Fluid therapy is the cornerstone of patient management in the perioperative setting. While a liberal approach to fluid therapy was used in the past to prevent hypovolemia and improve organ perfusion, it was shown that tissue inflammation and consequent extravascular leak led to fluid accumulation in the third space, contributing to perioperative complications. As evidence emerged that a positive fluid balance was associated with increased risk of adverse surgical outcomes as well as organ dysfunction, such as acute lung injury, acute kidney injury and prolonged duration of mechanical ventilation and ICU stay, restricted or goal-directed fluid therapy (zero-balance approach) began to replace the conventional approach to fluid management.

Whenever intravenous fluid therapy is administered for any reason, only a portion of the total fluid received stays inside the intravascular compartment; the rest extravasates into the capillary interstitial space. Adverse effects of intravenous fluid therapy often relate to this extravasation of intravascular fluid, as it causes tissue edema and decreased tissue oxygen delivery leading to poor clinical outcome. One of the four major Starling forces, the plasma colloid oncotic pressure determines the intravascular stay of fluid. Inflammation causes endothelial damage leading to leaky capillaries that exude fluid and protein, reducing the oncotic pressure. Albumin being a negative acute phase reactant is reduced in the perioperative setting and contributes to a lowered value of colloid oncotic pressure.

We postulate that this decreased plasma oncotic pressure might contribute to enhanced extravascular leak that leads to poorer outcomes. While a number of studies have shown adverse clinical outcomes associated with a positive fluid balance intra- and post-operatively, the effect of a reduced colloid oncotic pressure has not been studied in the perioperative period for non-cardiac surgeries.  Furthermore, no study has attempted to see if the ratio of positive cumulative fluid balance to colloid oncotic pressure can be a useful predictor for post-operative complications.

Study hypothesis: Higher cumulative fluid balance to estimated colloid oncotic pressure ratio will be associated with poorer outcomes in patients undergoing emergency abdominal surgery