Haemodynamics and electrolyte balance: a comparison between on-line pre-dilution haemofiltration and haemodialysis.

BACKGROUND: An important advantage of convective therapies is improved vascular reactivity. However, it is not well known whether the vascular response during convective therapies remains superior when compared to haemodialysis (HD) with an adjusted temperature of the dialysate. It has also been suggested that convective therapies may impair small electrolyte removal through an effect on the Donnan equilibrium. In the present study, we compared the haemodynamic response and small electrolyte removal between pre-dilution on-line haemofiltration (HF) and HD procedures. METHODS: Cardiac output (CO), central blood volume (CBV) and peripheral vascular resistance (PVR) were assessed, using the saline dilution technique, in 12 stable patients during HF and HD with two different temperatures of the dialysate [36.5 and 35.5 degrees C (HD(36.5) and HD(35.5))]. Balances for sodium, potassium, calcium and conductivity were assessed using total dialysate/filtrate collections. Target filtration volume for HF was 1.2 times body weight. The temperature of the infusate was 36.5 degrees C. RESULTS: The change (Delta) in CBV was less during HD with a dialysate temperature of 35.5 degrees C (-0.03+/-0.14 l; P<0.05) compared to HF (-0.16+/-0.05 l) and HD(36.5) (-0.11+/-0.14 l), but the other haemodynamic parameters did not differ between the studied techniques. DeltaPVR was significantly related to DeltaCBV (r = -0.46; P<0.01), whereas DeltaCBV was related to ultrafiltration rate (r = -0.34; P = 0.05). DeltaCO was related to DeltaCBV (r = 0.62; P<0.001). Solute balances did not differ between HF and HD. CONCLUSION: Using the saline dilution method, no difference in the change in CO and PVR was observed between on-line HF vs HD(36.5) and HD(35.5). Only CBV declined to a significantly lesser degree during HD(35.5), although absolute differences were small. Changes in the other haemodynamic variables appeared more dependent upon the degree and rapidity of fluid removal than upon the treatment modality. No difference in small electrolyte balance was observed between HF and HD, suggesting that ionic removal is not impaired during on-line HF.