More information is almost always better – especially when you’re walking into a scene with a patient you’ve never met. It’s rare that you start with a neatly packaged diagnosis. You usually get a vague complaint, a few scattered clues and a patient who may or may not be able to explain what’s going on. From that, you must put together a picture of what’s happening.
Beyond the 911 call, and maybe a quick history from the patient or bystanders, assessment starts with the first wave of vital signs – usually heart rate, respiratory rate, blood pressure, SpO₂ and temperature. The most important, though, is often capnography. End-tidal CO₂ (EtCO₂) gives you a real-time read on ventilation, metabolism and perfusion, all in one number and waveform. No other single vital sign or waveform does that. It’s why so many experts call capnography “the most important vital sign.”
A recent EMS1 webinar, “With or without capnography? How your assessment tools could change everything,” walked through several cases where EtCO₂, alongside other vitals and findings, helped crack the diagnosis.
A single vital sign can guide big decisions
The webinar, sponsored by Medtronic and Stryker, featured longtime paramedic/educator Chris Kroboth, MS, FP-C, owner and CEO of LifeLine EMS Training in Virginia, and emergency physician Jeff Goodloe, M.D., FACEP, CMO for the EMS system serving Oklahoma City and Tulsa, Oklahoma.
They kicked things off with a quick refresher on how the body produces CO₂, why certain devices give better readings and how newer sidestream capnography paired with bilateral nare sampling circuits offers cleaner, more reliable waveforms and values. Not all sampling sets are created equal – and when you’re making big treatment calls off their readings, quality matters.
“We’re going to make some pretty big decisions,” Goodloe said. “We’re going to make decisions about treatment plans, we’re going to make decisions about destinations, we’re going to make decisions about whether we would allow a patient-informed refusal or not. A lot of these things can hinge on even a single vital sign. And so having a truly accurate end-tidal CO₂ … can truly make a big difference in the optimal care planning and care delivery for these patients.”
Case #1: A minor crash that wasn’t
Police asked EMS to check out an elderly woman after a rear-end MVC. Both cars looked drivable, and she insisted she was fine. Her vitals looked OK: heart rate 74, blood pressure 124/80, SpO₂ 99%. She was dismissive and focused on getting to her friend’s house, with a noticeably anxious, dyspneic tone.
It’s important to approach all scenes with an open mind, Goodloe noted – avoid tunnel vision and assess fully and carefully. These scenes can have visual distractions and high emotions that complicate care.
“Even when things don’t necessarily look so bad, we still have to keep our assessment radar in full focus,” Goodloe said. “We basically have to make sure folks can truly prove they’re OK, not the other way around.”
Given the subject’s age, Goodloe said, it’s an occasion to be highly suspicious. Seniors, for instance, often have a history of high blood pressure and take medication for it – is this patient’s “normal range” BP normal for her? If her baseline is higher, the normal BP may be significant, and the same for the heart rate. “This set of vital signs,” Goodloe said, “should actually cause us reason to pause and really try to dig a little bit deeper.”
They revealed her EtCO₂ was 32 with a normal waveform – a little low – but her respiratory rate was 22. That’s not normal for an older adult sitting still.
“If you were to sit here for the remainder of this presentation and breathe 22 times a minute, almost all of you would start experiencing some paresthesias,” Goodloe said. He noted older adults often underreport pain and may be on medications that mask it. A low EtCO₂ paired with a high respiratory rate should ring alarm bells for hidden trauma, pulmonary contusion or maybe a small pneumothorax the patient doesn’t feel yet.
At the least this finding calls for further assessment, and it wouldn’t be inappropriate to take this patient to a higher-level trauma center with experience in geriatric trauma.
Case #2: Generalized weakness
Next up was a 78-year-old woman with generalized weakness and altered mental status. She was cool to the touch (unusual in the typically warm home of a senior), slouched in a chair, staring into space. Basic vitals: HR 85, BP 120/70 (MAP 86), SpO₂ 97%. Her EtCO₂ was 31, and her respiratory rate was 24.
For a senior who’s feeling weak and not active, the interesting finding here was the heart rate. Many older adults run lower resting heart rates, especially those on rate-controlling meds, so 85 can be relatively high in this context.
