Renal Acidosis

Question 1

What are buffers?

Answer 1

Weak acids

Question 2

What organ has the largest buffering capacity?

Answer 2

Bone

Question 3

What is the most important buffer in the ECF?

Answer 3

Bicarbonate

Question 4

What is the purpose of buffering?

Answer 4

To prevent major shifts in hydrogen ions

Question 5

What ions mediates intracellular buffering?

Answer 5

Hemoglobin, phosphate, protein

Question 6

What is the chronic effect of acidosis on bone?

Answer 6

Osteoporosis

Question 7

What are the two types of acids contribute to your acid load?

Answer 7

1. Carbonic

2. Non-carbonic

Question 8

What type of acid created by the body will become volatile (i.e. excreted by the lungs)

Answer 8

Carbonic acids

Question 9

Metabolism of what macro-nutrients creates carbonic acids?

Answer 9

Fat and Carbohydrate metabolism

Question 10

How are carbonic acids excreted?

Answer 10

Eliminated by the lungs after conversion to CO2

Question 11

Metabolism of what macronutrients leads to non-carbonic acid formation?

Answer 11

Protein, ingested sulfate, phosphate, inorganic acid

Question 12

How are non-carbonic acids excreted?

Answer 12

Non-volatile therefore excreted via kidneys

Question 13

Patient presents with pH 7.25, pCO2 30mmHg, what type of acidosis?

Answer 13

Metabolic acidosis

Question 14

How do you calculate the anion gap?

Answer 14

Na + K - Cl - HCO3 = 12-14 normally

Question 15

Why is the anion gap not zero?

Answer 15

Albumin is an anion that is not measured

Question 16

What is the name of metabolic acidosis with an anion gap of <14?

Answer 16

Carbonic/volatile acid = Non-Anion Gap Metabolic Acidosis (NAGMA)

Question 17

What is the name of metabolic acidosis with anion gap of >14?

Answer 17

Non-Volatile/Non-Carbonic acid = Wide Anion Gap Metabolic Acidosis (WAGMA)

Question 18

What do you do with a patient with a wide anion gap?

Answer 18

Look for anions - ingested or intrinsic

Question 19

What is the differential for a WAGMA?

Answer 19

MUDPILES
M - methanol/metformin
U - uremia
D - DKA
P - paraldehyde
I - iron, infection, isoniazid, isopropyl alchohol
L - lactate
E - Ethylene glycol
S - salicylates

Question 20

What do you do with a patient with a normal anion gap acidosis?

Answer 20

Think…

1. Bicarbonate loss
2. Volatile acid gain
3. Unable to make bicarbonate

Question 21

How is bicarbonate reabsorbed?

Answer 21

90% in proximal tubule, 10% in thick ascending LoH. (follows Na reabsorption

Question 22

How does the kidney excrete the necessary 50-100 mEq of H+/day?

Answer 22

Energy dependent ATPase and hiding the proton in diet-derived titratable acid

Question 23

What is the purpose of glutamine metabolism in the context of acid/base balance

Answer 23

Formation of two NH4+ and two HCO3- (bicarb formation for buffering)

Question 24

What are the non-renal causes of bicarbonate loss?

Answer 24

Diarrhea
Post hypocapnea (kidneys overcorrecting)
Drugs (acetazolamide=carbonic anhydrase i)

Question 25

What are the non-renal causes of acid retention/reabsorption?

Answer 25

``` Urinary diversions (i.e. to colon) Drugs (spironolactone - blocks acid secretion) ```

Question 26

What are the non-renal causes of inability to make ammonium or bicarb?

Answer 26

Total parenteral nutrition

Question 27

Which amino acid is needed to create bicarb?

Answer 27

Glutamine

Question 28

How can the presence/absence of NH4+ in the urine be diagnostic?

Answer 28

Determines the nature of acid/base problem * proximal bicarb uptake problem=NH4+ in urine * distal H+ secretion problem=no NH4+ in urine * problem making/transporting NH4+ = no NH4+ in urine, corrected with exogenous titratable acid

Question 29

When would ammonium be present in the urine?

Answer 29

When the body needs to excrete acid

Question 30

How are urine ammonium levels measured?

Answer 30

Charge balance... NH4+ = Cl - Na - K NH4+ = 0 to 40

Question 31

Define an osmole

Answer 31

Discrete particles in solution that cause water movement to balance gradients. i.e. NaCl - 2 osmoles, CaCl2 - 3 osmoles

Question 32

How do you measure urine osmolar gap?

Answer 32

Measured Osm - calculated Osm

Question 33

What is the formula for the calculated urine osmolality?

Answer 33

2Na + 2K + 2(NH4) + glucose + urea

Question 34

How do you measure NH4+ from the urine osmolar gap?

Answer 34

NH4 = (mOsm - 2Na - 2K - glucose - urea) / 2

Question 35

When is the osmolar gap inaccurate?

Answer 35

When patient has uncharged osmoles like alcohol in the urine

Question 36

Which NAGMA presents with urine NH4?

Answer 36

Bicarb loss

Question 37

Which NAGMAs present with no urine NH4?

Answer 37

H+ retention - urine pH stable giving titratable acid | Can't make NH4/HCO3 - urine pH drops with titratable acid