Non-invasive assessment of fluid volume status in theinterstitium after haemodialysis

Abstract

During dialysis excess fluid is removed from uraemic patients.The excess fluid is mainly located in the skin and subcutaneoustissues. In this study we wished, with two non-invasivetechniques, the IM (impression method) and BIA (bioimpedanceanalysis), to study what mechanical (IM) and electrical cellularmembrane (BIA) effects the fluid withdrawal has on thesetissues. The IM measures the resistive force of the tissues whenmechanically compressed. From the force curve two parametersare calculated, the F(0), indicative of interstitial tissuepressure and the FT corresponding to the translocation of tissuefluid (interstitial movable water).The BIA phase angle shift (ϕ), i.e. geometrical angulartransformation of the ratio between reactance and resistance,which has been associated with cellular membrane function, wasused as a measurement of electrical cellular membrane effects.Twenty patients were studied before and after haemodialysismeasuring the F(0), FT and ϕ. The results showed that thepatients lost a median of 3.7 kg during the haemodialysis. F(0)increased until after dialysis, but did not reach significantvalues, whereas FT increased significantly after dialysis,p < 0.001, as compared with before. After a peak at one hourpostdialysis the FT value returned to predialysis values at fourhours after termination of dialysis. Also ϕ increased frombefore to after dialysis, p < 0.001, but already after one hour itreturned to predialysis values.It is common knowledge that dialysis alters the dynamics of fluidin the interstitium of the skin and subcutis. We conclude that theimpression method is sensitive enough to detect and chroniclethese changes. Furthermore, with the BIA, (phase angle) signs ofchanges in the electrical properties of the tissues, possiblyreflecting cellular membrane function, could be detected.