Let’s talk about rapid A.B.G. analysis. Just to clarify, I’m talking about arterial blood gases, not the religious rap group “Adopted By Grace” I just discovered existing by googling the phrase “ABG”.
I tend to use Winter’s Formula for analyzing metabolic acidosis: it’s generally simple-enough math I can easily do in my head. To review, Winter’s Formula is used to predict the PaCO2 which should result if there is appropriate respiratory compensation for a metabolic acidosis:
If the actual measured PaCO2 is lower than predicted, there is a concomitant respiratory alkalosis; if it is higher than predicted there is a concomitant respiratory acidosis.
SIMPLIFIED WINTER’S FORMULA:
predicted PaCO2 = [HCO3-] + 15. This apparently works for PaCO2 concentrations between 10-40.
There’s also something called:
THE THUMB RULE:
Put your thumb over the first digit of the pH on the ABG. The PaCO2 should be the last two digits. For instance, if the pH is 7.30, then the PaCO2 should be about 30mmHg; if the pH is 7.15 then the PaCO2 should be about 15mmHg, etc.
These are very simplified (and personally, I don’t think it’s that mentally strenuous to go with the more precise Winter’s Formula), but potentially handy when rapid clinical decision-making is necessary (e.g., perhaps a resident giving you ABG results in the middle of the night).