Flashcards in Nephro - Acid Base - Online MedEd Deck (31):
Primary disturbances are...
Start with what in acid base disorders?
-If pH is not 7.4 = abnormal!
<7.4 = acidemia
>77.4 = alkalemia
-Notice it is "emia" not "osis" (emia refers to disorders of blood)
After looking at pH what is the next step?
Look at CO2, normal CO2 is 40
-If acidemic --> AND too much CO2 --> resp acidosis
-If acidemic --> AND too little CO2 --> blowing off CO2 --> so metabolic acidosis
-If alkalemic --> AND too little CO2 --> resp alkalosis
-If alkalemic --> AND too much CO2 --> metabolic alkalosis
*Think of CO2 as respiratory acid
How to think of CO2
As respiratory acid
-So if CO2 is too much is acidosis --> must be respiratory acidosis
-So if CO2 is too little in alkalosis --> must be respiratory alkalosis
Respiratory acidosis differential
Hypoventilation - opiate overdose (RR too low), asthma/COPD/air trapping, decreased muscular strength (i.e. long-term ventilation), sleep apnea
-If respiratory acidosis - just need to find a cause, no need to find more cause
Respiratory alkalosis - differential
Hyperventilation - pain and anxiety; instances of hypoxemia
Metabolic alkalosis - what is the next test to get?
-Is person volume responsive? or not?
-If person is volume down, RAS activated, aldosterone grabs Na from collecting duct, makes a concentration gradient, so that water is absorbed by aquaporins
-Na brings Cl
-So when volume down, kidneys hold NaCl
-So little urine Cl if volume responsive
-Volume responsive metabolic alkalosis = contraction alkalosis = urine chloride is low
Contraction alkalosis - what is it?
Volume responsive metabolic alkalosis
-Urine chloride will be low in urine, as retained in blood stream to bring in Na when patient is volume down
Urine chloride <10
Volume responsive metabolic alkalosis occurs in what instances?
-Urine chloride is low
If metabolic alkalosis, but urine chloride is normal
Consider hypertension - hyperaldo states
No hypertension in metabolic alkalosis
So in volume contraction metabolic alkalosis what is the treatment
Treatment is volume repletion
With metabolic acidosis... what do you need to assess?
Anion gap > 12... what is this?
Anion gap acidosis
Anion gap < 12... what is this?
Normal albumin will have anion gap of what?
Anion gap acidosis... what mnemonic to use?
Look for a compound that is osmotically and acid base active
Methanol, uraemia, DKA, propylene, isopropyl, lactic acid, ethylene glycol, salicylate
Non gap metabolic acidosis... what do you want to assess?
Urine anion gap?
Urine Na + Urine Potassium - Urine Chloride
*Different than serum anion gap equation
How to divide urine anion gap?
Positive urine anion gap: positively renal tubular acidosis
Negative urine anion gap: diarrhea
*If lose volume will get metabolic alkalosis
But diarrhea loses bicarb as well... so get metabolic acidosis (not alkalosis)
What are the steps to look at primary disturbance
Step 1: pH
Step 2: CO2
Step 3: other disturbance?
Means pH acidemic
Respiratory acid is high
Means pH is acidemic
Respiratory acid is low (CO2 is low)
So metabolic acidosis
pH is high
Respiratory acid is low (CO2 is low)
pH is high
Resp acid is high
*Doesn't matter what the primary disturbance is... always check anion gap
After determining pH and CO2... what are the next 3 steps?
1) Check anion gap
2) Check: acute or chronic
3) Bicarb appropriate?
How do you determine chronicity?
10 points of CO2 (dime change)... pH will change by 0.08 if acute and 0.4 if chronic
1) What is pH and CO2
2) Calculate change in pH from 7.4
3) Then determine if acute or chronic
4) This will help to see if bicarb is appropriate?
What are acute and chronic changes of bicarb in respiratory acidosis and respiratory alkalosis for every dime change in CO2?
Respiratory acidosis... bicarb change 1 (acute), 3 (chronic)
Respiratory alkalosis... bicarb change 2 (acute), 4 (chronic)
*dime change of CO2
Is expected bicarb equal to given bicarb? what does this tell you about additional metabolic changes
If too much bicarb/base... then there is coexisting metabolic alkalosis
If too little bicarb... metabolic acidosis
Metabolic acidosis - what steps?
pH is low
CO2 is low
Step 3? Other there are other problems.
3a. Calculate anion gap (Na-Cl-HCO3). Normal anion gap is 12 (normal anion gap is albumin x 3)
3b. pCO2 appropriate? Winter's formula = 1.5xbicarb + 8 (+/- 2)
If given CO2 is greater than expected (Winter's)... so too many respiratory acids = also have respiratory acidosis
If given CO2 is less than expected... then too few respiratory acids = respiratory alkalosis
-However, if CO2 can be normal so no respiratory disturbance
3c. Bicarb normal? -Can use delta-delta
Use add back method.
-Basically determine anion gap and calculate from normal anion gap
-If H+ which is HCO3 is more than 24 (normal bicarb) this is alkalosis, <24 is metabolic acidosis (nongap)