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A Quick Guide for Student + Registered Veterinary Nurses ✨
Capnography is one of the most useful monitoring tools we have in practice - especially during anaesthesia! It gives us real-time information about how well our patient is breathing + circulating.
✨ What is capnography?
Capnography is a non-invasive way of measuring carbon dioxide (CO2) in the air a patient breathes in and out.
It shows us this information as a waveform (capnogram) over time.
✨ What does a normal capnogram look like?
A normal capnogram follows a simple pattern:
- CO2 starts at zero (which is the baseline)
- it rises during expiration
- reaches a plateau (alveolar plateau)
- then drops back to zero on inspiration
Think - up on breathing out, down on breathing in
✨ Common capnography patterns
Airway obstruction ("shark-fin")
- waveform looks slanted instead of square
- possible causes: mucous in ET tube, bronchospasm
Cardiogenic oscillations
- small wavy ripples on the plateau
- seen in - brachycephalic patients, barrel-chested patients, low respiratory rates
Hypercapnia (high CO2)
- increased ETCO2 values
- possible causes: hypoventilation, increased CO2 production, increased cardiac output
Decreasing ETCO2
- can be: gradual (leaks, hyperventilation) or sudden (disconnection, early signs of arrest)
Rebreathing
- waveform doesn't return to baseline
- possible causes: low fresh gas flow rate, exhausted soda lime, excessive dead space
✨ Why capnography matters
Capnography helps you quickly assess:
- ventilation
- airway patency
- equipment issues
- early signs of patient deterioration
✨ Quick takeaway
Normal = square wave, returns to zero
"Shark-fin" = obstruction
High CO2 = hypoventilation
Low CO2 = check patient/equipment
No baseline = rebreathing
I really hope this helps! For a quick-reference version, you can purchase my 'capnography' poster here:
Thank you so much for reading, Jade x