Acid-Base Disorders

Acidosis; first we evaluate the primary disorder, and the definitions of the primary disorder. If you think about acid-base balance in a logical stepwise fashion, you may be able to remember it and figure it out. If you don’t do it in a logical stepwise fashion you are almost for sure not going to be able to do it, and even if you do think about it in a logical stepwise fashion, a lot of people have problems with it – like me. So it’s got to be logical and stepwise. So number one, we think of the primary disorder. What is the primary disorder? If there is metabolic acidosis, the pH is low compared to 7.4. If the primary cause is loss of bicarbonate, the lab finding; a low CO2. I make a big differential here between CO2 and of course PCO2. Because PCO2 is the respiratory component, the carbonic acid. If there is a respiratory acidosis – you have again, a low pH – you have increased carbonic acid and that’s an increased PCO2. So contrast these two. If it’s alkalosis the pH is high and metabolic alkalosis is caused by increased bicarbonate or low chlorides, and an increased CO2 is found in your electrolytes. Respiratory, again an increased pH, a low bicarbonate, a low PCO2. This is important to review. This seems simple. You guys have gone over it again and again, but this is important to review and be sure you’ve got cold.

The compensations are likewise important. Remember, you can never overcompensate so you determine the primary changes first. Metabolic acidosis, low CO2. What is the compensation? The compensation is in the other system; increased ventilation, and the result is decreased PCO2. But the primary is an acid pH in the blood and a low CO2. Respiratory acidosis, the primary change, high PCO2. Retained PCO2. The compensation is renal bicarbonate absorption and a high CO2. If you are acidotic and you see these two things, you are going to know that first, this is what would give you the high … the respiratory acidosis. Below the 7.2 type of blood pH. Remember please, that you cannot make a distinction of whether a patient is acidotic or alkalotic unless you have either a venous blood gas or an arterial blood gas that shows a pH. These numbers in and of themselves cannot show you whether the patient is acidotic or alkalotic. Very important to remember…

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