My Preceptor has stumped me!

[Heatherheartsou, BSN, RN]

I am a nurse extern in the emergency room and my preceptor asked, what is the significance of CO2 in a diabetic patient. We were doing blood gases on a patient. I knew all about the HCO3 and ketoacidosis.... but I have been unable to find ANYTHING on CO2. Anyone know anything about this. I am suppossed to tell her what I found when I return, but I am truly stumped. I looked in my textbooks and googled it. Anyway, I just need to be steered in the right direction. Thanks.

[traumaRUs, MSN, APRN]

The lower the CO2, the more acidotic your pt is. For instance, I work with renal pts who are frequently acidotic.

[CritterLover, BSN, RN]

are you talking about co2 on the blood gas, or on the chemistry panel?

the co2 on the chemistry panel closely correlates with the hco3 on the blood gas

(goes back to chemistry: h2o + co2 h+ + hco3-; which state is favored depends on factors like ph).

the co2 on the blood gas (which is in different units than the co2 on the chemistry panel, so don't expect them to match) should also be low if the patient is in metabolic acidosis.

you know that ketoacidosis causes a patient to drop their ph -- a metabolic acidosis. well, in order to compensate, you start to blow off co2, in your body's attempt to normalize the ph -- which is why they tend to breathe so fast and so deep.

this is significant for two reasons -- first, the lower the co2, the worse the acidosis, and the harder the body is working to normalize the ph.

second, because breathing that fast/deep is hard work -- and eventually, they will get tired. as their respiratory rate starts to fall, they lose that ability to compensate, and their ph will rapidly fall as they rapidly decompensate. they need to be intubated prior to reaching that point, or they are at very high risk for respiratory (followed quickly by cardiac) arrest.

[Daytonite, BSN, RN]

from page 105, mosby's diagnostic and laboratory test reference, 4th edition, by kathleen deska pagana and timothy james pagana, 1999. . ."the pco2 is a measurement of ventilation capability. the faster and more deeply one breathes, the more co2 is blown off, and pco2 levels drop. . .the co2 level and the ph are inversely proportional. . .the pco2 is elevated in primary respiratory acidosis. because the lungs compensate for primary metabolic acid-base derangements, pco2 levels are affected by metabolic disturbances as well. in metabolic acidosis the lungs attempt to compensate by "blowing off" co2 to raise ph."

[Heatherheartsou, BSN, RN]

Thanks so much. I believe I do remember discussing Kussmaul's respirations in lecture. I just needed to put the two together. You all are great!