Acid Base Compensations

[UCSBMed1]

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Quick question,

Do they really expect us to memorize the rules for whether adequate compensation has occurred in a acid-base reaction? I understand them, but don't want to memorize for every 0.7 PCO2...

Da*nit! Tell me we don't...

 

[Idiopathic]

Adequate compensation (i.e. pH returning to normal after a chronic acid/base disturbance) theoretically should never happen while the disturbance is still in place. I think they expect you to understand acute problems (i.e. barbiturate overdose=acute respiratory acidosis) vs chronic problems (i.e. renal failure=chronic metabolic acidosis) and understand what the compensatory mechanisms are. There are some to memorize that are mixed (aspirin overdose, COPD on diuretic therapy or something like that, etc.) and these will give you normal pH with abnormal HCO3- and CO2. Remember if those two values are abnormal with a normal pH then it is almost always a mixed disorder and there is not compensation. Otherwise, figuring out the primary disturbance and the proper compensation is usually straightforward.

 

[UCSBMed1]

Adequate compensation (i.e. pH returning to normal after a chronic acid/base disturbance) theoretically should never happen while the disturbance is still in place. I think they expect you to understand acute problems (i.e. barbiturate overdose=acute respiratory acidosis) vs chronic problems (i.e. renal failure=chronic metabolic acidosis) and understand what the compensatory mechanisms are. There are some to memorize that are mixed (aspirin overdose, COPD on diuretic therapy or something like that, etc.) and these will give you normal pH with abnormal HCO3- and CO2. Remember if those two values are abnormal with a normal pH then it is almost always a mixed disorder and there is not compensation. Otherwise, figuring out the primary disturbance and the proper compensation is usually straightforward.

Hey Thanks for the response!

 

[katieb]

I'd at least know Winter's formula.

 

[Idiopathic]

Worthless, IMHO. If you cant get the answer from the clinical presentation or directly from the lab values, then you erred somewhere. If you know Winter's formula (for calculating appropriate A/B responses) the good, but if you dont know it, I dont think there is a call to memorize it. I did not need it on either USMLE or COMLEX and have not seen a realistic Step I review question that required its application.

 

[divinemsm]

Here's a " quick and dirty " that has, thus far in Q-bank anyway, gotten me to the right answer...I have yet to take my actual exam

Respiratory Acidosis: CO2 will be increased, HCO3 will be increased
Metabolic Acidosis: CO2 is unchanged, HCO3 is significantly decreased
Mixed Acidosis: CO2 increased, HCO3 decreased

Respiratory Alkalosis: CO2 decreased, HCO3 decreased
Metabolic Alkalosis: CO2 unchanged, HCO3 significantly increased
Mixed Alkalosis: CO2 decreased, HCO3 increased

maybe this will help if in a bind...good luck !