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This vital sign is still underutilized, but that’s going to change soon

Use of capnography is charging ahead for more accurate prehospital diagnoses and care


Sponsored by Medtronic

By Tim Nowak for EMS1 BrandFocus

One thing you can count on not hearing from a patient is a description of their acute asthma exacerbation, along with their guess on what their capnograph waveform is displaying.

Using capnography helps to put value into your patient’s clinical context.
Using capnography helps to put value into your patient’s clinical context. (image/Medtronic)

Capnography technology is a valuable yet underutilized vital sign in acute and critical care. That doesn’t mean it’s underappreciated, however, especially in EMS.

By all means, we’ve come a long way over the past decade since its introduction (I’m not talking about colormetric capnometry). There are certainly many EMS agencies out there leading the pack when it comes to capitalizing on the full assessment potential of this technological advancement, and kudos to them!

But there are still a handful of agencies (and even hospitals) that aren’t incorporating this tool into their regular patient assessments. To many clinicians in the prehospital and ED environments, capnography is only used to verify tube placement and not to its fullest extent as our true fifth vital sign.

Taking a systematic approach to tube checks

In EMS, we often associate capnography with advanced airway management. While this has become our gold standard in the prehospital environment, there’s certainly more to it than just tube confirmation.

Capnography incorporates ventilation and perfusion into a waveform, and then provides a numeric value, not the other way around. Having both the number and the waveform together is the key, because relying only on the number isn’t enough – especially with your patients that are alive with a pulse and a problem.

What happens when your capnograph waveform doesn’t show a shark fin?

Bilateral expiratory wheezing, accessory muscle use, audible dyspnea, pursed lips, tripod positioning – these all sound like signs that could lead your differential diagnosis and treatment down a number of noninvasive paths. So, which do you choose?

When you think about asthma, you anticipate seeing “shark fin” waveforms on your capnograph readout, but what if you don’t see them? What if your patient still presents with the same clinical symptoms? Remember, not all that wheezes is asthma, and not all that wheezes has a shark fin waveform. Non-shark fin waveforms could indicate other obstructive problems like COPD or pulmonary edema (even in the presence of wheezing).

Incorporating capnography interpretation into dyspnea patient assessment should be your ALS agency’s standard practice by now, and it’s becoming a standard practice for many BLS agencies, too. What’s often overlooked, though, is when your capnograph waveform doesn’t present with a shark fin – what should you do?

It’s time to look past solely relying on this symbol as an indicator for treatment. If you don’t know what to look for beyond shark fins (which really represent incomplete alveolar emptying) it’s time to get a little capnography continuing education under your belt!

Hypocapnea, but with normal breathing?

Wait, what? A patient presents with normal breathing, but with a low end-tidal carbon dioxide (EtCO2) level ... how is that?

Remember, capnography encompasses more than just ventilations – it also includes perfusion. In instances where you’ve got a ventilation/perfusion (V/Q) mismatch, there can certainly be more to the story than what hyper- and hypoventilations can lead you to. In fact, think about your post-resuscitation patient for a moment: If they’re still not breathing, then how in the world could they have a low EtCO2 value? Zero respirations should equate to high CO2 retention, right?

Capnography encompasses more than just ventilations – it also includes perfusion. (image/Medtronic)
Capnography encompasses more than just ventilations – it also includes perfusion. (image/Medtronic)

While this is correct, it’s only correct in the right context (of measuring ventilatory function). In the instance of post-resuscitation, or even in patients that are alert and alive – and without grossly abnormal respiratory rates – we’re measuring CO2 gas exchange as a perfusion or metabolic mechanism. That’s how we’re able to associate low EtCO2 values with elevated lactate values for sepsis patients, correlate V/Q mismatches to pulmonary embolism patients or even correlate grossly low EtCO2 values with biological death.

Simply saying that the patient’s EtCO2 value is “29” or “52” doesn’t really tell us anything – not without context, at least.

Putting this all into context 

Neck pain alone doesn’t automatically mean that your patient needs to be secured to a long spine board. Nor does a “normal” appearing capnograph waveform necessarily equate to no problems with a patient’s respiratory status. It’s all in the context, and context can only be applied if you understand how to use the technology, tool or information you have at hand.

Blood pressure, pulse rate, respiratory rate, pulse oximetry level and a capnograph waveform – these five vital signs can help to navigate your patient care down a number of differential diagnosis pathways. The key, however, is in understanding how and when to incorporate these underutilized (but not underappreciated) technologies into your patient assessment and care repertoire.

Simply saying that the patient’s EtCO2 value is “29” or “52” doesn’t really tell us anything. Using capnography helps to put value into your patient’s clinical context.
Simply saying that the patient’s EtCO2 value is “29” or “52” doesn’t really tell us anything. Using capnography helps to put value into your patient’s clinical context. (image/Medtronic)

After all, not every patient that we encounter has an expected underlying condition or identifiable problem. Sometimes we need to be prepared to identify and care for the unexpected, and capnography is opening the doors of possibility to do so.

Our patients’ most concerning problems often revolve around one of three physiologic components: perfusion, ventilation and metabolism. Using capnography helps to put value into your patient’s clinical context.

Visit CapnoAcademy for free educational videos and troubleshooting resources.

Read Next: Troubleshooting common capnography challenges: 3 tips for better results

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