Hypo- and Hypercapnia and Mortality in Oxygen-Dependent COPD
Hypo- and Hypercapnia and Mortality in Oxygen-Dependent COPD
Background The prognostic role of the arterial blood gas tension of carbon dioxide (PaCO2) in severe Chronic Obstructive Pulmonary Disease (COPD) remains unknown. The aim of this study was to estimate the association between PaCO2 and mortality in oxygen-dependent COPD.
Methods National prospective study of patients starting long-term oxygen therapy (LTOT) for COPD in Sweden between October 1, 2005 and June 30, 2009, with all-cause mortality as endpoint. The association between PaCO2 while breathing air, PaCO2 (air), and mortality was estimated using Cox regression adjusted for age, sex, arterial blood gas tension of oxygen (PaO2), World Health Organization performance status, body mass index, comorbidity, and medications.
Results Of 2,249 patients included, 1,129 (50%) died during a median 1.1 years (IQR 0.6–2.0 years) of observation. No patient was lost to follow-up. PaCO2 (air) independently predicted adjusted mortality (p < 0.001). The association with mortality was U-shaped, with the lowest mortality at approximately PaCO2 (air) 6.5 kPa and increased mortality at PaCO2 (air) below 5.0 kPa and above 7.0 kPa.
Conclusion In oxygen-dependent COPD, PaCO2 (air) is an independent prognostic factor with a U-shaped association with mortality.
Advanced chronic obstructive pulmonary disease (COPD) is associated with high morbidity and mortality. Although long-term oxygen therapy (LTOT) decreases mortality in patients with advanced COPD and chronic hypoxemia, the prognosis is poor with a mortality rate of 51% at 2 years. Predictors of mortality in oxygen-dependent COPD include sex, age, body mass index (BMI), comorbidities, forced expiratory volume in one second (FEV1), and arterial blood gas tension of oxygen (PaO2).
The prognostic role of PaCO2 in oxygen-dependent COPD remains unknown. PaCO2 while breathing air, PaCO2 (air), has been associated with both increased mortality, decreased mortality, and no association with mortality.
Defining the predictive role of PaCO2 (air) on mortality is important for several reasons. Despite the data being inconsistent, clinicians often regard hypercapnia (PaCO2 > 6.5 kPa) as an indicator of more severe respiratory disease, worse prognosis, and higher risk of complications from oxygen therapy including respiratory depression. High-flow oxygen given pre-hospital to patients with likely COPD exacerbation was recently associated with increased risk of acute hypercapnia and mortality. Guidelines recommend titration of oxygen dose in hospital to avoid possible adverse effects when LTOT is initiated in a patient with hypercapnia. Hypercapnia might indicate the presence of a concurrent hypoventilation syndrome in COPD, which is associated with shorter survival. In addition, knowledge on predictors of mortality is needed as a prognostic model for patients with oxygen-dependent COPD is lacking.
The aim of this nationwide prospective study was therefore to estimate the association between PaCO2 (air) and mortality in oxygen-dependent COPD.
Abstract and Introduction
Abstract
Background The prognostic role of the arterial blood gas tension of carbon dioxide (PaCO2) in severe Chronic Obstructive Pulmonary Disease (COPD) remains unknown. The aim of this study was to estimate the association between PaCO2 and mortality in oxygen-dependent COPD.
Methods National prospective study of patients starting long-term oxygen therapy (LTOT) for COPD in Sweden between October 1, 2005 and June 30, 2009, with all-cause mortality as endpoint. The association between PaCO2 while breathing air, PaCO2 (air), and mortality was estimated using Cox regression adjusted for age, sex, arterial blood gas tension of oxygen (PaO2), World Health Organization performance status, body mass index, comorbidity, and medications.
Results Of 2,249 patients included, 1,129 (50%) died during a median 1.1 years (IQR 0.6–2.0 years) of observation. No patient was lost to follow-up. PaCO2 (air) independently predicted adjusted mortality (p < 0.001). The association with mortality was U-shaped, with the lowest mortality at approximately PaCO2 (air) 6.5 kPa and increased mortality at PaCO2 (air) below 5.0 kPa and above 7.0 kPa.
Conclusion In oxygen-dependent COPD, PaCO2 (air) is an independent prognostic factor with a U-shaped association with mortality.
Introduction
Advanced chronic obstructive pulmonary disease (COPD) is associated with high morbidity and mortality. Although long-term oxygen therapy (LTOT) decreases mortality in patients with advanced COPD and chronic hypoxemia, the prognosis is poor with a mortality rate of 51% at 2 years. Predictors of mortality in oxygen-dependent COPD include sex, age, body mass index (BMI), comorbidities, forced expiratory volume in one second (FEV1), and arterial blood gas tension of oxygen (PaO2).
The prognostic role of PaCO2 in oxygen-dependent COPD remains unknown. PaCO2 while breathing air, PaCO2 (air), has been associated with both increased mortality, decreased mortality, and no association with mortality.
Defining the predictive role of PaCO2 (air) on mortality is important for several reasons. Despite the data being inconsistent, clinicians often regard hypercapnia (PaCO2 > 6.5 kPa) as an indicator of more severe respiratory disease, worse prognosis, and higher risk of complications from oxygen therapy including respiratory depression. High-flow oxygen given pre-hospital to patients with likely COPD exacerbation was recently associated with increased risk of acute hypercapnia and mortality. Guidelines recommend titration of oxygen dose in hospital to avoid possible adverse effects when LTOT is initiated in a patient with hypercapnia. Hypercapnia might indicate the presence of a concurrent hypoventilation syndrome in COPD, which is associated with shorter survival. In addition, knowledge on predictors of mortality is needed as a prognostic model for patients with oxygen-dependent COPD is lacking.
The aim of this nationwide prospective study was therefore to estimate the association between PaCO2 (air) and mortality in oxygen-dependent COPD.