Intraoperative fluid therapy (IFT) is an integral part of anesthesia care during surgery. Its main indication is the optimization of oxygen supply to the tissues. For elective surgery that is not associated with higher blood loss and a long period of preoperative fasting, including fluids IFT is dosed to cover the basal daily need for fluids. However, it is not clear whether this fluid dose is optimal. Surgery is a stress factor that leads, among other things, to damage of the endothelial glycocalyx (EG). EG binds a significant amount of plasma, which is released during EG destruction and causes relative hemodilution.

Isovolumic hemodilution is an established intraoperative procedure that serves to better control bleeding in procedures where bleeding is expected. However, partial hemodilution occurs even with standard IFT, and even when fluids are hardly given at all. Flow parameters in microcirculation have not yet been described depending on IFT conduction. The parameters of the microcirculation reflect its functioning, which will consequently affect the postoperative phase of the patient's moaning and clinical outcome.

Intraoperative fluid therapy (IFT) is an integral part of anesthesia care during surgery. Its main indication is the optimization of oxygen supply to the tissues. IFT is tailored to the surgical performance, blood loss, and patient (comorbidities, length of preoperative fasting, hydration level, volemia status). For elective surgery that is not associated with higher blood loss (< 200 ml) and a long period of preoperative fasting, including fluids (fluids per os < 2 hours before the procedure), IFT is dosed to cover the basal daily need for fluids (approx. 1-2 ml) /kg.hour-1). However, it is not clear whether this fluid intake is optimal. Surgery is a stress factor that leads, among other things, to damage of the endothelial glycocalyx (EG), which is a thin carbohydrate layer on the endoluminal side of endothelial cells, which is of fundamental importance for the physiology of microcirculation and tissue metabolism. EG also binds a significant amount of plasma (estimated up to 1.7 liters), which is released during EG destruction and causes relative hemodilution.

Isovolumic hemodilution is an established intraoperative procedure that serves to better control bleeding in procedures where bleeding is expected (e.g. cardiac surgery using an extracorporeal circuit or vascular surgery). However, partial hemodilution occurs even with standard IFT, and even when fluids are hardly given at all. Flow parameters in microcirculation have not yet been described depending on IFT conduction. The parameters of the microcirculation reflect its functioning, which will consequently affect the postoperative phase of the patient's moaning and clinical outcome.

Inclusion Criteria:

• elective recumbent and laparoscopic surgery
• informed consent

Exclusion Criteria:

• blood loss over 250 ml
• hemodynamic instability requiring noradrenaline infusion