Probing the dry weight by bioimpedance: the resistance stabilization test

Probing dry weight (DW) was largely dependent on clinical subjective estimate until recently. New bedside non-invasive tools have been developed with the aim of providing more objective information on volume status and guiding physicians in the quest for DW. Among them, bioimpedance appears to be very promising in the achievement of this goal. We have developed a test aimed to assess DW in complicated hemodialysis (HD) patients and named it "RE.sistance S.tabilization T.est" (RE.S.T.). It is based on the following four items: 1. one or more HD sessions lasting 6 h with ultrafiltration (UF) rate ≤0.5 kg/h are planned; 2. bioimpedance measurements are determined injecting 800 μA at 50 kHz alternating sinusoidal current with a standard tetrapolar technique. Resistance (R) is recorded at the start of the treatment (R0) and every 15 min (Rt) during HD until the end of the 6-h session; 3. DW is defined as that achieved at the time point at which three consecutive R0/Rt ratios show in-between changes ±1% despite ongoing UF; 4. if at the end of the 6-h HD session R stabilization is not attained, a new 6-h HD treatment with UF rate ≤0.5 kg/h is planned until a bioimpedance DW (according to the item 3) is obtained. As said, we are applying RE.S.T. to assess DW in complicated HD patients. Here we report a paradigmatic case which illustrates quite brilliantly its clinical usefulness. The patient was admitted to our nephrology ward with a hypertensive crisis, a very large drug regimen notwithstanding. His DW was reduced by 5 kg after four 6-h HD sessions probing his DW by means of RE.S.T. He was discharged with a normal blood pressure and no need for anti-hypertensive drugs. In conclusion, RE.S.T. appears to be a (the) brilliant solution in solving the old problem of DW in HD patients.