RESULTS
We received consent to participate from 62 (98%) of
the 63 full time paramedic staff, who had a one
month familiarisation and training period before data
collection started. Paramedics were equally distributed
between the two treatment arms with regard to rurality,
training, and experience (table 1). The paramedics
transported 405 eligible patients to the Royal Hobart
Hospital during the 13 month study period: 226 were
treated by paramedics assigned to the high flow oxygen arm and 179 by those in the titrated oxygen arm.
The subgroup of patients with chronic obstructive pulmonary disease confirmed by lung function tests contained 214 of the study patients: 117 were treated by
paramedics assigned to the high flow oxygen arm and
97 by those in the titrated oxygen arm (figure).
Seventy-nine (37%) randomised patients, 25 in the
high flow arm and 54 in the titrated arm, did not
receive treatment according to protocol, leaving 43
patients in the titrated oxygen arm and 92 patients in
the high flow oxygen arm for the per protocol analyses.
Baseline characteristics for all patients and for the
subgroup of patients with confirmed chronic obstructive pulmonary disease did not differ significantly
between the treatment arms in terms of age, sex, initial
oxygen saturation, or prehospital treatment time
(table 2). Patients in the chronic obstructive pulmonary
disease subgroup did not differ significantly between
groups in per cent predicted forced expiratory volume
in one second or smoking history (table 2). Blood gas
samples were taken after arrival at hospital in only 122
(57%) patients, and of these only 23 (19%) were arterial
samples drawn within 30 minutes of arrival.
In the intention to treat analysis for all patients, we
found a significant difference between the two treatment arms for mortality (relative risk 0.42, 95% confidence interval 0.20 to 0.89; P=0.02) (table 3). Mortality
was 9% (21 deaths) in the high flow oxygen arm compared with 4% (seven deaths) in the titrated oxygen
arm. In the intention to treat analysis for the subgroup
with confirmed chronic obstructive pulmonary disease, we also found a significant difference in mortality:
9% (11 deaths) in the high flow arm compared with 2%
(two deaths) in the titrated oxygen arm (relative risk
0.22, 0.05 to 0.91; P=0.04) (table 3). All deaths
occurred after arrival at hospital, including two in the
emergency department and two in the intensive care
unit. Respiratory failure was the primary cause of death
in all cases, and approximately 70% of deaths occurred
within the first five days of admission for both treatment arms.
In the intention to treat analysis for secondary outcomes, we found no significant differences between
treatment arms for length of hospital stay or requirement for ventilation for all patients or the subgroup
with confirmed chronic obstructive pulmonary disease
(table 3). Arterial blood gas measurements did not differ significantly between groups, although only about
11% of patients had these done within 30 minutes of
arrival at hospital. The mean time to blood gas analysis
for all samples (venous and arterial) was 1 hour
41 minutes after arrival at hospital for the high flow
oxygen group and 1 hour 46 minutes for the titrated
group. Blood samples for gas analysis were drawn
from 59/97 (61%) patients in the titrated oxygen arm
and 63/117 (54%) in the high flow arm.