0] % (p = 0.020) with HFNC. In patients recovering from acute COPD exacerbation, the use of HFNC reduced RR, minute ventilation, PaCO2 and VR compared to standard oxygen. These changes are consistent with a decrease in physiologic dead space with HFNC.