Infusion treatment
All patients were randomly divided into 3 groups. In Group S1, patients received a continuous infusion of crystal solution (Ringer’s acetate solution) and colloid solution (hydroxyethyl starch 130/0.4 sodium chloride injection) through two devices connected to the peripheral vein. Vigileo was used to measure the SVV and control the fluid infusion rate to keep the SVV below 13%. The patients in Group S2 were monitored with the same parameters as those used in Group S1, the intraoperative COP of patients in Group S2 was monitored simultaneously, and the volume and proportion of the infusion of crystal and colloid liquid were adjusted by controlling the relative infusion speed of the two fluids so that the plasma colloid osmotic pressure of patients was maintained at 20 ~ 25 mmHg. We collected the upper serum of the blood sample after centrifugation and measured COP with a colloid osmotic pressure monitor (ONKOMETER BMT923). Patients in Group C received a conventional infusion regimen, and the total amount of input fluid = physiological requirements + preoperative cumulative loss + continued loss + third gap loss + compensatory volume expansion. Compensatory expansion capacity was supplemented with compound Ringer’s solution at 7 ml kg