Effect of pre- and peri-operative hypovolemia on postoperative outcomes in patients undergoing elective colorectal cancer surgery

Interventions: Preoperation dehydration and postoperation dehydration group:Urine and blood before and after operation room are collected separately;Preoperation dehydration and postoperation normal group:Urine and blood before and after operation room are collected separately;Preoperation normal and postoperation dehydration group:Urine and blood before and after operation room are collected separately;Preoperation normal and postoperation normal group:Urine and blood before and after operation room are collected separately Primary outcome(s): Urine color;Urine specific gravity;Urine osmotic pressure;Urinary creatinine concentration;Postoperative complications and mortality Study Design: Case series