Question about CO2 Values

[daphneybly]

I'm working on my care plan and the normal CO2 values for our facility are 21-32 and my patient had two findings. The first finding is 14. Decreased CO2 can be caused by chronic diarrhea, which pt. has. (Pt has metastatic colon cancer) However, if I understand correctly, those levels are low based on having a history of the diarrhea, it is not something that is changed overnight. The finding 5 days later was 20, so that is 6 points higher but still low. I realize that the values can vary a little bit based on the draw, but that seems like a large variation. Is it? Can it still be the same reason for both (the chronic diarrhea) or should I try to look further into it? None of the other reasons for a decreased level fit my pt (loop diuretics, renal failure, DKA, starvation, metabolic acidosis, shock) but according to the labs, pt. CO2 got better. If it was r/t something chronic, it wouldn't change that much would it? Another reason it can be low is r/t underfilling the tube when the draw takes place which allows co2 to escape from the serum specimen but that is circumstantial at best and there is nothing validating that happened for it to be 14 one day and 20 5 days later. To top it all off, creatinine is high, sodium is low and potassium is low, all related to excessive vomiting. Pt. was admitted R/T excessive vomiting. But with CO2 levels, they usually rise with excessive vomiting, and my pt's fell. Thoughts?

[Mike R, ADN, BSN, RN]

Someone chime in if I'm wrong but, diarrhea doesn't really affect the CO2 levels as much as the Bicarb levels. CO2 is more of a function of respiration processes. Diarrhea pulls water and electrolytes(including bicarbs) from the vascular space; thus the d(x) of metabolic acidosis. When bicarbs are low, the PH will be low. For the body to maintain PH, the body will use the lungs to blow off CO2 as compensation. The initial draw shows compensation with CO2 in full swing. The second draw shows less compensation (probably the result of medical interventions working towards the goal).

CO2 values can change within minutes simply by changing the breathing pattern and rate. Bicarb values usually takes 24-36 hours as a result of renal function taking longer to kick in.

Look at the big picture. Since he has renal failure it's harder for him to regulate with bicarbs. Lung function is the means for this person to compensate. Since the diarrhea is bringing the PH down, the body is probably compensating with blowing off huge amounts of CO2 with Kussmal breathing that often accompanies DKA.