The period of obstruction will have caused damage to the cells of the renal tubules and following relief of the obstruction there is likely to be a period of polyuria with the potential for renal leakage of various ions including Na+, K+, Ca2+, HCO3-, PO42-.
It is important to monitor these losses and replace accordingly.
The plan was to recheck U & Es in 4 hours and then readjust the composition of the iv fluids.