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NBME 20 Answers

nbme20/Block 1/Question#18

A 36-year-old man comes to the physician because he ...

Urine output: increased; Urine potassium: increased

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 +7  upvote downvote
submitted by hayayah(525),

The tubes are catheters put in for urine to flow into a bag. So urine output is going to increase. The patient is also hyperkalemic. Aldosterone responds to hyperkalemia by increasing K+ excretion.

Hyperkalemia will stimulate aldosterone secretion even if renin is suppressed due to his hypertension. Although Na+ will be reabsorbed, this will be transient (should resolve once the potassium levels normalized) and since his urine output will most likely return to normal, his blood pressure should also normalize.

charcot_bouchard  Postobstructive diuresis Postobstructive diuresis is a polyuric state in which copious amounts of salt and water are eliminated after the relief of a urinary tract obstruction. The incidence of POD is unclear but estimates suggest 0.5% to 52% of patients will experience POD after relief of obstruction.10 It generally occurs after relieving BOO, bilateral ureteric obstruction, or unilateral ureteric obstruction in a solitary kidney.11 Diuresis is a normal physiologic response to help eliminate excess volume and solutes accumulated during the prolonged obstruction. In most patients, the diuresis will resolve once the kidneys normalize the volume and solute status and homeostasis is achieved. Some patients will continue to eliminate salt and water even after homeostasis has been reached, referred to as pathologic POD. These patients are at risk of severe dehydration, electrolyte imbalances, hypovolemic shock, and even death if fluid and electrolyte replacement is not initiated.9 +4  

 +1  upvote downvote
submitted by step1soon(20),

In postobstructive diuresis the Urine is usually hypotonic with large amounts of sodium chloride, potassium, phosphate and magnesium [3] Urine Output > 125 - 200mL/hour after relief of obstruction for at least 3 consecutive hours[4] Urine Osmolarity > 250mosm/kg [5]