Is hypercapnia associated with poor prognosis in chronic obstructive pulmonary disease? A long-term follow-up cohort study

• Published in: BMJ open Vol. 5; no. 12; p. e008909
• Main Authors: Yang, Hui, Xiang, Pingchao, Zhang, Erming, Guo, Weian, Shi, Yanwei, Zhang, Shuo, Tong, Zhaohui
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group LTD 15-12-2015; BMJ Publishing Group
• Subjects: Adult; Aged; Aged, 80 and over; Asthma; Body mass index; Chronic obstructive pulmonary disease; Cor pulmonale; Diabetes; Drug use; Female; Follow-Up Studies; Gases; Hospitals; Humans; Hypercapnia - diagnosis; Hypercapnia - etiology; Liver diseases; Male; Medical prognosis; Middle Aged; Patients; Prognosis; Proportional Hazards Models; Prospective Studies; Pulmonary arteries; Pulmonary Disease, Chronic Obstructive - complications; Pulmonary Disease, Chronic Obstructive - diagnosis; Pulmonary Disease, Chronic Obstructive - mortality; Qualitative Research; Recruitment; Risk Factors; Survival analysis; Survival Rate; United States > US; QUALITATIVE RESEARCH
• ISSN: 2044-6055; 2044-6055
• DOI: 10.1136/bmjopen-2015-008909

ObjectivesTo assess whether hypercapnia may predict the prognosis in chronic obstructive pulmonary disease (COPD).DesignProspective cohort study comparing the survival of patients with COPD and normocapnia to those with chronic hypercapnia.SettingPatients with consecutive COPD were enrolled between 1 May 1993 and 31 October 2006 at two medical centres. Follow-up was censored on 31 October 2011.ParticipantsA total of 275 patients with stable COPD and aged 40–85 years were enrolled. Diagnosis of hypercapnia was confirmed by blood gas analysis. Patients with near-terminal illness or comorbidities that affect PaCO2 (obstructive sleep apnoea, obesity-related hypoventilation, or neuromuscular disease) were excluded. The outcome of 98 patients with normocapnia and 177 with chronic hypercapnia was analysed.Outcome measuresOverall survival.ResultsMedian survival was longer in patients with normocapnia than in those with hypercapnia (6.5 vs 5.0 years, p=0.016). Multivariate COX regression analysis indicated that age (HR=1.043, 95% CI 1.012 to 1.076), Charlson Index, which is a measure of comorbidity (HR=1.172, 95% CI 1.067 to 1.288), use of medication (HR=0.565, 95% CI 0.379 to 0.842), body mass index (BMI) (HR=0.922, 95% CI 0.883 to 0.963), PaCO2 (HR=1.026, 95% CI 1.011 to 1.042), Cor pulmonale (HR=2.164, 95% CI 1.557 to 3.006), non-invasive positive-pressure ventilation (NPPV) (HR=0.615, 95% CI 0.429 to 0.881) and per cent of forced expiratory volume in 1 s (FEV1%) (HR=0.979, 95% CI 0.967 to 0.991), were independent risk factors for mortality.ConclusionsIncreased age, Charlson Index, chronic hypercapnia and Cor pulmonale, and decreased FEV1%, use of medication, BMI and NPPV, were associated with a poor prognosis in patients with COPD.