Fluid management in the perioperative setting: mind the kidney

Acute kidney injury (AKI) is one of the most frequent complications in critically ill patients and in the perioperative setting. The anatomical structure and the microvasculature of the kidney makes it highly vulnerable to hypoxia. Although fluid therapy is considered crucial in situations where improvement of cardiac output is needed, it can also contribute to AKI development when administered inappropriately. Hemodilution and anemia during cardio-pulmonary bypass have been demonstrated to be risk factors for AKI and they are likely to be a consequence of fluid administration. In order to assess the perfusion of the kidneys it is necessary to investigate the determinants of delivery of oxygen at the microcirculatory level. Indeed, fluids can decrease the capillary hematocrit and the functional capillary density, affecting the renal oxygenation and increasing the risk of AKI. Monitoring sublingual microcirculation can be a reliable tool to guide fluid administration, aiming to prevent or improve perioperative AKI.