High-flow nasal cannula may prolong the length of hospital stay in patients with hypercapnic acute COPD exacerbation

Background: High-flow nasal cannula (HFNC) is increasingly used in patients with acute exacerbation of COPD (AECOPD). We aimed to confirm whether the baseline bicarbonate is an independent predictor of outcomes in patients with hypercapnic AECOPD receiving HFNC. Methods: This was a secondary analysis of a multicentre randomised trial that enrolled 330 patients with non-acidotic hypercapnic AECOPD supported by HFNC or conventional oxygen treatment (COT). We compared the length of stay (LOS) in hospital and the rate of non-invasive positive pressure ventilation (NPPV) use according to baseline bicarbonate levels using the log-rank test or Cox proportional hazard model. Results: In the high bicarbonate subgroup (n = 165, bicarbonate 35.0[33.3–37.9] mmol/L, partial pressure of arterial carbon dioxide [PaCO₂] 56.8[52.0–62.8] mmHg), patients supported by HFNC had a remarkably prolonged LOS in hospital when compared to COT (HR 1.59[1.16–2.17], p = 0.004), whereas patients in the low bicarbonate subgroup (n = 165, bicarbonate 28.8[27.0–30.4] mmol/L, PaCO2 48.0[46.0–50.0] mmHg) had a comparable LOS in hospital regardless of respiratory support modalities. The rate of NPPV use in patients with high baseline bicarbonate level was significantly higher than that in patients with low baseline bicarbonate level (19.4 % vs. 3.0 %, p < 0.0001). Patients with high bicarbonate level in HFNC group had a lower rate of NPPV use compared to COT group (15.4 % vs. 23.0 %, p = 0.217). Conclusions: Among patients with non-acidotic hypercapnic AECOPD with high baseline bicarbonate level, HFNC is significantly associated with a prolonged LOS in hospital, which may be due to the reduced escalation of NPPV treatment. Trial registration: clinicaltrials.gov