Acid/ Base: Quick and Dirty

Acid/Base problems can be really confusing. But, I am going to break it down for you. It will be quick and dirty.

Step 1. Figure out what you have. You know the basics. Metabolic Acidose, Metabolic Alkalosis, Respiratory Acidosis, Respiratory Alkalosis.

Step 2. Based on what you have, you have to do a few simple calculations. Here we go:

Metabolic Acidosis

1. Check the Anion Gap Na + (Cl + Bicarb)
If it is high, check the osmolality (Ya know, that formula you never remember: 2Na + Glucose/18 + BUN/2.8)

Then do calculated osm - measured osm, if it is > 20, then you got one of the ethalene glycol (calcium oxalate stones, woods lamp urine), methanols (oh MY eyes!), isopropyl alcohol (nailpolish remover breath), lactic acidosis or ketoacidosis- start fomepazole if you don't have a good history until you get lab results back

If it is high, also check the stupid delta AG/delta Bicarb gap to look for another "hidden" abnormality

If the patient has a ketoacidosis the ratio of the change in the AG and change in bicarb is usually 1:1, so if you take the change in the AG/1 and the value is less than the actual change in the bicarb (or the actual bicarb is higher), then you have a metabolic alkalosis along with the metabolic acidosis. If it the actual bicarb is lower, than you have a non-gap metabolic acidosis along with the primary disorder

If the patient has a ketoacidosis, the ratio of the change is 1:1.5, so if you take the AG/1.5 and if the value is less than the actual bicarb (or the actual bicarb is higher), then you have a hidden metabolic alkalosis. If the actual bicarb is lower, then you have a NG metabolic acidosis, too!

Another way to look at is Delta AG/Delta Bicarb > 1 -metabolic alkalosis, <1, style="COLOR: rgb(255,204,204)">2. Check if the lungs are working correctly
Winters formula: PCO2= 1.5 (Bicarb) + 8
If the measured PCO2 is higher than expected- respiratory acidosis
If the measured PCO2 is lower than expected- respiratory alkalosis

Metabolic Alkalosis

1. Check to see if the lungs are working
PCO2= 40 + 0.7 (HCO3- 24)
If the measured PCO2 is higher than expected- respiratory acidosis
If the measured PCO2 is lower than expected- respiratory alkalosis

2. Check the Urine Cl
If it is less than 10, saline sensitive, give fluids
If it is greater than 10, it is not saline sensitive and probably mineralocorticoid excess (usually hypertensive)

3. Check the AG and if it is high- go through the steps under the section of metabolic acidosis to make sure you don't have another disorder

4. Check the Delta/Delta gap if the AG is high and go through the process above

Respiratory Acidosis

Acute- the bicarb increases by 1 for every 10 the PCO2 is above 40, the pH decreases by 0.4 for each change of 10

Chronic- the bicarb increases by 3 for every 10 the PCO2 is above 40, the pH decreases by 0.8 for each change of 10

Respiratory Alkalosis

Acute- the bicarb decreases by 1 for every 10 the PCO2 is below 40, the pH increases by 0.4 for each change of 10

Chronic- the bicarb decreases by 5 for every 10 the PCO2 is below 40, the pH increases by 0.8 for each change of 10

Helpful Websites-
Acid Base Online Tutorial