I need to explain the rationale for two abnormal sets of ABGs for a patient. Both values were taken on his surgery day for a AAA repair (I'm not sure if they were before, during, or after surgery).
Base Excess -1.3
O2 sat 99.8
This appears to be respiratory acidosis judging by the low pH and the high CO2. Why would he be in respiratory acidosis around surgery time (maybe was his resp. system depressed by anesthesia or other meds during surgery?)? Why is his PO2 so incredibly high?
Base Excess -3.5
O2 sat 94.4
So now he's in acidosis from the low pH, but every other value except the PO2 is normal. Does hypoxemia cause acidosis? If so, which kind of acidosis is it?
Thanks for any help you can provide!
You're right, lactic acidosis is an example of metabolic acidosis resulting from anaerobic metabolism causing release of lactic acid from conditions such as sepsis, drug ingestions, etc. But what I was trying to explain is that when we look at ABG's, it is the pCO2 and HCO3 we look at to determine the underlying acid-base etiology, not the pO2.
I would like to add that in lactic acidosis, we do look at the ABG but only in terms of knowing that the pH is low and the base deficit is high. As your example shows, your pO2 on the ABG was normal in your patient while the pO2 on your venous gas is too high (identical to ABG pO2) since the body is not able to extract oxygen in the tissues. Lactic acidosis is not diagnosed with the ABG alone but with checking for mixed venous gas, anion gap, and a serum lactate level.
Last edit by juan de la cruz on Feb 28, '07
Quote from pinoyNP
Lactic acidosis is not diagnosed with the ABG alone but with checking for mixed venous gas, anion gap, and a serum lactate level.
I know this, but thank you for clarifying that oxygen does play a very inportmant role in pH. A lactate level would be drawn of course,but we would know that it was lactic acidosis just by doing a venous gas with the p02 being virtually the same as the abg.
Last edit by loafin' on Feb 28, '07