Originally posted by Tenesma
you need to understand how base deficit and base excess is calculated... yes, that is right...
BE = (1 - 0.014 x Hgb)[(calculatedHCO3 - 24.8) + (1.43 x Hgb + 7.7)(pH - 7.40)]
if the HGB isn't measured the lab will assume that HGB=15 (which in most patients, especially ones needing ABGs, is very inaccurate)
See, this is where people get all confused by the formulas. Yes, if Hgb is not measured simultaneously, BE calculations will be inaccurate. But, the key question is "how inaccurate?" Even if the patient's Hgb is 7 and the machine operator assumes Hgb 15 (a gross overestimate), the margin of error is going to be about 10-14%, which is nothing. What, the "real" base excess is going to be 3.3 instead of 3? Who cares? The margin of error in the formula within wide variations of Hgb is minimal.
so do you need BE or HCO3 to know that somebody has a metabolic acidosis... no, you can figure everything out based on pH and PCO2
See this is what happens when you respond to someone without paying attention to exactly what they said in the first place. Read my sentence again. I never said you can't determine the "presence" of a metabolic disorder by pH and PCO2 only, but I said you can't determine the"severity" of the metabolic component. Also, you still can't determine even the "presence" of triple acid-base disorders anyway.
are also right that there are indications for bicarbonate infusions... but those aren't dosed based on base deficits... but since you are adamant about your point, please tell me how much bicarb to give if the base deficit is 5 or if the base deficit is 10???
It's use is similar to the one used for sodium replenishement in hyponatremia.
The total body base deficit is:
BD x 0.5 x kg = mEq of HCO3
However, you don't correct the entire base deficit. For replenishment, you only give BD x 0.3 x kg. Of course you don't HAVE to use base deficit for calculating how much to give. There are other ways too.
A good book for anyone interested in the topic is: Rose - Clinical Physiology of Acid-Base and Electrolyte Disorders. It's long ~900 pages, but I read the old edition way back in medical school. It's amazing. It gives a lot of real-life clinical examples. I got to wean from this discussion board for a few days or weeks. Too much time spent here.