One of the effects of sympathectomy is dilatation of the blood vessels (Vaso Dilatation). Because of that there is increased blood flow to the kidneys and as a result more urine output ensues. This particular effect is self limiting due to the fact that the vessels, that have autonomic (self regulating) will get back to their normal size after a short time. Essentially this issue is only temporary (days not weeks). The same can happen to patients who suffer from severe headaches (migraine headaches).
One of the theories connects migraine headaches with narrowing (vaso spasm) of the vessels in the head area. The sympathectomy, especially ETS will cause dilatation of those vessels. Patients describe reduction in the quantity, frequency and intensity of the headaches and allow them to reduce the amount of specific pain killers they took for headaches.