Wednesday, August 09, 2006

Acid Base

The chem-7 and the gas were both drawn within 22 minutes of each other in this 71 year old intubated man with sepsis and ARDS:

7.08/24/226 on fio2 of 75%

Na 145
k 5.2
Cl- 114
HCO3 28
BUN 42
Cr 0.5

What is the acid base disturbance?

7 comments - CLICK HERE to read & add your own!:

Arenberg said...

The numbers do not fit the H-H equation. You can't have a PCO2 of 24 (hyperventilation) and a bicarb of 28 on the side of alkalosis) and have a pH that low. pH should be ~7.55 with those two numbers. THis suggests to me there is a lab error. The AG is low, at 3, and I wonder if there isn't a reason for that, like a paraprotein?
What else would cause the instrument to read a falsely low pH with no anion gap?

Jennings said...

I agree; if you do the H-H equation, the calculated bicarb should be 7. I agree that the only interpretation I can think of is that this is a lab error. However, a few days earlier he had a similar gas where the measured bicarb was above 24 and the calculated was again low.
I wonder what factors would contribute to the machione measuring this incorrectly. I think that the way they measure bicarb in a chem-7 is to add a strong acid thuis converting the bicarb to CO2 and water and then the machine measures the CO2, but this would give you an error in the other direction...
BTW, a good online calulator for hend-hasselbach equation: http://medcalc3000.com/HendersonHasselbach.htm

Jennings said...

BTW, no protein was done, but his serum albumin was less than 1.

Baleeiro said...

I agree with Doug. The low albumin will lower your AG but will not explain the incongruencies.

Suresh said...

Too much heparin in the ABG sample could falsely make the sample acidotic

Jennings said...

That's interesting, because the patient was indeed on heparin. Furthermore, when the gas was repeat the pH was about 7.32 so maybe that one was drawn from the peripheral line...

Anonymous said...

Just a clarification - it's the quantity of heparin(in the syringe) and blood sample drawn that could alter the ABG. Heparinisation of the patient should not make any difference.