Compass is still being developed and is effectively in beta. Some content and features may be incomplete, change, or not work as expected.

Content is anchored to trusted sources where available, but Compass has not yet been clinically reviewed. It provides general information rather than medical advice.

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Tests and measurements

Capnography

Measuring carbon dioxide levels, through the skin or in breathed-out air, rather than only measuring oxygen.

What it means

Because carbon dioxide rises before oxygen falls when breathing muscles weaken, measuring it catches changes earlier. It can be recorded overnight through a small sensor on the skin, or sampled from the breath.

Why you might hear it

  • It may be added to an overnight study.
  • It is how a suspicion of carbon dioxide build-up is confirmed.

People who may help

Where Compass goes into this

About this explanation

These are plain explanations of words you may come across, not advice about your own situation. Where a word matters to a decision, the question pages go into it properly, and your own team is the place to take it.