Capnography provides an immediate picture of a patient’s ventilatory status. The capnography waveform, or capnogram, reflects exhaled carbon dioxide (CO₂) levels and can indicate normal ventilation or specific clinical conditions. Each shape or variation in the waveform can signal a change in airway or breathing status.
Understanding normal and abnormal capnography waveforms in EMS
Capnography is one of the most powerful tools in the EMS toolbox. It tells us what’s happening with a patient’s ventilation, perfusion and metabolism — instantly and continuously. But to use it effectively, you have to understand what the waveforms are telling you.
Each waveform gives real-time feedback on how well your patient is breathing, how well they’re perfusing and whether your treatment is working. Here’s what to look for:
Normal and abnormal etCO2 capnography waveforms
Normal waveform
- A normal capnography waveform has a square shape: sharp upstroke, flat alveolar plateau and a quick return to baseline.
- This shows that exhaled CO2 is moving out efficiently. It’s what you expect to see in a well-ventilated patient with good perfusion.
Bronchospasm (“shark fin”)
- “Shark fin” — A sloped or prolonged Phase II upstroke with no clear plateau.
- Classic for asthma or COPD exacerbation.
- If you see this, think airflow obstruction. Treat with bronchodilators and monitor for improvement.
Increasing etCo2 (Hypoventilation)
- As respiratory rate or tidal volume drops, ETCO2 rises.
- Decrease in tidal volume, gradual increase in waveform height.
- Think: narcotic overdose, fatigue or head injury. Support ventilation early.
Decreasing etCO2 (Hyperventilation)
- When patients breathe too fast or too deeply, they blow off CO2.
- ETCO2 trends down, waveforms get shorter.
- Often a sign of anxiety, pain, acidosis or head trauma. Correct the underlying cause.
Rebreathing CO2
- When the baseline doesn’t return to zero, suspect CO2 retention.
- Common causes: faulty expiratory valve, or inadequate exhalation.
- Fix your equipment or adjust your technique.
Curare cleft
- A dip in the plateau that appears when a patient begins to breathe over the ventilator.
- Tells you the paralytic is wearing off — time to re-dose or adjust sedation.
Cardiac arrest
- Decreased or absent cardiac output
- Decreased or absent pulmonary blood flow
- Sudden decrease in CO2 values
ROSC
- Increased cardiac output
- Increased pulmonary blood flow
- Gradual increase in CO2 production
- Reassess pulses and rhythm
Bottom line: Capnography is more than a number — it’s a waveform, and every waveform tells a story. Know what normal looks like. Learn what abnormal means. And use that information to guide your patient care in real time.
EMS1 is using generative AI to create some content that is edited and fact-checked by our editors.
