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Troubleshooting common capnography challenges: 3 tips for better results

Following these capnography hacks will help set your care apart

Sponsored by Medtronic

By Tim Nowak for EMS1 BrandFocus

Capnography has become a staple EMS assessment tool not just for providers who want to investigate what’s causing the patient’s symptoms, but also for those who want to resuscitate patients experiencing cardiac arrest. Simply relying – or depending – upon the end-tidal carbon dioxide (EtCO2) value, however, is not enough! Clinicians, we need to look at the whole picture, literally!

If you think that waveform doesn't look quite right or that the numbers don't quite add up, then you might need to take a step back and troubleshoot the capnograph. (image/Getty)
If you think that waveform doesn't look quite right or that the numbers don't quite add up, then you might need to take a step back and troubleshoot the capnograph. (image/Getty)

Acquiring a capnograph is an essential component of this equation. Just like you would obtain a 12-lead ECG for a patient experiencing chest pain, you should equally obtain a capnograph for your patient experiencing dyspnea. The reasoning behind this is the diagnostics — the waveform, the EtCO2 values, and the patient’s clinical presentation. Taking all of this into consideration will help to guide you down the best path.

During times where the waveforms don’t seem to cooperate, or the numbers don’t seem to add-up, you may need to take a step back to troubleshoot a little bit. Is it the device you are monitoring with or the patient presentation?

Here are some situations where troubleshooting can be helpful, especially when your clinical diagnostics may not seem to align with your patient’s presentation.

First, Two Starting Points

Establishing a baseline for capnograph findings – just as you would for initial vital signs – is an important start to every clinical situation. By all means, if the patient needs emergent treatment or therapy, then attending to it is a must. But, if you have the ability to take a step back to obtain a “clean” set of vitals, a capnograph tracing, and a 12-lead ECG, then this will help you establish a clinical baseline for your patient’s EtCO2 value, waveform shape and respiratory rate when you arrive on-scene, compared to their vitals when you arrive at the hospital.

During this timeframe, you will more clearly be able to monitor trends. How has the patient’s decreased respiratory rate – through coaching – been able to affect their EtCO2? Or, has their deteriorating blood pressure correlated to a deteriorating EtCO2 as well? What about your nebulizer therapy, has it improved their capnograph waveform? Or, is it time to switch to CPAP therapy? By asking these questions, you’re establishing a baseline and then monitoring trends will certainly help to keep your clinical decision making on track, as well as indicate when (or if) troubleshooting may be necessary.

Case Scenario 1 – Poor Sampling

You arrive on the scene to find your patient in cardiac arrest. High-quality chest compressions are continued, intravenous or intraosseous access is obtained, defibrillation is performed, and an advanced airway is inserted. So, how can we tell if the CO2 that we’re acquiring is an accurate value?

Starting with proper connections, it’s imperative to make sure that your sampling devices are compatible with your receiving monitor, as this is key to providing accuracy and reliability in your measurements.

While many connections may look the same, different manufacturers may have slight variances in their sampling line capabilities that can alter the accuracy of the waveforms and values that are produced. In such instances, using a supraglottic airway device, or providing passive oxygenation to your patient with an inappropriate sampling device in place may provide you with false readings that aren’t caused by the patient’s condition. These inaccuracies may result in an inappropriate clinical diagnosis and subsequent treatment.

Assuring that your capnography sampling line connection is secure at the monitor, confirming you are not getting an occlusion or blockage message on your monitor and you are attached to the patient are three key elements to consider. Let’s face it, not all of our patients within the prehospital environment are NPO (without having food in their system) for greater than 12 hours. As a result, secretions, emesis, or even blood due to airway trauma can all result in occlusions within our sampling lines note that even though there may be secretions in the line – unless the monitor states occlusion or blockage you do not need to change the capnography sampling line. Even tangled messes within your sampling line can produce this dilemma.

1) Verify the line is without kinks or visual obstructions

2) Disconnect, then re-connect your sampling line if you have an occlusion or blockage message on the monitor.

3) Replace the line altogether if occlusion message still appears.

4) Also, ensure that you are waiting for the Microstream capnography sample line to initialize and autozero before attaching to a closed circuit.

Case Scenario 2 – Artifact

You regularly receive widely-variable EtCO2 readings on your monitor and your waveform presentations never look consistent. Why is that?

When the numbers don’t seem to be accurate – or the patient’s clinical presentation doesn’t really seem to be reflected on the monitor – there’s a possibility that you’re dealing with a little bit of artifact. Talkative patients, loose connections, or poorly-positioned monitoring devices can all falsely impact your capnograph and EtCO2 readings. As a result, a little troubleshooting may be necessary to combat these inaccuracies.

For starters, coaching your patient’s breathing – and their need to converse with you – can all positively impact the accuracy of your capnograph findings. Correlating to this, the method by which CO2 samples are received can be impacted by how your patient is breathing. Are they a mouth breather, or a nose breather? Do they have a nasal-septal defect, or are other anatomical factors playing a role in their inhalation-exhalation process? Assuring that you have the proper sampling lines in use can make-or-break your rule-out of artifact versus legitimate clinical findings.

Beyond some of the “simple fixes” to your artifact and misrepresented findings, it’s imperative that each clinician be able to differentiate between when a finding is truly inaccurate, versus when it’s accurate ... but your patient has a legitimate medical issue they’re facing. Ventilation-perfusion mismatches, morphologies within their waveform, and deteriorating circulatory status can all impact the findings on your patient’s capnograph. As a result, each clinician needs to hold a strong understanding of what the full benefits of capnography use are in the prehospital environment.

Case Scenario 3 – Mis-diagnosis

When you hear wheezing, you would naturally expect to see “shark fin” waves, right? Well, what if you didn’t see this? Is there a problem with your sampling – with your machine – or, is your diagnosis incorrect?

Just like an ECG print-out will lead you toward the correct interpretation of the patient’s cardiac rhythm, your printed capnograph will lead you toward the correct interpretation of your patient’s ventilatory pattern (presuming you have the right knowledge in place to make this differential diagnosis).

The phrase “not all that wheezes is asthma” comes to mind with this situation. While your 54-year-old patient presents with bilateral wheezing, his capnograph shows a “normal,” “box-shaped” waveform. Or, it presents as almost a reversed “shark fin” with an initial upward spike, followed by a sloping downward wave. This is due to lower airway obstruction and not necessarily bronchospasm. Understanding the interpretative differences in your capnograph waveforms will help you to differentiate between asthmatic versus other obstructive respiratory diseases, and ultimately, whether or not a nebulizer with bronchodilator medications – or moving straight toward positive pressure via CPAP (continuous positive airway pressure) – is a better first-line treatment option.

Each of these situations, regardless of the cause or need for your troubleshooting actions, is hinged-upon your understanding of this invaluable piece of diagnostic technology.

Establishing a baseline will allow you to more accurately trend your patient’s condition. Looking for signs of poor sampling or artifact findings will help you to differentiate between what is real, versus what is inaccurate. And, having the education and understanding behind the use of capnography in the prehospital environment will help to direct your differential diagnosis and clinical decision-making pathway.

Given the proper equipment and set-up, your monitor will give you the answers that you need, as long as you know what to look for in the first place.

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