Through preoperative fluid therapy, to investigate whether it can alleviate the microcirculation dysfunction after induction of anesthesia, and reduce the incidence of perioperative fluid therapy-related complications, thereby accelerating rehabilitation.

Patients undergoing minimally invasive coronary artery bypass graft surgery were randomly divided into crystal group, colloid group and control group. The preoperative fluid reactivity was evaluated according to the passive leg lifting test (PLR). When stroke volume increased (△SV)>16%, the patients in the crystal (carbonate Ringer solution) and the colloid group (hydroxyethyl starch solution) were treated with volume therapy, while the control group was not treated with PLR test and volume therapy. Vascular occlusion test was used to observe the effect of anesthesia induction on tissue oxygen saturation recovery slope (RecStO2) after volume therapy, Goal-directed fluid therapy was used during operation, and the postoperative microcirculation function and the incidence of related complications were observed.

Inclusion Criteria:

• Age ≥ 18 years old
• Plan to undergo elective minimally invasive coronary artery bypass grafting (left anterior descending branch);
• Sign informed consent

Exclusion Criteria:

• Left ventricular ejection fraction <40%
• Diabetes
• Renal insufficiency (serum creatinine>177umol/L)
• Liver insufficiency (AST, ALT>3 times)
• Peripheral vascular disease
• Carotid artery stenosis (>60%) VOT test contraindications (arm deformity, burns, arteriovenous shunt)
• Use glucocorticoids, vasoactive drugs, inotropic drugs or intra-aortic balloon counterpulsation (IABP)
• Allergic to colloidal fluids