Changes in volumetric hemodynamic parameters induced by fluid removal on hemodialysis in critically ill patients

Management of volume status is difficult in critically ill patients with renal failure. Volumetric hemodynamic indices are increasingly being used to guide fluid therapy in the intensive care unit (ICU), but are not established to monitor hemodialysis-induced fluid removal in critically ill patients. Using volumetric hemodynamic monitoring, changes in extravascular lung water index (EVLWI) and intrathoracic blood volume index (ITBVI) were measured immediately before and after hemodialysis sessions in 35 ICU patients. Additional hemodynamic and oxygenation related parameters were recorded at the same time, and online relative blood volume (RBV) monitoring was performed during hemodialysis. EVLWI decreased significantly with fluid removal (median 10.0 vs. 9.6 mL/kg, P = 0.001), whereas ITBVI remained stable (median 1012 vs. 1029 mL/m(2) , P = 0.402). Significant changes were also observed in stroke volume variation (median 12.0 vs. 13.0 %, P = 0.012), cardiac index (median 4.2 vs. 3.5 mL/min/m(2) , P = 0.003), mean arterial pressure (median 77 vs. 85.5 mmHg, P = 0.006), norepinephrine dose (median 0.092 vs. 0.114 μg/kg per min, P = 0.043), and hemoglobin values (median 9.5 vs. 10.4 gm/dL, P = 0.036). RBV decreased by 7.8% (median); there was no correlation with either the volumetric measurements or the other hemodynamic parameters recorded. EVLWI reduction with dialysis reflects the removal of excess body fluid, whereas preservation of cardiac preload is indicated by ITBVI stability. Volumetric hemodynamic measurements provide additional information concerning fluid status and are thus potentially useful to guide fluid removal on hemodialysis in critically ill patients.