Mean Systemic Filling Pressure and Heart Performance Predicting Fluid Responsiveness

The assessment of the cardiovascular state in critically ill patients is subject to difficulties in terms of the fact that several hemodynamic parameters, for example mean arterial blood pressure (MAP) and cardiac output (CO) supply insufficient information about the circulating volume and cardiac performance. There is a clinical need to adequate determination of intravascular volume status and therefore reliable predictors of fluid responsiveness are highly relevant. However, in determining the fluid status of a patient, the lack of appreciation of the venous side of the circulation persists today, which is greatly due to the inability to appropriately assess the venous side of the circulation. The importance of the venous part of the circulation is moreover reflected by the fact that an increase in venous resistance does reduce CO many times more than a similar increase in arterial resistance. Mean systemic filling pressure (Pms), which is defined as the pressure equal to the pressure which would be measured if the heart should suddenly stop pumping and all (arterial and venous) the pressures in the entire circulatory system should be brought to equilibrium instantaneously, is a good, complete and reliable reflection of the total intravascular fluid compartment. Passive leg raising (PLR) represents a "self-volume challenge" that predicts preload responsiveness and the transient hemodynamic changes on venous return can be directly monitored in ventilated patients, provided that there is an intact circulation, in order to test the amount of volume responsiveness.

Inclusion criteria

• Patients must be older than 18 years, and must be equipped with a pulse-contour cardiac output system with a central venous catheter. Patients will be subsequently connected to the hemodynamic monitoring device Navigator™. In those patients with clinical signs of inadequate tissue perfusion, passive leg raising and standardized fluid challenge will be performed.

Exclusion criteria

• Patients with assist devices (e.g. intra aortic balloon pump, Impella®, ECMO), patients with arrhythmias (either atrial of ventricular) will be excluded from the study. Also, patients with inguinal impairment or contraindications for a passive leg raising will be excluded (such as deep venous thrombosis or elastic compression stocking), head trauma, an increase intra-abdominal pressure suspected by clinical context and examination as well as patients with absolute contraindications for fluid challenge.