Effectiveness of nasal highflow in hypercapnic COPD patients is flow and leakage dependent

Nasal Highflow (NHF) delivers a humidified and heated airflow via nasal prongs. Current data provide evidence for efficacy of NHF in patients with hypoxemic respiratory failure. Preliminary data suggest that NHF may decrease hypercapnia in hypercapnic respiratory failure. The aim of this study was to evaluate the mechanism of NHF mediated PCO reduction in patients with chronic obstructive pulmonary disease (COPD). In 36 hypercapnic COPD patients (PCO > 45 mmHg), hypercapnia was evaluated by capillary gas sampling 1 h after NHF breathing under four conditions A to D with different flow rates and different degrees of leakage (A = 20 L/min, low leakage, two prongs, both inside; B = 40 L/min, low leakage, two prongs, both inside; C = 40 L/min, high leakage, two prongs, one outside and open; D = 40 L/min, high leakage, two prongs, one outside and closed). Under identical conditions, mean airway pressure was measured in the hypopharynx of 10 COPD patients. Hypercapnia significantly decreased in all patients. In patients with capillary PCO > 55 mmHg (n = 26), PCO additionally decreased significantly by increased leakage and/or flow rate in comparison to lower leakage/ flow rate conditions (A = 94.2 ± 8.2%; B = 93.5 ± 4.4%; C = 90.5 ± 7.2%; D = 86.8 ± 3.8%). The highest mean airway pressure was observed in patients breathing under condition B (2.3 ± 1.6 mbar; p