Effects of Intraoperative Goal-Directed Fluid Therapy on the Incidence of Postoperative Complications Following Gastrointestinal Surgery

I. Background Excessive fluid loss is often reported in gastrointestinal surgical patients due to preoperative fasting and bowel preparations. Many factors may further exacerbate the lack of fluid volume, including intraoperative blood loss and fluid loss, anesthetic drug-induced peripheral vasodilatation, as well as systemic inflammatory response syndrome, systemic capillary leak syndrome, endothelial barrier dysfunction and transfer of intravascular fluid to the third space caused by surgical trauma.

Insufficient fluid infusion may cause hypovolemia and tissue hypoperfusion, which may delayed postoperative recovery and even induce postoperative acute renal failure. On the other hand, fluid overload can lead to edema, increased oxygen diffusion distance between lung mesenchyme and cells, then causing tissue ischemia, hypoxia, and acidosis and even affecting the recovery of gastrointestinal function and the healing of incision. It has been proved that improper fluid therapy in the perioperative period is associated with poor outcomes in patients with gastrointestinal surgery. Goal-directed fluid therapy (GDFT) regimen emphasizes the personalized fluid infusion to optimize the intraoperative hemodynamics and tissue perfusion, including rising stroke volume, increasing arterial oxygen saturation, which may result in improving postoperative outcomes.

Flo-Trac/Vigileo system is developed by Edwards Technology, and monitors the continuous cardiac output via peripheral arteries. The monitoring approaches of this system prove to be convenient, safe and minimally invasive. As an important indicator of the system, stroke volume variation (SVV) can accurately reflect the volume status of patients. The principle of SVV is the preload change, which is caused by the intrathoracic pressure changes between inspiratory and expiratory phases, will lead to arterial pulse pressure fluctuations, thus affecting stroke volume (SV). SV may vary under different volume loads. Through measuring and analyzing these differences and then assessing the circulation status, SVV provides guidance for fluid therapy. The continuous and real-time SVV monitoring can provide data of patients' circulation status, thereby optimizing clinical fluid treatment options and avoiding excessive or insufficient volume. For patients with gastrointestinal surgery, SVV guidance during the surgery can accurately regulate fluid infusion, which will contribute to the early postoperative recovery and improve patient prognosis.

In the present study, SVV-directed fluid therapy will be performed in patients with gastrointestinal surgery and then will be compared with conventional fluid treatment regimen in the mobility and mortality of postoperative complications, postoperative recovery, and length of hospital stay. The investigators are aiming to provide clinical evidences for reasonable intraoperative fluid management of such patients.

II. Objectives The aim of this study is to compare the effects of GDFT strategy with that of the conventional fluid management on the morbidity and mortality of postoperative complications, length of postoperative hospital stay, and medical expense, so as to provide clinical evidences for optimized intraoperative fluid management for patients undergone gastrointestinal surgery.