UWorld - Renal & Electrolytes

Question 1

What uremic toxins are responsible for platelet dysfunction in chronic renal failure?

Answer 1

Guanidinosuccinic acid

Question 2

How do you correct the platelet dysfunction seen in uremia coagulopathy and how do you assess response to the treatment?

Answer 2

DDAVP releases factor VIII:vWF multimers from endothelial storage sites, increasing platelet aggregation and improving bleeding time. Cryoprecipitate and unconjugated estrogens can also be used.

Question 3

Name 4 causes of hypovolemic hyponatremia

Answer 3

Volume depletion, renal insufficiency, GI loss and renal loss (diuretics). Note that ADH is appropriately increased in these conditions because stimulation due to hypovolemia trumps suppresses due to decreased osmolality. This is why hyponatremia is correct with NS bolus in these conditions.

Question 4

Name 4 causes of euvolemic hyponatremia

Answer 4

SIADH, psychogenic polydipsia, secondary adrenal insufficiency and hypothyroidism. ADH is inappropriately increased in these conditions.

Question 5

Name 3 causes of hypervolemic hyponatremia

Answer 5

CHF, cirrhosis and CKD/nephrotic syndrome. ADH is inappropriately increased in these conditions.

Question 6

What anions present in the serum account for the normal anion gap of 6-12?

Answer 6

Proteins, citrate, phosphate and sulfate

Question 7

Most common causes of anion gap metabolic acidosis?

Answer 7

#1) Lactate
#2) Ketoacids (beta-hydroxy butyrate + acetoacetate)
#3) Methanol/Formaldehyde ingestion
#4) Ethylene glycol ingestion
#5) Salicylate poisoning
#6) Uremia

Remember MUDPILES: methanol, uremia, DKA, paraldehyde, INH or iron, lactic acid, ethylene glycol, salicylates

Question 8

Common causes of non-gap metabolic acidosis?

Answer 8

Diarrhea, RTA, GI fistula, post-hypoventilation, post-gap acidosis

Question 9

Why is NS infusion of 200mL/hr to the point of 100-150mL/hr of urine output first line treatment for hypercalcemia? Why is this better than loop diuretics?

Answer 9

Hypercalcemia causes urinary salt wasting leading to hypovolemia. Hypovolemia impairs Ca excretion and exacerbates the pre-existing hypercalcemia. Giving lots of fluids corrects the hypovolemia and allows for Ca excretion. Loop diuretics exacerbate the hypovolemia, so despite “wasting” Ca, they make the situation worse.

Question 10

How to check for appropriate compensation in a metabolic acidosis? Acute metabolic alkalosis? Acute respiratory acidosis? Acute respiratory alkalosis?

Answer 10

MAc = Winter's formula
MAl = PaCO2 increases by 0.7 for each 1 increase in HCO3
RAc = HCO3 increases by 1 for each 10 increase in PaCO2
RAl = HCO3 decreases by 2 for each 10 decrease in PaCO2

Question 11

Indications for urgent dialysis

Answer 11

Acidosis: pH 6.5 refractory to treatment or symptomatic
Ingestion: alcohols, salicylate, Li, valproate, carbamazepine
Overload: refractory to diuretics
Uremia w/symptoms (encephalopathy, pericarditis, bleeding)

Question 12

What conditions can cause asterixis

Answer 12

Hepatic encephalopathy, renal encephalopathy and hypercapnea

Question 13

Most common cause of nephrotic syndrome in patients with HIV

Answer 13

FSGS. This can occur even when CD4 counts are high and viral load is low.

Question 14

Common causes of crystal-induced AKI

Answer 14

Acyclovir, sulfonamides, methotrexate, ethylene glycol and protease inhibitors. This usually occurs within 24-48 hours of taking the medication.

Question 15

Common drugs that cause AIN?

Answer 15

Beta-lactam antibiotics and PPIs. Note that AIN usually takes place 7-10 days after taking the medication.

Question 16

Reversible causes of urinary incontinence

Answer 16

"DIAPPERS": 
Delirium
Infection: UTI
Atrophic vaginitis/urethritis
Pharm: alpha blockers and diuretics
Psych: depression
Excessive output: CHF & DM
Restricted mobility: surgery
Stool impaction

Question 17

How does aspirin overdose cause a mixed acid base picture?

Answer 17

Salicylates stimulate the medullary respiratory center and cause a respiratory alkalosis. At the same time it stimulates increased production and decreased elimination of ketoacids and lactic acids, resulting in a metabolic acidosis.

Question 18

How does glomerular damage progress in a patient with diabetes?

Answer 18

1) Glomerular hyperfiltration
2) Thickening of the basement membrane
3) Mesangial expansion
4) Nodular sclerosis

ACE-I work to prevent renal damage in diabetics by dilating the efferent arteriole and minimizing glomerular hyperfiltration

Question 19

Next step when the anion gap is markedly elevated and frank uremia is not present?

Answer 19

Calculate the osmolar gap to assess for ethanol, methanol or ethylene glycol intoxication.

1) Calculate serum osmolality = (2Na) + (Glu/18) + (BUN/2.8)
2) Calculate the gap = observed - calculated osmolarity
3) Gap > 10 = ethanol, methanol or ethylene glycol intoxication

Question 20

A patient presents to the ED in acute heart failure, renal failure and ARDS. There is a gap acidosis and osmolar gap is > 10. Urine shows rectangular, enveloped-shaped crystals. What is causing his symptoms?

Answer 20

Ethylene glycol intoxication. The crystals seen are calcium oxalate crystals that precipitate in patients with ethylene glycol poisoning.

Question 21

A patient presents to the ED with snowfield vision and acute pancreatitis. There is a gap acidosis and osmolar gap is > 10. What is causing his symptoms?

Answer 21

Methanol poisoning.

Question 22

Dietary habits that can lead to nephrolithiasis

Answer 22

High protein
High vitamin C intake
High sodium intake
Low calcium (paradoxical effect)
Low fluid intake