Renal/ Acid-Base

Question 1

What is FENa and what can it help you determine?

Answer 1

Fractional excretion of sodium; This calculation is widely used to help differentiate prerenal disease (decreased renal perfusion) from acute tubular necrosis as the cause of acute kidney injury.
(UpToDate)

Question 2

In general, a FENa below 1 percent suggests…

In comparison, a value between 1 and 2 percent may be seen with either disorder, while a value above 2 percent…

Answer 2

…prerenal disease, where the reabsorption of almost all of the filtered sodium represents an appropriate response to decreased renal perfusion.

usually indicates ATN.
(UpToDate)

Question 3

What are the causes of anion gap metabolic acidosis?

Answer 3

Think MUDPILES:

Methanol
Uremia
Diabetic ketoacidosis 
Paraldehyde
Iron/ isoniazide 
Lactic acidosis
Ethylene glycol/ ethanol
Salicylates

Question 4

What are the causes of non-anion gap metabolic acidosis?

Answer 4

Diarrhea
Renal tubular acidosis, esp type 1
Carbonic anhydrase inhibitors (ex: acetazolamide)
Addison’s disease

Question 5

What is Winter’s formula used for?

Answer 5

To calculate the expected pCO2 compensation in a purely metabolic state of acidosis.

[MDCalc app]

Question 6

What is Winter’s formula?

Answer 6

expected pCO2 = 1.5 * HCO3- + 8 +/- 2

[MDCalc app]

Question 7

The symptoms of dialysis disequilibrium syndrome are caused by water movement into the brain, leading to ________ ______. Two theories have been proposed to explain why this occurs: a reverse osmotic shift induced by urea removal and a fall in cerebral intracellular pH.

Reverse osmotic shift — Hemodialysis rapidly removes small solutes such as urea, particularly in patients who have marked azotemia. The reduction in blood urea nitrogen (BUN) lowers the ______ __________, thereby creating a transient osmotic gradient that promotes water movement into the cells. In the brain, this water shift produces cerebral edema and a variable degree of acute neurologic dysfunction.

Answer 7

cerebral edema

plasma osmolality

[From UpToDate: “Dialysis disequilibrium syndrome”]

Question 8

Which types of RTA cause hypokalemia?

Answer 8

Classic distal (type 1) 
Proximal (type 2) 

(From “Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance”)

Question 9

What types of RTA cause hyperkalemia?

Answer 9

Voltage-dependent RTA
Hypoaldosteronism (type 4)

(From “Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance”)

Question 10

What is type I RTA caused by?

Answer 10

Defects in distal hydrogen ion excretion (a. k. a. impaired distal acidification)

(From “Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance”)

Question 11

What is type 2 (proximal) RTA caused by?

Answer 11

Defects that reduce proximal HCO3 reabsorption.

From “Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance”

Question 12

What is the cause of type 4 RTA (hypoaldosteronism)?

Answer 12

Decreased aldosterone secretion or aldosterone resistance.

From “Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance”

Question 13

In a patient undergoing serial urethral dilations, what might you see in the patient’s urinalysis?

Answer 13

WBCs and leukocyte esterase (as well as RBCs)

From renal rotation with Dr. Akoum