Data collection
Patients entered into the study were identified by two
means. Paramedics annotated ambulance report forms
to indicate patients who were entered into the trial to
facilitate subsequent identification of these patients by
the research team. The emergency department at
Royal Hobart Hospital also supplied a list of all
patients transported by ambulance with a respiratory
diagnosis, which the research team cross checked
against ambulance records to compile a complete list
of patients included in the study. We retrospectively
defined a subgroup with chronic obstructive pulmonary disease as those patients with a definite diagnosis of
chronic obstructive pulmonary disease, as defined by
national guidelines.5 A respiratory physician blind to
treatment allocation reviewed lung function data and
smoking history, from private and public medical
records. Only lung function data recorded in the five
years before study entry were considered. Patients with
no lung function data or who did not fulfil spirometric
criteria for chronic obstructive pulmonary disease
were excluded from the subgroup analyses. Royal
Hobart Hospital provided data on arterial blood gas
results taken within 30 minutes of arrival at the emergency department, requirement for invasive (endotracheal intubation) or non-invasive ventilation, the
length of stay in hospital, and mortality. Length of
treatment in the ambulance and oxygen saturation during prehospital management came from the Tasmanian Ambulance Service’s records. Data were
missing from both the ambulance and hospital patient
records, so the denominators vary among analyses.