Wednesday, December 08, 2010

Emergency treatment of COPD: high flow oxygen and mortality

A recent BMJ paper reported:

Interventions High flow oxygen treatment compared with titrated oxygen treatment in the prehospital (ambulance/paramedic) setting...

Results In an intention to treat analysis, the risk of death was significantly lower in the titrated oxygen arm compared with the high flow oxygen arm for all patients (high flow oxygen n=226; titrated oxygen n=179) and for the subgroup of patients with confirmed chronic obstructive pulmonary disease (high flow n=117; titrated n=97). Overall mortality was 9% (21 deaths) in the high flow oxygen arm compared with 4% (7 deaths) in the titrated oxygen arm; mortality in the subgroup with confirmed chronic obstructive pulmonary disease was 9% (11 deaths) in the high flow arm compared with 2% (2 deaths) in the titrated oxygen arm. Titrated oxygen treatment reduced mortality compared with high flow oxygen by 58% for all patients (relative risk 0.42, 95% confidence interval 0.20 to 0.89; P=0.02) and by 78% for the patients with confirmed chronic obstructive pulmonary disease (0.22, 0.05 to 0.91; P=0.04). Patients with chronic obstructive pulmonary disease who received titrated oxygen according to the protocol were significantly less likely to have respiratory acidosis (mean difference in pH 0.12 (SE 0.05); P=0.01; n=28) or hypercapnia (mean difference in arterial carbon dioxide pressure −33.6 (16.3) mm Hg; P=0.02; n=29) than were patients who received high flow oxygen.

In their discussion section the authors concluded:

However, resources for an aggressive campaign of education will still be needed to change the “more is better” oxygen culture that may ignore the potential dangers of hyperoxia.

The more is better oxygen culture may be driven in part by overconfidence in pulse oximetry. COPD patients who are decompensated may have respiratory acidosis which shifts the oxy-hemoglobin dissociation curve to the right due to the Bohr effect. This causes hemoglobin to unload oxygen to tissues more readily, resulting in a lower saturation for a given PO2. Knee jerk reactions to such low saturations, however well intended, may have adverse consequences.


james gaulte said...

It was basic pulmonary disease 101 in the late 1960s ( t least that long ago) that you did not give high flow nasal 02 to a COPD patient who was having an exacerbation.We believed that would depress respiration and a high pco2 would go even higher.In training, more than once we saw patients who were conscious when the ambulance came but arrived in the ER in coma having being subjected to high flow o2 on route. Has the use of the pulse oximeter caused us to forget that lesson?

R. W. Donnell said...

Pulse oximetry---so easy to use, so misunderstood.