With the formula to achieve objectives, called Goal Directed Therapy (GDT), Rivers (2001) demonstrated how to reduce mortality in patients with severe sepsis and septic shock through the optimization of different haemodynamic variables for a dynamic and individualized view, instead of maintaining only an adequate Arterial Pressure (AP). Later publications support that the intraoperative GDT, used to maintain an adequate systemic oxygenation, can safeguard organs especially sensible from perioperative hypo-perfusion. High risk patients or even less pernicious patients to major surgery could profit from GDT by reducing incidence of postoperative complications, thus, improving and accelerating the outcome. The CO measurement in cardiology provides rewarding diagnostic and prognostic information for the management of patients with left- and right-sided cardiac dysfunction. Pulmonary Arterial Hypertension (PAH) may diminish the CO and promote right-sided heart failure, which untreated could be fatal. A simultaneous measurement of the preload also enables to assay the blood flow levels to discard states of hypovolemia or hypervolemia. For the fluid responsiveness evaluation, a small amount of solution can be previously administered as a tester, though this method is not recommended because it is irreversible. Another option is the passive leg raising test, which consists of inducing a fast and transient hemodynamic challenge without fluid infusion. By modifying the patient's position, a volume of venous blood from the lower body toward the right heart it is transferred, simulating an infusion of approximately 300ml. An increase in the CO (of = 10%) and AP within the next 60–90 seconds after leg elevation indicates a positive result, suggesting that the patient is fluid responsive and might benefit from additional fluid. By contrast if the test is negative, the patient should not be treated as it would be harmful. The fluid overload can raise extravascular water causing deleterious side effects in lungs. The basic mechanisms for the haemodynamic regulation are:  The explanation why the heart is capable of adapting to growing volumes of blood flow is called 'Frank-Starling's mechanism', which says that the more distended are the muscle during the filling, the more strength of contraction and quantity of blood pumped by the left-ventricle to the aorta. When the heart reaches a physiological limitation, then blood pumping cannot increase, although the venous return is further increased. The SVV contributes to know the state of volemia in ventilated patients and designates the point on the Frank-Starling curve where the patient is.