Preoperative Goal-directed Fluid Therapy and Physiological Changes Following One-lung Ventilation

Intraoperative goal-directed fluid therapy (GDFT) is proposed to improve the outcomes of patients undergoing major surgery. In the GDFT algorithm, the employment of fluid bolus plays a crucial role. Dynamic fluid responsiveness parameters, such as stroke volume (SV) response and stroke volume variation (SVV), are precise fluid indicators that specifically determine patient volume status and are helpful for clinicians to determine the appropriate time for fluid bolus. During GDFT, fluid is commonly administered to maximize perfusion by maintaining patient blood volume at the plateau portion of the Frank-Starling curve by keeping patient at a lower SV response (i.e., SV increase < 10% and maintained for 20 minutes). However, maximization does not necessarily imply optimization; the role of fluid maximization of perfusion in GDFT remains controversial.Moreover, the importance of intraoperative GDFT in thoracic surgery has rarely been explored, because most intraoperative GDFTs have been conducted during abdominal surgery. Acute lung injury (ALI) following thoracic surgery remains a major source of morbidity and mortality after lung resection. Despite the advancement in both the surgical techniques and the perioperative management, the incidence of postoperative ALI remains remarkable. Risk factors are evident, including preoperative pulmonary function, type of surgical procedure, intraoperative fluid management, one-lung ventilation, and ventilator settings. Fluid management for thoracic surgery is challenging. Evidence has shown the association between excessive fluid administration and development of acute lung injury. Therefore, fluid restriction may benefit patients undergoing thoracic surgery. By contrast, restrictive fluid management incurs risks such as a hypovolemic state with impaired tissue perfusion which may result in organ dysfunction and in particular postoperative acute kidney injury. Accordingly, maintenance of perfusion through a maximized fluid protocol may be favorable. However, this debate has not yet been investigated.In this study, two fluid strategies guided by SV response, namely maximization and nonmaximization protocols, during intraoperative GDFT for patients undergoing thoracic surgery requiring one-lung ventilation. Clinical outcomes and perioperative changes in serum biomarkers of oxidative injury were compared between the two groups as the primary and secondary outcomes respectively.