High-concentration oxygen caused hypoventilation in asthma exacerbation pts (RCT, Thorax) - PulmCCM
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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.

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