Hypotension is associated with postoperative complications. Preoperative fluid infusion can effectively prevent post-induction hypotension of general anesthesia. Previous studies only focused on the hemodynamics after preoperative fluid infusion. Pre-operative fluid infusion can reduce the incidence of post-operative complications by preventing post-induction hypotension. The patients who is 18 years or older and undergo elective non-cardiac surgery with general anesthsia will be enrolled. The intervention is intravenous infusion of colloids or crytalloids before induction of general anesthesia. The primary outcome is the incidence of post-operative complications within 30 days.

Post-induction hypotension occurs in 30-40% of patients undergoing surgery under general anesthesia. Perioperative hypotension is a significant independent risk factor for post-operative myocardial injury, acute kidney injury, stroke, and significantly increases 30-day mortality rate after surgery. Perioperative hypotension has been attributed to absolute or relative hypovolaemia secondary to pre-operative fasting and to the vasodilatory and negative inotropic effects of certain induction agents. Low baseline blood volume is a risk factor for post-induction hypotension. The general consensus remains that patients entering the operating room require fluids to make up for reduced pre-operative intake. Intravenous administration of 500 mL of crystalloid solution before induction of anaesthesia did not decrease the overall incidence of cardiovascular collapse during tracheal intubation of critically ill adults compared with no fluid bolus. Among patients in the intensive care unit requiring fluid challenges, intravenous crystalloid boluses of 250 ml before intubation did not reduce 90-day mortality. Preloading colloids reduced the occurrence of post-induction hypotension and vasopressor use, improved CI, and reduced SVV during the early intraoperative period. It is unknown whether pre-operative colloids infusion can reduce the incidence of post-operative complications by preventing post-induction hypotension. We will enroll patients with 18 years or older and undergoing elective surgery under general anesthsia. The participants in colloid group will receive intravenous colloids 5ml/kg before induction of anesthesia; who in crystalloid group will receive intravenous Ringer's solution 5ml/kg before induction of anesthesia. The primary outcome in this study is the incidence of post-operative complications (Clavien-Dindo) within 30 days. The secondary outcomes include the incidence of post-induction hypotension, the doses of vasopressors and inotropes intra-operatively, lengths of stay in hospital (LOS) post-operatively, optimal recovery post-operatively within 5 days.

Inclusion Criteria:

• 18 years or older
• ASA I-III
• Undergoing elective non-cardiac surgery under general aneathesia

Exclusion Criteria:

• Allergic to colloids
• Severe heart diseases ( Ejection Fraction lower than 35%)
• Presence of renal failure pre-operatively (defined as eGFR < 30 mL/min/1.73 m2 and/or patient receiving renal replacement therapy)
• Morbid obesity (BMI > 37.5kg/m2 or > 32.5kg/m2 with metabolic diseases)
• Presence of a coagulopathy at screening (defined as platelet count < 100 × 109/L and/or a prothrombin time < 70% and/or an activated partial thromboplastin time (aPTT) >35 s and/or fibrinogen <1 g/ L)
• Presence of liver injury (defined as Child-Pugh C)
• Pre-operative electrolyte disturbances with Na >160 mmol/L or <120 mmol/L
• Patients with preoperative intracranial hypertension requiring dehydration treatment