Nov 242011

Even my neighbor's cat knows that giving high-concentration oxygen to people with COPD and acute hypercapneic respiratory failure can cause them to hypoventilate further, causing life-threatening respiratory failure. (And he's not even a very smart cat.)

Perrin, Beasley et al asked, does a similar mechanism operate in severe asthma exacerbations?

They randomized 106 patients presenting with severe asthma exacerbations at 3 urban emergency departments in New Zealand to receive either high concentration of oxygen (8 liters/min through a mask) or titrated oxygen to reach an arterial saturation of 93-95%.

They measured the transcutaneous partial pressure of carbon dioxide at baseline, 20, 40, and 60 minutes. (This method is far from 100% accurate, but it's been reported as being more consistently accurate than end-tidal CO2 monitoring, for example.)

At 60 minutes, those breathing high-concentration oxygen tended to have greater increases in their transcutaneous pCO2:

  • 22 of 50 (44%) in the high-oxygen group had increases in transcutaneous pCO2 of >= 4 mm, while only 10 of 53 (19%) in the titrated oxygen group did.
  • 22% (11 of 50) of the high-O2 group had an increase of 8 mm or more; only 6% (3 of 53) in the titrated O2 group did.
  • All the patients (10) who ended with a transcutaneous pCO2 of >= 45 mm were in the high-oxygen group. Five of them (10% of the high-oxygen group) had an increase of >= 10 mm.

There were no differences in outcomes reported.

This adds to another similar recent study we reported, in which people with obesity hypoventilation syndrome (in a stable state, not in exacerbations) were given 100% oxygen to breathe for several minutes, and crossed-over to act as their own controls on another day. They, too, had increases in their partial pressures of carbon dioxide, some quite significant.

Perrin K et al. Randomised controlled trial of high concentration versus titrated oxygen therapy in severe exacerbations of asthma. Thorax 2011;66:937-941.

Get our weekly email update, and explore our library of practice updates and review articles.

PulmCCM is an independent publication not affiliated with or endorsed by any organization, society or journal referenced on the website. (Terms of Use | Privacy Policy)


High-concentration oxygen caused hypoventilation in asthma exacerbation pts (RCT)