Acid-Base Respiratory Compensation for Metabolic Disturbances

Question 1

What are the two rules of acid/base compensation?

Answer 1

1. The compensation will never get me back exactly to
   normal.
2. The compensation must be made by the other system.

Question 2

If there is increased H+ in the blood (a decreased pH), what is the response?

Answer 2

I will increase my ventilation and blow off more CO2. This will reduce my PaCO2, and bring my pHa back up.

Question 3

If there is decreased H+ in the blood (an increased pH), what is the response?

Answer 3

I will decrease my ventilation and retain more CO2. This will increase my PaCO2, and bring my pHa back down.

Question 4

After we have determined what the acid/base disturbance is, i.e. respiratory or metabolic, what comes next?

Answer 4

We have to decide if the compensation is adequate by the other system. For example, if respiratory comp. is adequate in a metabolic acidosis, the expected PaCO2 = (1.5[HCO3-] +8) +/- 2

Question 5

What do we need to remember to do any time we find a metabolic acidosis? Why?

Answer 5

Calculate the anion gap. Because there are many sources of metabolic acids, ketoacids, lactic acids, etc.

Anion gap = [Na] - ([Cl] + [HCO3]); normal: = 12
* positives and negatives should always balance out
unless an acid is using up my HCO3-

Question 6

What does an elevated anion gap tell us?

Answer 6

There are unmeasured chemicals present. 
-Mnemonic: MUDPILES
Methanol
Uremia
Diabetic ketoacids, alcoholic ketoacids
Paraldehyde
Isoniazid or iron
Lactic acids
Ethylene glycol or ethanol
Salicylates (aspirin)

Question 7

What equation do we use in a metabolic alkalosis, to see if respiratory comp. is adequate?

Answer 7

PaCO2 = (0.5 to 1.0)*HCO3

Question 8

What can we do to estimate blood osmolarity?

Answer 8

Osmolarity = (2x serum Na) + (BUN/2.8) + (glucose/18); normal: 290 mOsm; tightly regulated