REN and Hyponatremia: The predictors included pre- and peri-operative determinants as follows: patients demographics (age and sex), comorbidity of diabetes mellitus, usage of renin-angiotensin-aldosterone-system blockage, laboratory investigations (baseline eGFR, hyponatremia, anemia, hypoalbuminemia, and albuminuria), and surgical information (expected surgical duration and emergency surgery status).