This prospective study of patients hospitalised with acute exacerbations of obstructive airway disease in five university hospitals in the Nordic countries has been described previously [8, 9].
The departments included were: The Department of Respiratory Medicine and Allergology, Akademiska sjukhuset, Uppsala, Sweden; The Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway; The Department of Respiratory Medicine, Tampere University Hospital, Tampere, Finland; The Department of Respiratory Medicine, Vifilstadir University Hospital, Gardabaer, Iceland; and The Department of Respiratory Medicine, Hvidovre Hospital, Copenhagen Denmark. An Internal Review Board in each centre or country approved the study.
Consecutive patients from each of the participating hospitals were included, provided that they had been admitted with acute exacerbations of COPD during 2000–2001. An acute exacerbation was defined as a change in condition in a COPD patient from baseline that was of such a magnitude that the patient needed an acute hospital admission. All patients fulfilled the criteria for COPD according to stage 1 or higher of the Global Initiative for Chronic Obstructive Pulmonary Disease . All records were reviewed by the investigators to confirm the diagnosis and GOLD criteria were used to diagnose COPD. Patients thought to have asthma were excluded. Only patients who were admitted for more than 24 hours were included. All patients signed an informed consent before entering the study.
The following data were collected at discharge from the respective pulmonary departments. Information was collected in a similar fashion on standardized data sheets in all the departments. All data were entered at one centre.
1. Questionnaire that included information on smoking history, type of living, and family situation (alone or with others).
2. Spirometry, body weight and height. Predicted values for forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were calculated based on the European Coal and Steel Union reference values . COPD severity was calculated according to the GOLD-criteria .
3. Health status (quality of life) was assessed using the disease-specific St George's Respiratory Questionnaire (SGRQ). It has three components: symptoms, activity and impact, in addition to total score . Higher scores indicate worse health status.
4. From the patients' records information was collected on treatment at discharge, including long-term oxygen therapy. The patients were categorized in four treatment categories based on the utilization of inhaled corticosteroids (ICS) and long-acting beta-2-agonists (LABA): none, only LABA, only ICS and both LABA and ICS . Assessment of co-morbidity was based on the diagnosis used by the treating physician. Diabetes mellitus was considered to be present if the patient was using medication for diabetes. Hypertension, ischemic heart disease or atrial fibrillation was considered to be present when diagnosed by attending physician.
5. Two years after discharge information regarding death and causes of death was obtained from the National Registries in each country. The primary (underlying) cause of death was divided into the following categories: Respiratory causes [acute COPD exacerbations (ICD 10 code J44.0 and J44.1), respiratory insufficiency (J96) and pneumonia (J12-J18)]; Cardio-vascular causes [myocardial infarction (I21), heart failure (I50), stroke (I61 and I63) and rupture of aortic aneurysms (I71)]; Malignancy [lung cancer (C34), leukaemia (C91), lymphoma (C85) and abdominal tumour (D37)] and Other [septic shock (R57), aspiration (J69) and ileus (K56)].