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#1
07-08-2010
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Acid Base Disorders in USMLE Step 1

Do we need to know the exact calculations for the compensations of all the disorders?
 The above post was thanked by: CHAKRAM (12-08-2011)

#2
07-09-2010
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,317 Threads: 170 Thanked 4,880 Times in 1,808 Posts Reputation: 4933
What do you mean

Do you mean the formulas that let you calculate how much pCO2 should decrease in the face of how much bicarbonate is elevated and stuff like that.
#3
07-10-2010
 USMLE Forums Addict Steps History: Not yet Posts: 161 Threads: 60 Thanked 23 Times in 19 Posts Reputation: 33

yeah i mean those

#4
07-10-2010
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,317 Threads: 170 Thanked 4,880 Times in 1,808 Posts Reputation: 4933
Perhaps on the Winter's Formula

No, I don't think you need to know the exact equations and numbers to calculate the various changes in an acid base disorder.

It's important however that you know (by heart) the normal values of the PH, CO2, and Bicarb so that then you can judge what is the problem.

See the PH first then look at the CO2 then see the bicarb.

Do practice questions as much as you can. This is a very high yield topic.

There's one exception (I think) which is the Winter's formula that you need to memorize.

Winter's Formula

Expected pCO2 = 1.5 X HCO3- + 8
this is to measure the adequacy of respiratory compensation in cases of metabolic acidosis (specially in DKA cases).

Example:
Patient with DKA and his bicarb is only 8, then his pCO2 should be 20 if it's higher than that then he's not adequately compensating (respiratory fatigue or ensuing coma) then you need to think of assisting his ventilation.
 The above post was thanked by: alaric (03-17-2013), Androide89 (07-10-2010), CHAKRAM (12-08-2011), GAUTAMCHAND15 (10-01-2015), khan89 (10-31-2014), LatinGeorge (12-07-2011), Linc (08-16-2015), Master shifu (02-25-2012), voicesinmyhead (11-04-2013)
#5
07-10-2010
 USMLE Forums Addict Steps History: Not yet Posts: 161 Threads: 60 Thanked 23 Times in 19 Posts Reputation: 33

Awesome thanks a lot, btw where did u get winter's formula is that in FA?
#6
07-10-2010
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,317 Threads: 170 Thanked 4,880 Times in 1,808 Posts Reputation: 4933
I just know it

Am not sure if it available in FA or any other book.
I just know this formula by heart and I remember there were practice questions that needed it to solve the problem.
#7
07-10-2010
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 187 Threads: 4 Thanked 368 Times in 121 Posts Reputation: 398

Yeap, Winter's formula, as well as the rest of compensations (which are unmemorizable, btw!) are all included in FA.
#8
07-10-2010
 USMLE Forums Addict Steps History: Not yet Posts: 161 Threads: 60 Thanked 23 Times in 19 Posts Reputation: 33

Quote:
 Originally Posted by ath.pantelis Yeap, Winter's formula, as well as the rest of compensations (which are unmemorizable, btw!) are all included in FA.
yah they are unmemorizable hopfully none show up on the exam!
#9
12-07-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 653 Threads: 47 Thanked 409 Times in 249 Posts Reputation: 419

i was reading goljan, and i think FA makes it very easy to understand. Plus you need to read kaplans physiology to get davenport and add it to FA.
#10
08-16-2015
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 20 Threads: 3 Thanked 11 Times in 5 Posts Reputation: 21
Winters Formula

PaCO2 = (1.5 x Bicarb)+8 +/- 2

 Tags Electrolytes-, Physiology-

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