This was a nationwide prospective consecutive cohort study with longitudinal follow-up of patients starting long term oxygen therapy for COPD diagnosed by a physician and registered between 1 October 2005 and 30 June 2009 in the national Swedevox Register. The Swedevox Register covers about 85% of patients starting long term oxygen therapy for COPD in Sweden.16 (link) To increase the specificity of the diagnosis, we included only patients aged 45 or older. The exclusion criterion was a diagnosis of lung cancer at the start of oxygen therapy (baseline). A previous study that used this database and details of the study design have been published elsewhere.17 (link)
We obtained data on comorbidity and hospital admission for four years before baseline from the National Patient Register for inpatient and outpatient care, which covers more than 99% of all admissions in the study period and about 80% of all hospital based outpatient care since 2001 in Sweden.18 Definitions of the comorbid diagnoses have been published elsewhere.17 (link)
Data on all dispensed prescriptions during outpatient care after 1 July 2005 were obtained from the Swedish Prescribed Drug Register.19 (link) Drugs were categorised according to the Anatomical Therapeutic Chemical Classification System (ATC codes)20 as antidepressants (N06A), benzodiazepines (N05BA), weak opioids (N02AA59, N02AX02), strong opioids (N02A except weak), and sleeping pills (N05C), and as previously described.17 (link) Vital status was obtained from the Swedish Causes of Death Register.
We obtained data on comorbidity and hospital admission for four years before baseline from the National Patient Register for inpatient and outpatient care, which covers more than 99% of all admissions in the study period and about 80% of all hospital based outpatient care since 2001 in Sweden.18 Definitions of the comorbid diagnoses have been published elsewhere.17 (link)
Data on all dispensed prescriptions during outpatient care after 1 July 2005 were obtained from the Swedish Prescribed Drug Register.19 (link) Drugs were categorised according to the Anatomical Therapeutic Chemical Classification System (ATC codes)20 as antidepressants (N06A), benzodiazepines (N05BA), weak opioids (N02AA59, N02AX02), strong opioids (N02A except weak), and sleeping pills (N05C), and as previously described.17 (link) Vital status was obtained from the Swedish Causes of Death Register.
