Fluid therapy in adults having non-cardiac surgery: A narrative review.

Background: Adequate intraoperative fluid therapy is essential, as both uncorrected fluid loss and excessive fluid administration are associated with increased complications. However, current practice varies widely. In this narrative review, we examine current concepts of intraoperative fluid therapy in adults having non-cardiac surgery, focusing on fluid type, volume of fluid, and fluid administration strategy. Results: Balanced crystalloids, compared to unbalanced crystalloids, more closely resemble the body's natural electrolyte composition. However, moderate intraoperative volumes of 0.9% saline do not seem to increase complications. Colloid fluids additionally contain larger molecules exerting colloid osmotic pressure and can be divided into synthetic and natural colloids. While concerns about synthetic colloids, especially hydroxyethyl starch, persist in intensive care medicine, intraoperative trials suggest that giving moderate volumes of hydroxyethyl starch is safe. The natural colloid human albumin theoretically offers a more favorable safety profile than synthetic colloids, but large randomized trials justifying the increased costs through improved outcomes are missing. Fluid administration strategies include calculation-based strategies, the concept of fluid responsiveness, and goal-directed fluid therapy. Calculation-based strategies rely on formulas to estimate fluid requirements. For patients having elective major non-cardiac surgery, a mildly positive intraoperative fluid balance (1-2 liters at the end of the procedure) is generally recommended. The concept of fluid responsiveness aims to assess the current hemodynamic status and evaluate whether a patient's cardiac output increases after fluid administration. However, even if fluid responsive, fluids should only be administered if there are additional clinical or metabolic signs of hypovolemia or tissue hypoperfusion. Goal-directed fluid therapy aims to optimize hemodynamics via treatment strategies by titrating fluids, vasoactive drugs, and inotropes to predefined hemodynamic target variables. Yet, goal-directed fluid therapy did not reduce complications compared to routine care in patients having non-cardiac surgery in recent multicenter trials. Conclusion: The optimal type of fluid for intraoperative fluid therapy remains uncertain and limited volumes of unbalanced crystalloids and hydroxyethyl starch appear to be safe in surgical patients. A mildly positive intraoperative fluid balance is generally recommended for patients having major non-cardiac surgery. Fluid responsiveness can help guide fluid administration, but should not be the only factor leading to fluid administration.