Nephro - Acid Base - Online MedEd

Question 1

Primary disturbances are…

Answer 1

Resp acidosis/alkalosis

Metabolic acidosis/alkalosis

Question 2

Start with what in acid base disorders?

Answer 2

pH
7.35-7.45
-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)

Question 3

After looking at pH what is the next step?

Answer 3

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

Question 4

How to think of CO2

Answer 4

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

Question 5

Respiratory acidosis differential

Answer 5

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

Question 6

Respiratory alkalosis - differential

Answer 6

Hyperventilation - pain and anxiety; instances of hypoxemia

Question 7

Metabolic alkalosis - what is the next test to get?

Answer 7

Urine chloride!

• 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

Question 8

Contraction alkalosis - what is it?

Answer 8

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

Question 9

Volume responsive metabolic alkalosis occurs in what instances?

Answer 9

Diuretics
Dehydration
Emesis/NG suction
-Urine chloride is low

Question 10

If metabolic alkalosis, but urine chloride is normal

Answer 10

Consider hypertension - hyperaldo states

Question 11

No hypertension in metabolic alkalosis

Answer 11

Gittleman

Darteur

Question 12

So in volume contraction metabolic alkalosis what is the treatment

Answer 12

Treatment is volume repletion

Question 13

With metabolic acidosis… what do you need to assess?

Answer 13

Anion gap

Na-Cl-HCO3

Question 14

Anion gap > 12… what is this?

Answer 14

Anion gap acidosis

Question 15

Anion gap < 12… what is this?

Answer 15

Non-gap

Question 16

Normal albumin will have anion gap of what?

Answer 16

12

Question 17

Anion gap acidosis… what mnemonic to use?

Answer 17

MUDPILES
Look for a compound that is osmotically and acid base active
Methanol, uraemia, DKA, propylene, isopropyl, lactic acid, ethylene glycol, salicylate

Question 18

Non gap metabolic acidosis… what do you want to assess?

Answer 18

Urine anion gap?
Urine Na + Urine Potassium - Urine Chloride
*Different than serum anion gap equation

Question 19

How to divide urine anion gap?

Answer 19

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)

Question 20

What are the steps to look at primary disturbance

Answer 20

Step 1: pH
Step 2: CO2
Step 3: other disturbance?

Question 21

Resp acidosis

Answer 21

Means pH acidemic

Respiratory acid is high

Question 22

Metabolic acidosis

Answer 22

Means pH is acidemic
Respiratory acid is low (CO2 is low)
So metabolic acidosis

Question 23

Resp alkalosis

Answer 23

pH is high

Respiratory acid is low (CO2 is low)

Question 24

Metabolic alkalosis

Answer 24

pH is high

Resp acid is high

Question 25

Always check…

Answer 25

Anion gap

*Doesn’t matter what the primary disturbance is… always check anion gap

Question 26

After determining pH and CO2… what are the next 3 steps?

Answer 26

1) Check anion gap
2) Check: acute or chronic
3) Bicarb appropriate?

Question 27

How do you determine chronicity?

Answer 27

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?

Question 28

What are acute and chronic changes of bicarb in respiratory acidosis and respiratory alkalosis for every dime change in CO2?

Answer 28

Respiratory acidosis… bicarb change 1 (acute), 3 (chronic)
Respiratory alkalosis… bicarb change 2 (acute), 4 (chronic)
*dime change of CO2

Question 29

Is expected bicarb equal to given bicarb? what does this tell you about additional metabolic changes

Answer 29

If too much bicarb/base… then there is coexisting metabolic alkalosis
If too little bicarb… metabolic acidosis

Question 30

Metabolic acidosis - what steps?

Answer 30

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)

Question 31

Metabolic alkalosis means

Answer 31

Aldosterone is up!
No equations needed here
No need to determine another disturbance
-Check anion gap to check for metabolic alkalosis with anion gap metabolic acidosis