“That should be a concern,” said Kroboth. “Tachypnea in my brain goes to low perfusion problems – I think obstructive respiratory issues, asthma, COPD, or they have fluid in their lungs … That could create tachypnea. The other thing is a perfusion issue. Those are the two overall differential sets that jump to my head quickly, especially with an end-tidal of 31.”
The next areas to investigate in this situation would include temperature, time of onset and events leading up to the patient’s current state. Consider recent medication changes and compliance as well.
This patient turned out to be in early sepsis. Her heart rate was elevated (yes, 85 is elevated in a patient on a beta blocker), and the respiratory rate was an early sign of compensation. EtCO₂ was falling with her lowering perfusion – while her SpO₂ was still good, her pleth wasn’t. Her BP and MAP were fine, but after arriving the crew sat her up and assessed her, and those began falling too.
This case illustrated one of capnography’s biggest advantages: It’s continuous, instant and not affected by many medications. “That’s the beauty of the orange line,” Kroboth added.
Case #3: Pregnant and weak
The third case presented a female, 32, weak and nauseated. This patient’s age, Goodloe began, should prompt thought about comorbidities, potential toxidromes and recent trauma. It’s also childbearing age, and sure enough, this patient turned out to be visibly pregnant.
“Now we have two patients we’re taking care of,” said Goodloe. “Keeping the attention on mom [is] going to be the best care for fetus or fetuses.”
History, from the patient and/or family and friends, may help illuminate what’s happening. How late in the pregnancy is this woman, and what complications or comorbidities may be occurring at this stage? Has she had prenatal care? There could be cardiovascular, metabolic or endocrine-related problems occurring. Gestational diabetes is a possibility.
This scene doesn’t appear complicated, but again, Goodloe emphasized, make sure you’re not missing something small that can lead you to something big.
Initial vitals for this woman were heart rate 96, SpO₂ 97% and BP 108/70 (MAP 82) – nothing too alarming. Her EtCO₂ was revealed to be 30, with a respiratory rate of 24 and normal waveform.
That mismatch – fast breathing but low EtCO₂ – points toward dehydration or a metabolic problem. And one of the primary drivers of dehydration in third-trimester pregnancy is diabetes.
“I would be really interested in what a random fingerstick blood glucose is in this patient,” said Goodloe. “Her issue could start with D and transition through K and end in A [i.e., diabetic ketoacidosis].”
Sure enough, her glucose was 388 mg/dL. The best course for this patient is to start fluids and transport to a facility that has resources for labor and delivery.
“There’s a lot to be managed here, and look at what that one additional channel did,” said Goodloe. “It didn’t just trigger us into saying, ‘Uh-huh, we have some suspicions,’ but really … that led to that blood glucose as well.”
Case #4: Fall and breathlessness
A man in his 20s fell on some steps and complained of clavicle pain, speaking in short, terse sentences. His heart rate was 109, SpO₂ 98% and blood pressure 132/83 (MAP 99). He was pale and cool but not overtly unstable.
His end-tidal CO₂ was 46 mmHg, and his respiratory rate was 22. While he was breathing fast, he wasn’t ventilating well. This could be drugs, Kroboth noted, or some kind of lung issue like a pneumothorax, but either way signifies a problem.
The patient then became even more short of breath and changed to one-word sentences, and his end-tidal started to fall. In this case, rising pressure in his pleural cavity was starting to compress the vena cava – a simple pneumothorax progressing toward a life-threatening tension pneumothorax. That happens over time, not instantly, Kroboth emphasized, so be attuned during transport. Capnography shows the trend before the patient crashes.
Shape the right course of care
Across all four cases, capnography offered something no other vital sign did: continuous, real-time feedback on three major systems – respiratory, metabolic and circulatory. It filled in the blanks when traditional vitals looked fine and pushed clinicians to dig deeper.
End-tidal CO₂ has become even more valuable, reliable and easy to use. Incorporating capnography into every assessment isn’t just a “nice to have” – it’s a fast track to more accurate differentials and better patient outcomes.
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For more information, visit Medtronic.
