الفهرس 
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Abstract
Fluid status assessment and management during operative period in cardiac surgery is considered as a clinical challenge especially in children. The key to anaesthesia in pediatric cardiac surgery is to maintain adequate CO beside the adequate myocardial oxygen supply and demand balance without hypo or hypervolemia
Since hypovolaemia is a common cause of perioperative circulatory failure in adults and children, Fluid administration is one of the maneuvers to augment cardiac output volume expansion is essential to improve the outcome in patient undergoing cardiac surgery. However unnecessary volume load may cause deterioration in myocardial function with the development of acute heart failure.
Also, The cornerstone of resuscitation of haemodynamically unstable critically ill, injured patients as well as those undergoing major surgery is often considered to be fluid loading. However, only roughly half of haemodynamically unstable patients respond to a fluid challenge, defined as an increase in stroke volume (SV) or cardiac output (CO) upon fluid loading. In other words.
Although rapid optimization of volume status has shown to improve outcome, extended fluid loading is associated with the development of pulmonary edema and increase the risk of acute respiratory distress syndrome (ARDS), resulting in increased morbidity and mortality. Little evidence is available for the type and exact dosing of fluid administration. Establishing volume status is complex, making accurate prediction of an increase in SV upon fluid loading, so-called fluid responsiveness.
Maintaining effective circulating blood volume and pressure are key components of assuring adequate organ perfusion while avoiding the risks associated with either organ hypo- or hyperperfusion especially during perioperative period.
\Hypotension is one of the most frequently encountered haemodynamic disturbances in the operative setting. In most patients, absolute or relative depletion of intravascular volume is the principal cause of arterial hypotension. However, impaired ventricular contractility, for example after cardiac surgery, may also cause arterial hypotension. (9)
In this situation, further volume loading is not accompanied by an increase in CO but may lead to deterioration of cardiopulmonary function. Therefore, it is important to identify patients in whom augmentation of cardiac preload leads to an increase in SV. Accordingly; it is of utmost importance to determine accurate parameters to guide fluid therapy and haemodynamic optimization, while avoiding administration of ineffective and possibly harmful therapy.(9, 10).
To avoid the potential deleterious effects of excessive fluid therapy, preload dependence assessment is crucial to guide fluid therapy to prevent unnecessary fluid overload. Thus, the identification of a reliable predictor of fluid responsiveness in the pediatric population is an essential step in the