Dry weight in hemodialysis: volemic control

In dialysis patients the chronic fluid overload may represent a nonphysiologic condition which brings both arterial hypertension and hemodynamic instability. Volume expansion is significantly correlated to casual predialysis blood pressure and 24-hour arterial pressure. The normalization of the patient hydration status is not only followed by a reduction in pressure values but also by an improvement of the circadian blood pressure rhythm. On the other hand, hypovolemia and underhydration combined with an impaired cardiovascular regulatory response may generate the dialysis-related hypotension. Many techniques have been introduced to obtain an objective measurement of the hydration status: postdialysis radiological chest examination, plasma atrial natriuretic peptide (ANP), and plasma cyclic guanidine monophosphate (cGMP) levels, multifrequency electrical bioimpedance and the continuous plasma volume measurement. The latter, alone or in combination with provocative tests (stop and go of the ultrafiltration), may help in optimizing plasma volume contraction. The plasma volume monitoring avoids the risk of hypovolemic hypotension and facilitates the achievement of a correct dry body weight. The biofeedback system, exploiting the automatic control of the intradialytic variations, may represent an additional advantage in the formulation of an ideal postdialysis blood volume that overlaps the patient's dry weight.