Perioperative fluid management remains controversial. Until recently, fluid management was guided by targets such as urine output, static pressures, blood pressure, and other physiologic variables. Such physiologic signs, however, are inadequate for detecting subclinical hypovolemia. This has prompted the emergence of an approach to fluid administration based on stroke volume and cardiac output—a “flow-guided” approach—designed to overcome the inadequacies of conventional physiologic signs and improve outcomes. Recent technological advances are permitting noninvasive guidance of intravenous fluid therapy to optimize intravascular volume status.
This article reviews the rationale for perioperative fluid management, strategies for perioperative fluid therapy and their associated outcomes, the types of volume expanders used, and considerations for improving perioperative fluid administration.
WHY FLUID MANAGEMENT MATTERS
Postoperative complications predict survival
In 2005, Khuri et al published a study of survival after major surgery that starkly illustrated the prognostic importance of postoperative complications. 1 In an effort to identify predictors of long-term survival, they analyzed a National Surgical Quality Improvement Program database of 105,951 patients who underwent eight common operations at Veterans Administration facilities. They found that the most important determinant of reduced postoperative survival over 8 years of follow-up was the occurrence of a complication within 30 days after surgery. The presence of a postoperative complication was a stronger predictor of death than any intraoperative or preoperative risk factor.
Fluid management is key to preventing complications
Optimizing perioperative fluid management is essential to reducing the risk of postoperative complications and mortality. Surgical patients are more likely to have serious complications and die if they have limited physiologic reserve. Adequate fluid administration may reduce the stress response to surgical trauma and support recovery.
Building on early work showing that survivors of major surgery have consistently higher postoperative cardiac output and oxygen delivery (DO 2) than do nonsurvivors, 2,3 a seminal study by Shoemaker et al showed that these types of blood flow–related parameters are predictive of both survival and complication-free survival. 4 Specifically, Shoemaker and his team showed that a protocol designed to achieve DO 2 of at least 600 mL/min/m 2 was associated with reductions in both postoperative complications and death. 4
PROBLEMS WITH PERIOPERATIVE FLUID THERAPY―AND EFFORTS TO OVERCOME THEM
Despite the utility of fluid management in reducing postoperative complications, perioperative fluid therapy is fraught with several fundamental problems:
- Blood volume cannot be evaluated accurately.
- Fluid overload cannot be identified accurately, apart from tissue edema as a result of gross fluid overload.
- Hypovolemia cannot be identified accurately. Commonly measured variables (heart rate, blood pressure, base excess, lactate) are late markers, and the patient’s status upon admission to the operating room is often unknown.
- Tissue perfusion cannot be evaluated accurately. Although lactate and venous oxygen saturation are surrogate markers, genuinely accurate markers for tissue perfusion are lacking.
For these reasons, fluids are commonly administered without the guidance of direct markers of fluid status.
Assessing flow-guided fluid therapy
These shortcomings prompted me and several other researchers to assess the evidence regarding a flow-guided approach to fluid administration, which aims to achieve maximal cardiac output and stroke volume while avoiding excess fluid administration. We conducted a systematic literature search for randomized controlled trials evaluating the postsurgical effects of perioperative fluid therapy to increase global blood flow to explicitly defined goals, after which we performed a meta-analysis of the 22 qualifying studies. 5 The trials collectively included 4,546 patients undergoing relatively high-risk elective or emergency surgery, consisting of general, vascular, cardiac, orthopedic, and urologic procedures. Overall mortality in these trials was 10.6% (481 deaths). The primary outcome assessed was mortality; secondary outcomes included morbidity and length of stay in the hospital and in the intensive care unit. Outcomes were assessed according to the timing of the intervention, the fluid type, and explicit measured goals. Fluids were given to all patients, usually as a dynamic bolus, using a flow-guided approach above and beyond that of the control group.