Study design

Weightings for individual CAT items were derived from qualitative analysis of focus group discussions with health professionals. One focus group was conducted with respiratory nurses and another with advanced respiratory trainees and respiratory physicians together. All participants provided signed informed consent prior to participating in a single focus group.

At the start of each focus group, the demographic and descriptive characteristics of participants and information regarding their current CAT usage were collected. Before and after the focus group discussion, all participants were asked to write down the three CAT items that they thought were most important and another three they considered least important in relation to respiratory-related hospitalizations.

During the focus group discussions, all CAT items were discussed and participants were asked if they thought the items were more important or less important in predicting the risk of respiratory-related hospitalizations and why. They were also asked to assign a weight difference between the most and least important items. Each focus group lasted approximately 1 hour. Investigator CAB was the moderator of the focus groups; investigators TWE and JMS were present to observe the discussion and to make notes. Each focus group discussion was audiotaped and later transcribed. After analysis, a summary of the focus group discussion and the adjusted item weightings were sent to the participants by e-mail.

Patient data were collected retrospectively by screening case notes and searching electronic patient databases between February and June 2014. Three hospital databases were screened for eligible patients: (a) patients in the Respiratory Integrated Care Service (RICS), a nurse practitioner led program directed towards intense case management of COPD patients with high rates of hospitalizations for COPD care; (b) patients receiving home oxygen therapy for their respiratory disease; and (c) patients visiting the outpatient clinic of a respiratory physician.

To be eligible for the current study, the patients had to meet the following criteria: (a) having a clinical diagnosis of COPD according to GOLD;⁵ (b) having completed the CAT at least 6 months ago while being in a stable phase of their COPD; (c) having no other serious lung diseases; and (d) having no terminal diseases (death likely within 12 months).

Approval for this study was given by the Southern Adelaide Clinical Human Research Ethics Committee (approval no. 553.13).

Based on expert opinion, we assumed that approximately 40% of the eligible patients (who had advanced disease) would be frequently hospitalized in the year after completing the CAT (defined as >1 hospitalization per year) because of respiratory problems. Assuming that a maximum of three characteristics would be included in the final multivariate model, a patient sample of approximately 80 was calculated to be sufficient to determine the multivariate model.

The primary outcome for the multivariate analyses was defined as the number of respiratory-related hospitalizations in 12 months after completion of the CAT.

Prior to the start of the study, literature was explored to define which patient variables needed to be considered for multivariate analyses because of their association with respiratory-related events (i.e. exacerbations, hospitalizations and/or death; Figure 1).

COPD patient characteristics associated with respiratory-related events (exacerbations/hospitalizations/death) and collected for all included patients. COPD: chronic obstructive pulmonary disease; FEV1: forced expiratory volume; mMRC: modified Medical Research Council dyspnoea scale; 6MWD: 6-minute walk distance. ^aThe window for valid lung function tests was defined as 6 months before and 6 months after completion of the CAT; if a lung function was not available in this window, it was defined as a missing. ^bNot tested in univariate analysis because of the high number of missing variables. ^cNot collected because in most medical records physical activity level was not clearly documented. ^dThe anticholinergic risk scale (ARS)¹⁸ estimates the risk of anticholinergic adverse effects of a drug (0: limited or no risk and 3: very strong risk). The ARS of the individual prescribed drugs were added up to provide the ARS score. The ARS score¹⁹ was adjusted according to Rudolph et al.¹⁸ by adding the inhaled agents tiotropium and ipratropium to the original ARS score. ^eThe medical history of each patient was reviewed to determine their co-morbidities.