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?
Discussion of interesting or befuddling cases related to pulmonary and critical care medicine.
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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
BTW, no protein was done, but his serum albumin was less than 1.
I agree with Doug. The low albumin will lower your AG but will not explain the incongruencies.
Too much heparin in the ABG sample could falsely make the sample acidotic
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...
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.
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