A Comparison of Stroke Volume Variation for Prediction of Fluid Responsiveness

Inclusion Criteria: * Age 18≤ Age ≤65 * patients undergoinglaparoscopic elective surgery for gastrointestinal tumors under general anesthesia * 18 kg/m2≤BMI≤30 kg/m2 * ASA classification I-III * Patients signed informed consent form Exclusion Criteria: * Arrhythmias * The patient is diagnosed with severe cardiovascular disease（pulmonary arterial hypertension、left ventricular ejection fraction\< 50%、aortic aneurysm、extensive peripheral arterial occlusive disease,、significant valvulopathy） * Severe heart failure (METS\<4) * The patient is diagnosed with severe hepatic dysfunction (ChildePugh class C) * The patient is diagnosed with severe renal dysfunction (undergoing dialysis before surgery) * There is an infectious lesion on the skin or subcutaneous tissue where the non-invasive electrode piece is placed * History of allergy to anesthetic drugs * Weight\<40kg * Allergies to 6% hydroxyethyl starch, Fresenius Kabi, Deutschland