Abstract
Achievement of a normal hydration status is one of the major targets of hemodialysis. It is based on the estimation of "dry weight", the term used to define normal body fluid content. The concept of dry weight in hemodialysis patients is clinically undisputed, but it is not always easy to achieve in this population. Assessment of hydration status by clinical evaluation is imprecise and often unreliable. Measurement of the inferior vena cava (IVC) diameter has been shown to reflect individual fluid status. The relationship between variation in IVC diameter before and after hemodialysis session and weight loss has been investigated. Ultrasound (US) measurement of the IVC diameter is considered a valid measure of the hydration status and is routinely used in hemodialysis patients. Moreover, a relationship between IVC diameter, respiratory activity and hydration status, evaluated by considering both plasma volume and central venous pressure, has been demonstrated. In conclusion, assessment of hydration status based on blood pressure and central venous pressure can be considered reliable only in patients without signs of heart failure.