I do not want to come off as anti-technology. In fact, quite the opposite, I
LOVE my technology. That is why my 2nd career is as a Respiratory Therapist. I have easily a million dollars worth of technology to use in the ICU and sometimes on just one patient. And, that is why I advise anyone to use caution when using technology. Technology can lead you down the wrong path if you are only looking at one number and "searching for a diagnosis from that number".
There are so many variables when using Pulse Ox and ETCO2 that can give you a false sense of security thus you may under treat. In the ICU we only take each number for worth if we can correlate it with other data along with the clinical status of the patient.
An SpO2 of 100% may look great but the patient may have a Hb of 8 g/dl or less which makes for poor O2 carrying capacity. (norm Hb 12 - 16 g/dl) And yes, this patient may complain of shortness of breath. Are you going to tell them "you can't be short of breath, your SpO2 is 100%"?
If a patient is septic, SaO2 and SpO2 are monitored but are not of as much value as the SvO2. Sepsis protocols run on SvO2 and MAP (Mean Art. Pressure). FiO2 and meds to increase the MAP will be utilized to maintain the SvO2.
TBI patients will also have their SvO2 monitored. That is how we discovered the days of hyperventilating to a PaCO2 in the 20s was not beneficial for the gray matter.
I mentioned in a earlier post about how pts will work hard to maintain homeostasis and survive...until they fail. That is why even ABGs are of little value in many pre-intubation cases.
When people think of COPD, they right away think of a CO2 retaining emphysema pt. Actually only 5% of all COPD patients are CO2 retainers. COPD is a very broad term.
Also even the emphysema pt can have restrictive components. Asthma; is it always obstructive or can it be restrictive? Obesity? Auto-immune lung diseases are yet another category which defy most ventilation principles. Lung cancer patients are also difficult to monitor and guess what their PaCO2 or PetCO2 will be.
How about the marathon runner that gets chest pain during a run? What do you think the normal PetCO2 would be on a pt that can have a large VO2 max.?
Yes, it may be possible to trust ETCO2 to correlate with the PaCO2 if the patient has no parenchymal lung disease and is just the average 30y/o non-smoking person. But then, would they need a paramedic with a PetCO2 monitor?
I usually play games with new physician interns. I have them bet on ABGs based on pt history. Sometimes I'll even let them look at CXRs. I don't let them look at other lab values though. They, too, will stereotype pts into what should be a typical ABG for a 100 pk/yr smoker. I may also throw in a pt with a non smoking hx but has Alpha 1 Antitrypsin Deficiency. We can also get into mixed diseases; Asbestosis/Emphysema, Sarcoidosis/Asthma etc. And then you have the various PNAs. Each one may behave differently. Necrotizing Staph PNA and PCP will give you two very different presentations and both will be a difficult ventilator management. The ETCO2 on each may be all over the map.
Now you put all this with clinical pictures that include hypovolemia, age, decreased cardiac output due to long term disease, vasopressors etc and your ETCO2 is anybodys guess.
Of course, you will get patients that truly display disease processes but have not been diagnosed.
Good waveforms may give you some indication of what you are dealing with but usually on a sidestream monitor there is artifact.
In most cases, if it is a long transport, all you can do is monitor a trend.
I can give you one mishap example where a well meaning CCT, but not well versed in ETCO2, thought the the patient was being over ventilated when they saw a low ETCO2. Thus, in transport they decreased the rate from 24 to 12 in attempt to get the ETCO2 to "normal". That pt did not arrive in good shape.
RRTs, RNs and MDs that work in hospitals are bombarded with sales pitches on drugs and technology almost every week. Plus, we go to conferences that have over 300 vendors. Everybody has a sales pitch. When someone thinks the BS factor is getting high, they'll ask, "where is the Cappuccino spout"? That usually lets the salesperson know he/she has a tough informed audience. Yes, even in the hospital we are sometimes suckered into buying junk either in function or use.
I've also seen some of the stuff that EMS has been sold through the years. How many different splints have been presented to the market throughout the years? And, what about all the CPAP devices that are on the market now? I recently got a Paramedic a little upset who had suggested the hospital buy the same little "mask/valve" device his agency was using. Give up RTs' devices that can cruise at 240 liters/minute? That's like comparing YUGO and Porsche.
One more good article with good reference studies sited:
http://www.aacn.org/pdfLibra.NSF/Files/Frakes/$file/Frakes.pages.pdf
