Acute Crit Care.  2019 Aug;34(3):202-211. 10.4266/acc.2019.00563.

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

  • 1Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.


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 (O2) therapy.
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.
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 (R2=0.378, P=0.010). The fraction of inspired O2 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 O2 improved over time in both groups.
Physiological parameters can improve after the use of an HFNC in patients with acute hypercapnic respiratory failure given low-flow O2 therapy via a facial mask. Further studies are needed to identify which hypercapnic patients might benefit from an HFNC.


hypercapnia; oxygen inhalation therapy; respiratory insufficiency

MeSH Terms

Carbon Dioxide
Hydrogen-Ion Concentration
Intensive Care Units
Observational Study
Oxygen Inhalation Therapy
Partial Pressure
Propensity Score
Respiratory Insufficiency*
Respiratory Rate
Carbon Dioxide


  • Figure 1. Flowchart showing the classification and propensity score matching of acute respiratory failure patients. HFNC: high-flow nasal cannula.

  • Figure 2. Sequential measurements of arterial partial pressure of carbon dioxide (PaCO2, A), pH (B), and arterial partial pressure of oxygen (PaO2, C) during the use of a high-flow nasal cannula.

  • Figure 3. Association between carbon dioxide (CO2) washout during the first 12 hours and initial arterial partial pressure of carbon dioxide (PaCO2) level.

  • Figure 4. Sequential measurements of respiratory rate (A) and heart rate (B) during the use of a high-flow nasal cannula.

  • Figure 5. Sequential measurements of fraction of inspired oxygen (FiO2, A) and oxygen (O2) flow rate (B) during the use of a high-flow nasal cannula.

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Acute Crit Care. 2022;37(1):120-123.    doi: 10.4266/acc.2020.00983.


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