DSA Acid Base Compensation Flashcards
What are two rules regarding compensation?
- Compensation never gets back to normal
- Compensation must occur through the other system: thus a respiratory disturbance must be fixed with a metabolic compensation
How does our metabolic system compensate for respiratory disturbances?
DCT and CD cells in the distal convulated tubule can excrete and reabsorb H+ or bicarb when needed.
Thus; if we have a respitory acidosis, how will our metabolic system compensate?
DCT/ CD cells are going to excrete H+ ions and reabsorb bicarb to increase our pH.
Thus, we see an increase in bicarb levels.
How does our metabolic system compensate for respiratory alkalosis?
DCT/CD cells are going to excrete bicarb into the urine and reabsorb H+ ions, to decrease our pH.
–> As a result, you will see decreases in plasma bicarb levels.
Steps in determining type of respiratory problems
- Acidosis or alkalosis?
- Respiratory or metabolic?
- Is the body compensating for the problem?
- If yes, problem is chronic that the bodies are dealing with.
- If no, the problem is acute.
For respiratory acidosis, to check if acute or chronic
If the problem is acute: Expected [bicarb]= 24 + ((PaCO2-40)/10)
If the problem is chronic: Expected [bicarb]=24+ 4 ((PaCO2-40/10)
–in both cases, if we have a respiratory acidosis, we expect our bicarb to increase.
For respiratory alkalosis, to check if acute or chronic
- Acute*: Expected [bicarb]= 24 – 2 ((40-PaCO2)/10)
- Chronic*: Expected [bicarb]= 24-5 ((40-PaCO2/10)
–in both cases, if we have a respiratory alkalosis, we expect our bicarb to decrease.
If we have increase H+ in the blood (decreased pH), how can we fix?
Hyperventilation–> blow out CO2 and increase pH.
Decreased H+ in the blood= increase pH.
How can we fix?
Hypoventilate–> retain CO2 and decrease pH.
If metabolic system is compromised, __________ tries to fix the pH.
Respiratory tract
Metabolic acidosis with respiratory compensation (_________)
Hyperventilation
Metabolic alkalosis with respiratory compensation (________)
Hypoventilation
If we have metabolic acidosis, how do we check is the respiratory compensation is adequate?
Expected PaCO2= (1.5[HCO3] + 8) +/- 2
Why do we ask if respiratory response is adequate and not acute/chronic?
- Because the respiratory response will be very quick and occur before the condition can be considered chronic.
- The respiratory system can only influence a small part of the total HCO3, so it never gets the pH as close to normal as one would expect.
If we determine that the problem is a metabolic acidosis, we have to calculate the anion gap. WHY?
Because we can use up our bicarb by making an acid we hadn’t planned on: lactic acids, ketoacids, etc.
Anion gap is based on the rule that the + and – should always balance themselves out.
What is the anion gap?
Should be based on the one rule: + and - should always balance themselves out.
Anion gap= Na- (Cl+ HCO3)
If I am making an acid that is not measured via tests, HCO3- will decreae because it Is acting as a buffer for the acid. Thus, an anion gap occurs. The positives and negatives will not balance themselves out because we have lost the HCO3.
Normal anion gap
< or equal to 12.
What does an elevated anion gap mean?
unmeasured chemicals are present in the blood.
Example: in diabetic ketoacidosis, starvation or alcoholic ketoacidosis, lactic acids, salicylates (ASN)
Thus, these cause metabolic acidosis.
If we have metabolic alkalosis, how can we check if respiratory compensation is adequate?
Change in PaCO2= (0.5 to 1.0) * change in bicarb
In this case, the change is an increase in CO2
