Different Methods for Assessment of Fluid Responsiveness in Hypovolemic Patients

Abstract

Hypovolemia is a decrease of the volume of circulating blood, it may be due to external fluid losses caused by bleeding or losses from the gastrointestinal or urinary tracts, skin surface, or internal losses due to extravasation of blood or exudation or transudation of body fluids. Relative hypovolemia follows increases in venous capacitance due to release of inflammatory mediators as in sepsis or as a side effect of drugs. In these distributive forms of circulatory failure, the intravascular volume may be normal, but the increases in the capacity of the vascular bed preclude adequate venous return. Shock is best defined as a life-threatening, generalized form of acute circulatory failure associated with inadequate oxygen utilization by the cells. It is a state in which the circulation is unable to deliver sufficient oxygen to meet the demands of the tissues, resulting in cellular dysfunction. The diagnosis of acute circulatory failure is based on a combination of clinical, hemodynamic and biochemical signs. The clinical signs of shock typically include arterial hypotension (although this is not always present), associated with signs of altered tissue perfusion, the three organs readily accessible to clinical assessment of tissue perfusion are the: Skin (degree of cutaneous perfusion); Kidneys (urine output) and Brain (mental status). Fluid responsiveness is a measure of ‘preload dependence’ or ‘preload reserve’ but not all ‘fluid responders’ necessarily need volume loading. The initial assessment of volume status is most often based on clinical signs and symptoms in the prediction of fluid responsiveness, like skin turgor, urine color or production, fluid balance and the presence of peripheral edema. A comprehensive assessment for the underlying etiology of shock should be performed after stabilization. Laboratory tests should be performed early in the evaluation of patients with undifferentiated hypotension/shock to identify the cause of shock and/or early organ failure. The clinical detection of tissue hypoperfusion implies the need to adopt measures to improve oxygen transport. In this hemodynamic resuscitation process, the first step always includes the need to optimize volemia. Consequently, and in addition to the above mentioned goals of the resuscitation process, it is advisable from the start to monitor some parameter estimating preload dependency and which can be of help in making initial resuscitation