Detection limit of methods to assess fluid status changes in dialysis patients

Technical systems for an accurate and practicable fluid management of dialysis patients are urgently needed, since current clinical methods are partially subjective, imprecise, and time consuming. Such new systems should not only allow the determination of the target normohydration weight, but also must be able to detect clinically relevant changes in fluid volume (similar to 1 l). This study focuses on the systematic analysis of the detection limit of several candidate methods for fluid management. In a cohort of 16 new dialysis patients, several candidate methods were applied in parallel during each treatment of the initial weight reduction phase: the measurement of vena cava diameter (VCD), vena cava collapsibility index (CI), the blood volume drop during an ultrafiltration (UF) bolus (Delta relative blood volume (RBV) -), the rebound after the UF bolus (Delta RBV+), and the extracellular fluid volume determined with whole body bioimpedance spectroscopy (BIS). A clinical reference method was used to manage the fluid status of patients. All methods showed significant correlations with predialysis weight. The detection limits W-lim of candidate methods for changes in fluid status were assessed as W-lim = 0.87 kg +/- 0.64 kg (BIS), 1.74 kg +/- 1.56 kg (VCD), 2.3 kg +/- 1.0 kg (Delta RBV-), 7.4 kg +/- 8.5 kg (CI), 40 kg7108 kg (Delta RBV+). Only BIS shows a satisfactorily low detection limit Wlim, whereas Wlim was rated as critical for the VCD and Delta RBV- methods, and as unacceptable for the CI and Delta RBV_ methods. Bioimpedance spectroscopy appears to be the most promising method for a practical fluid management system in dialysis.