Normal end tidal co2 values

smartnurse1982 · Jun 22, 2008

have a quick question- The physician had requested an end tidal co2 on a trach and vent pediatric patient. to make a long story short, i called the doctor after it was done (it was 30) and told him it was low, the patient may have alkalosis (from what i remember 15 years ago normal values are 35-45) and he told me that was perfectly normal. have values been revised since i last came out of school?

oops-typo 5 years ago in lpn school we learned 35-45, not 15( i was only 11 then)

ukstudent · Jun 22, 2008

Yes and No. PaCO2 normal levels are 35-45. End tidals reflect the PaCO2 level but are not the same number. An ABG needed to be done to find out the CO2 gradient.

GilaRRT · Jun 22, 2008

Well, the EtCO2 value is simply a number. Yes, the generic "normal" is considered 35-45; however, any number of conditions can cause a change that may or may not be considered "normal" for any given patient.

For example, a patient in DKA may have a very low EtCO2. While this may not be considered "normal," it may be a "normal" physiological response to the metabolic acidosis seen in somebody with DKA.

As stated earlier, EtCO2 is a reflection of PCO2; however, you will need to know the EtCO2 to PCO2 gradient to make further sense of the relationship of these two numbers. In addition, anything that significantly alters hemodynamics can alter the EtCO2 to PCO2 gradient.

texas2007, BSN, RN · Jun 23, 2008

In Nicu, we did end tidal while drawing a cbg once just to see...I believe the end tidal was 20 points or so lower than the co2 on the cbg....60 vs. 40. The RT said that difference is normal.

-MNC_RN- · Jun 23, 2008

EtCO2 values are looked at in relation to PaCO2 values. Remember that all numbers in critical care must have a second number or observation to validate the first.

In the case of EtCO2, what matters is how it reflects the PaCO2. Take, for example, a patient with massive head injury. The neurosurgeon may want EtCO2 monitoring and want to keep the PaCO2 between 30 and 35. We would hook up the EtCO2 and record the number (I'll say 32) at the time the ABG is drawn. If the ABG comes back with a PaCO2 of 36, I now know that there is a difference of -4. In order to help me guide my vent, I now know that I want to make adjustments so that my EtCO2 reads between 26 and 31. This would be repeat correlated periodically per facility protocol to make sure that the relationship between the two still stands.

Being able to determine alkalosis from an EtCO2 would be very difficult, since you have no pH or base value with which to balance the acid in the equation. And, as explained, the EtCO2 may not reflect the exact PaCO2.

RegRT · Jul 12, 2008

have a quick question- The physician had requested an end tidal co2 on a trach and vent pediatric patient. to make a long story short, i called the doctor after it was done (it was 30) and told him it was low, the patient may have alkalosis (from what i remember 15 years ago normal values are 35-45) and he told me that was perfectly normal. have values been revised since i last came out of school?

End tidal Co2 ranges vary slightly from actual PaCo2 and can be affected by many factors depending on the condition of the patients lungs. For a person with "normal" lungs the difference between end tidal and Paco2 can vary between 5-8mmHg depending on the book your reading. So the short answer is you are right about the ranges 35-45 but that is for actual PaCo2 drawn from an ABG. As stated before end tidal is slightly different. It is best to get an ABG along side the end tidal to calculate the patients shunt. Once that has been done you can use an end tidal Co2 monitor as opposed to drawing multiple ABG's.