I had a different thought process to answer this question that might be worth mentioning.
The aldo reasoning is def true as well, stimulus for aldo is hyperkalemia. Costanzo teaches this well, you can also reference BRS physiology 166-167
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]
https://wikem.org/wiki/Post-obstructive_diuresis
submitted by โhayayah(1212)
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 increasingย 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.