Strengths and limitations of study
One limitation of our trial was the lower than expected
rate of adherence to study protocols, in both prehospital oxygen treatment and the measurement of arterial
blood gases on arrival at hospital, showing the difficulties associated with modifying practice. Of the 214
patients with confirmed chronic obstructive pulmonary disease, ambulance records showed that 37%
received treatment that did not comply with the study
protocol (56% in the titrated oxygen arm and 21% in
the high flow oxygen arm). In the titrated oxygen arm,
all protocol violations involved administration of high
flow oxygen at some point during prehospital treatment. We expect that this would have minimised any
treatment effect in the intention to treat analysis, but we
still found a significant reduction in mortality for
titrated oxygen treatment. The frequent lack of compliance in the titrated oxygen arm is probably a result
of the entrenched culture and training in emergency
medicine, which emphasises that high flow oxygen
will save lives in acute respiratory emergencies by preventing severe hypoxaemia. From reviews of charts
and interviews with paramedics, we found no evidence
that the breaches of protocol were a result of malfunction of monitoring of saturation (oximeter), patients
requesting more oxygen, or lack of understanding of
the protocol. However, feedback indicated that some
paramedics were concerned about insufficient delivery
of oxygen in distressed patients, which suggests that
they believed the entrenched cultural training that
“ more is better.” This culture, combined with the
absence of high quality evidence on the potential dangers of oxygen, may have been responsible for the
ongoing practice of routine delivery of high flow
oxygen.7 8 16 17 19-21 33-35
A second limitation of this study was the low rate of
arterial blood gas sampling for study patients.
Although we informed staff in the emergency department staff of the importance of arterial samples for this
trial, compliance was low and only 11% of arterial samples were drawn within 30 minutes of arrival. An audit
of oxygen treatment in the prehospital setting by Wijesinghe et al also found a low rate of arterial blood gas
sampling for patients with acute exacerbations of
chronic obstructive pulmonary disease.20 The authors
suggested several potential reasons for this, including
refusal by patients, reluctance of the doctor to do the
test, a perception by the doctor that the test is not indicated, or limited time and staff resources.20 In the emergency department at the time of the trial, the reasons
given mainly related to limitations in staff time and
resources but also to reluctance to do tests regarded
as not clinically indicated. This supports again the difficulty in “real world” clinical trials of getting clinicians