The art of Capnography.

Dr. Jeffrey M. Goodloe delivered a very informative speech on the basic uses of capnography and made his case that it shouldn't be a purely paramedic skill set. The information was very concise and delivered a few distinct key points that I am going to try to convey to you all.

1. The ABC's of CO2 reading.

 

He used a very simple method of discerning what the different phases were, during phase one or the flat line before the first dramatic rise, we are at a near zero of CO2 due to the washing out by the oxygen being inspired. During phase two or the dramatic rise of CO2 we know that it is the exhalation that is giving us those numbers and it continues during the phase 3 for a very moderate increase up until the End Expiration number that we know as our CO2 reading. Beginning a very sharp drop for phase 4 is once again the washing out of CO2 from the monitor due to a huge increase of oxygen coming into the lungs. If phase two doesn't go sharply in an upstroke we can determine there may be some bronchospasm or occlusion that is not letting CO2 escape adequately. As this example points out.

If we don't see a rise at all or we see a gradual decrease in CO2 readings down to bellow normal in a few ventilations we can determine our intubation may not be in the proper place and in all likelihood we are in the esophagus.

Another way to look at it is:
AB is baseline, BC is the sharp upstroke that indicates the exhalation of the patient. CD is the plateau that ends with the highest CO2 reading available from the patient.
 
 

2. Normal ranges are PETCO2 of 35-45. An increase past 45 should prompt us to begin hyperventilating in an effort to get rid of more CO2 from our patients. A patient that is a COPD patient should be monitored closely because that patient's normal CO2 may be higher than average with some patients in exacerbation of COPD could show signs as high as 100 with a norm in the 50s usually.

3. He made a very strong case that EMT-Basics should be trained in the reading of CO2 so as to better assist with quickly determining if something has gone wrong with the ET tube or chest compressions in a cardiac arrest patient. The stress still seems to be in keeping SPO2 levels high, where CO2 readings especially for a conscious and breathing patient don't carry the same weight. We should be looking at inline ways to read both to get a better understanding of what is physiologically happening with our patients. If you look at the bottom graph a SPO2 reading will be picking up the reading at number 5. Pretty much only what oxygen levels are reaching the body tissue. With CO2 we will actually be getting the number happening post a complete loop in body and what is being brought out.

Together these numbers can greatly enhance our picture of the “whole” patient. Take for example a CHF and COPD patient with a CO2 of 50 an SPO2 of 88% and some gradually worsening respirations. The patient presents with lower extremity edema. We can with a quick view of a CO2 waveform determine if we are dealing with exacerbation of COPD or CHF and what our correct treatment should be.

If you notice in the first CO2 reading there is not a dramatic shift in the rise of CO2. After treatment you can see real time a gradual rise turn to a sharp rise as the COPD is alleviated at least to a degree with bronchodilation.

4. He finished his speech with talking about the 3 great sins of modern medicine as Ray Fowler has described.

  1. Unrecognized esophageal intubations
  2. Unsafe ambulance driving
  3. Paramedic-initiated no loads (pushed refusals)

Capnography has shown to decrease the incidence of unrecognized esophageal intubations dramatically. Some states including New York and South Carolina have now written in rules to mandate capnography for intubations and some locations have standing orders to place in-line CO2 detection within 60 seconds.

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