How to read waveform capnography
Other platforms explain it with text and video. In VMS you practice it on the patient.
Capnography shows every breath. It confirms an airway, measures ventilation and tells you how good your CPR is.
Step by step
Normal value
End-tidal CO2 is normally 35 to 45 mmHg with a square-shaped waveform for each breath. [1]
Confirm an airway
A steady waveform breath after breath confirms the tube or supraglottic airway is in the airway. No waveform means it may be in the esophagus. [1]
High numbers
Above 45 mmHg: the patient is not breathing enough (hypoventilation), for example after opioids or sedation. [1]
Low numbers
Below 35 mmHg: breathing too fast, or poor blood flow (shock, cardiac arrest). [1]
Shape
A sloped "shark fin" shape suggests narrowed airways (asthma, COPD). [1]
During CPR
Very low values suggest poor compressions. A sudden rise can be the first sign the heart has restarted. [2]
Sudden flat line
Check the patient, the airway and the tubing: disconnection, a dislodged tube or no breathing. [1]
Common errors
- Trusting chest rise alone to confirm a tube.
- Ignoring a slow rise in a sedated patient.
- Not checking the equipment when the line goes flat.
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
Facts and steps follow National EMS Education Standards (2021). VMS is not affiliated with these organizations. Updated: 2026-10-11.