This study is aim to assess the effect of goal-directed intraoperative fluid therapy on patient's postoperative incidence rates of complications, length of hospitalization and hospitalization cost.

This is an observational study followed cohort study design, due to the two therapies were not randomized assigned to the two cohorts. The details are described as follow.

The study will be conducted in patients undergoing either elective laparotomy of gynecological malignancies or elective major orthopaedic surgery under prone position in Peking Union Medical College Hospital. The study included two stages.

In the first stage, one cohort of 300 participants with conventional fluid therapy will be involved, in which 150 patients will be selected with laparotomy of gynecological malignancies and150 patients will be selected with orthopedic surgery. All the participants in this stage will follow conventional fluid therapy to direct the amount of intraoperative fluid. Specifically, the fluid will be administered based on the principle crystalloid solution (colloid solution =2-3:1). The total volume of fluid will be adjusted in accordance with blood pressure, heart rate and urine output of each patient. It is a standard procedure in Peking Union Medical College Hospital. Then, the incidence of postoperative complications of each group will be recorded. In addition, sample size will be estimated based on above study's results (estimated 100 participants).

In the second stage, goal-directed therapy will be applied to another cohort of 300 participants, in which 150 patients undergoing laparotomy of gynecological malignancies and 150 patients undergoing orthopedic surgery. Specifically, the fluid will be administered based upon real-time monitoring stroke volume variation and cardiac output achieved by the Flo-Trac monitoring system. The incidence of postoperative complications of each group will be recorded.

Inclusion Criteria:

1. Receiving elective laparotomy of gynecological malignancies (LGM): including cytoreductive surgery of ovarian cancer, radical hysterectomy and staging surgery of endometrial cancer ;
2. Major elective orthopedic surgery (OS): including spinal surgery, revision surgery of hip joints ;
3. Age ≥18 years, American Society of Anesthesiologists physical status I ～IV;
4. No arrhythmia;
5. Receiving general anesthesia;
6. Requiring monitoring of direct blood pressure due to the comorbidities of patients and the nature of surgical procedures.

Exclusion Criteria:

1. Emergent surgery;
2. Patients with aortic regurgitation;
3. Patients with aortic stenosis, peripheral arterial diseases or other diseases contradicting to arterial canalizations;
4. Patients with mental disorders or low intelligence quotient; patients who cannot cooperate or refuse to sign the consent.

Patients underwent either laparotomy of gynecological malignancies or orthopedic surgery