Hugh Greenbaum

In my book, I stated that ETCO₂ should not be considered as a "fifth vital sign" primarily due to the expense of the sensors.  While preparing an article for a jounal (more about that in a later entry), a reviewer asked if the monetary cost was really as exorbitant as I thought.  So I looked at the cost of the SpO₂ sensors that are commonly used in hospitals and some EMS agencies as a point of comparison.  To my surprise, these sensors are more expensive than the ETCO₂ sensors, yet nobody seems concerned that we use these on nearly every patient.  Which left me wondering:  If cost is not a barrier, should ETCO₂ be added to our list of vital signs?

What makes a sign "vital"?  It has to be non-invasive and provide a quick indication of the status of one or more "vital" functions of the body.  The patient's pulse gives us insight into the functioning of the patient's heart.  SpO₂ yields an indication of how well (or poorly) oxygen is being distributed to the body.  Blood pressure provides a measure for the "tone" of the vascular system, which impacts perfusion and the function of the heart itself.  And the respiratory rate tells us about the functioning of the respiratory system.  Measuring ETCO₂ is non-invasive and simple to perform, provides insights into the body's perfusion and metabolic  (both vital functions of the body), thus it fits the "pattern" of a "vital sign."  Maybe we should add ETCO₂ as our next vital sign.

Capnography is different from the current vital signs in that it requires a (currently) very expensive piece of equipment to sample the patient's exhaled gases, perform the analysis, and present the results to the provider.  SpO₂ was "adopted" as a vital sign only after measuring devices became (relatively) inexpensive.  On the other hand, the current generation of hospital and EMS patient monitors have capnography built-in or available as a plug-in module, making the tool ubiquitous (if still a tad expensive).  On the other hand, capnography enabled monitors are still too expensive for family practice providers.  So maybe ETCO₂ measurement is not yet ready for "prime time."

A bigger concern is that once a sign becomes a vital sign, we measure it reflexively even if there is no indication that the test is relevant to the patient's condition (i.e., is likely to change the course of treatment).  Do we really need an SpO₂ measurement (much less two) for an uncomplicated ankle injury?  What is the value in measuring the blood pressure when the patient's chief complaint is an uncomplicated dog bite to a hand?  We should be reserving tests, and let's face it that's what vital sign measurements are, for the patient's who need them.  Not every patient needs to have their ETCO₂ measured, much less monitored.  The counter to this argument is that the tests are non-invasive, iindividually inexpensive (i.e., we do not have to buy a new monitor for every patient), and lack side-effects, we should perform them every patient, every time, so we do not miss one or more on a patient who truly needs them.

On the other hand, emergency medical providers, regardless of the letters after your name, are supposed to think, not blindly follow protocols.  I do not like to do something "to" my patients just to check a box or because "It Is Written".  Once a measurement becomes a vital sign, we lose the ability to decide if it makes sense.  It is unsettling to explain to a patient that I'm putting this sensor on their nose because I have to, rather than it makes sense for their condition.  Of couse, I've never had a patient ask why I measured their blood pressure, pulse, etc..

The arguments for designating ETCO2 as a vital sign are sound.  The arguments against are not as strong.  As of today, I'm still undecided.  I will have to make-up my mind relatively soon, as I know I'll be asked about this eventually and I'll need a better answer than "I'm still thinking about it."  I will absolutely need an answer in time to create the second edition of Emergency Capnography!

Thank you dear reader for slogging your way through.  Please drop me a note and tell me what you think.  Stay safe out there!