The issue of fluid balance and mortality

Appropriate use of fluid infusion in cardiac surgery patients is of primary importance in the perioperative period in order to optimize cardiac output and oxygen delivery and to reduce the use of vaspressors and inotropes. Fluid infusion is usually triggered by arterial hypotension, low urine output and signs of inadequate tissue oxygenation (e.g. hyperlactatemia). This general rule, however, may not be applied when the heart is working in the flat part of the Frank Starling curve, where hypervolemia may cause excessive increase of filling pressures and tissue edema. In this light, it is mandatory to carefully dose the exact amount of fluids to administer in order to avoid the risk of volume overload. In this issue of HSR Proceedings in Intensive Care and Cardiovascular Anesthesia, Arora and co-workers shed some light on the issue of perioperative fluid administration to cardiac surgery patients and its correlation to mortality (1). The authors clearly showed how the effects of intravascular filling correlates with mortality, especially if the amount of given fluids exceeded four litres in the perioperative period. This effect remained significant even after adjustment for the presence of acute kidney injury and/or hypotensive events. The authors did not specify if the nature of infused fluids had a role on patients outcomes nor if specific treatments such as early/aggressive perioperative ultrafiltration might inversely correlate with mortality. More than five years ago, data coming from the Prospective Pediatric Continuous Renal Replacement Therapy registry showed that survival rates in patients with multiorgan dysfunction syndrome were significantly better for patients with less than 20% fluid overload (58% vs 40% survival rate) at continuous renal replacement therapy initiation (2). Fluid balance is probably underestimated in critically ill adults where a huge fluid volume amount is infused in order to target hypovolemia and organ perfusion. Few clinical invesIn vi te d ed it or ia l The issue of fluid balance and mortality