[Extra cellular volume assessment methods in dialysis, a critical analysis]

The extra cellular volume is strictly proportional to the amount of sodium present in the body. Its clinical evaluation on dialysis (through clinical story, weight and blood pressure changes) often needs probing for dry weight by reducing progressively the post dialysis weight down to the point where hypotension regularly occurs. Common critics addressed to the clinical assessment of dry weight include lack of sensitivity, of objectivity and of repeatability. But non clinical methods are far from perfect. They are non invasive, but they are poorly sensitive and reproducible (except for bio impedance, but in very strictly equal operational conditions). Most of them (natriuretic peptides, inferior vena cava echography, on-line volemia) measure exclusively the plasma volume but not the extra cellular volume. Besides, they increase dialysis complexity and cost. None of them is so far validated for dialysis. The accurate and absolute value of extra cellular volume is useless in clinical daily practice. What is needed is a simple fast evaluation of the actual extra cellular volume relative to its ideal level (dry weight). The clinical method based on two very simple, costless objective measurements, weight and blood pressure, allows for fulfilling the goal, the continuous adjustment of extra cellular volume and blood pressure normalization.