Although individualized or goal-directed approach has been advocated, a reliable index is still required to help monitor the volume status timely and efficiently. Dynamic indexes, such as pulse pressure variation (PPV) and stroke volume variation (SVV), have been shown to be clearly superior to more commonly measured static preload variables, such as pulmonary artery occlusion pressure (PAOP) and central venous pressure (CVP). The reliability of dynamic indexes in monitoring the volume status and predicting fluid responsiveness have been validated. Fluid optimization guided by SVV and PPV is beneficial to hemodynamic stability and can decrease mortality and reduce postoperative complications. However, the usefulness of dynamic indexes in elderly patients has not been previously investigated. This study aimed to evaluate whether dynamic indexes PPV and SVV can reliably predict fluid responsiveness in elderly patients, and to determine their thresholds in elderly patients.

Inclusion Criteria:

• 1.Patients undergoing gastrointestinal surgery 2.Age between 18 and 80 3.ASA I ~II. 4.BMI 18 ~ 24 kg/m2

Exclusion Criteria:

• 1.arrhythmias 2.intracardiac shunts 3.severe hypertension (SBP ≥ 160 mmHg or DBP ≥ 100 mmHg) 4.pulmonary hypertension 5.chronic obstructive pulmonary disease 6.peripheral vascular obstructive disease 7.receiving long-term treatment with vasopressors.