After approval from the ethics and research committee of Faculty of Medicine, Cairo University, an informed consent will be obtained from each patient's next of kin. Arteial cathter will be inserted in radial artery and connected through an arterial line to invasive arterial blood pressure monitor. Electrical Cardiometry will be attached to patient through the placement of four skin sensors on the neck and left side of the thorax12. A set of hemodynamic measurements will be obtained at baseline and after infusing a fluid challenge (FC) of 150-250 ml normal saline over 5-10 minutes.Fluid-responders are patients with a SV increase ≥10% after fluid challenge (FC).