Robert Murray Jr, NRP, MS, shares the components of a waveform and common capnography pitfalls
Robert Murray Jr., NRP, MS, deputy director of operations for Sussex County EMS in Delaware, and Medtronic consultant, presented a webinar titled “Capnography in EMS: Tube verification is only the beginning” as part of the PACE Medtronic Webinar Wednesdays series.
Murray discussed the main uses for capnography in the field and common capnography mistakes, and provided case examples his EMS group has experienced in the field.
Top quotes on prehospital capnography
Here are a few quotes from Robert Murray on using capnography in EMS:
“Regardless of how much technology we put in front of you, we can’t forget about the patient and actually taking a look at them.”
“It’s imperative that when we are monitoring CO2, we must have the waveform in our face. The number can give us a false sense of security.”
“Capnography allows us to be proactive and get ahead of the proverbial eight ball.”
Top takeaways on capnography use in EMS
Here are 4 takeaways from Murray’s presentation on capnography.
1. Components of a CO2 waveform
Three things are needed to have a capnography waveform:
- Perfusion. Heart needs to be circulating blood
- Ventilation. Air needs to be moving in and out
- Metabolism. Cells need to performing aerobic respiration
If you aren’t seeing a CO2 waveform, check ventilation and perfusion first, then start thinking about metabolism (sugars, bicarb, etc.). EtCO2 measures the amount of CO2 leaving the body. If blood isn’t circulating or air isn’t moving, then cells can’t get rid of CO2. If proper perfusion and ventilation is present, and EtCO2 is still low, aerobic respiration (metabolism) isn’t occurring.
2. Know your waveform
Murray described the components of a capnography waveform.
- Phase 1. Dead space ventilation (yellow) – patient isn’t exhaling or inhaling therefore air isn’t moving
- Phase 2. Beginning of exhalation (pink) – patient is exhaling alveolar CO2 rich air, the line should be almost vertical because CO2 is rapidly exiting the lungs
- Phase 3. Alveolar Plateau (red) – patient is continuing to exhale, an even flat line means that the alveoli are being evenly emptied
- Red Arrow. EtCO2, the maximum amount of CO2 that is exhaled
- Phase 4. Inhalation (green) – CO2 decreases as the patient inhales oxygen
3. Look at your waveform, not just your numbers
If you’re only watching your CO2 number, you may miss something. For example, a COPD patient may have an adequate EtCO2, but their waveform may display a “sharkfin” pattern. This pattern shows a flatter phase 2 and uneven phase 3 indicating that CO2 is taking longer to escape and that the alveoli aren’t emptying equally.
4. Moving in and out of a vehicle is risky for the ET tube
The most common time for an ET tube to become displaced is when you’re moving a patient into or out of your vehicle. Make sure that you keep an eye on your capnography before and after you make the move to ensure that your airway is still intact.
Additional capnography resources
For more information on EMS use of capnography with these resources: