[Effect of automated blood volume control on the incidence of intra-dialysis hypotension].

INTRODUCTION: Hypotension is the major cause of morbidity during hemodialysis (HD), occurring in about 20% of HD patients. Hypovolemia generated from blood volume (BV) contraction dependent on the ultrafiltration rate (UFR) and on the plasma refilling rate, is a major factor in the pathogenesis of intradialytic hypotension (IDH). Hemocontrol biofeedback system (Hemocontrol, Hospal, HBS), incorporated in the bicarbonate HD, modulates BV contraction rate by adjusting the UFR and dialysate conductivity (DC) in order to obtain predetermined BV trajectories. In the present study, HBS treatment was compared with carbonate HD to assess the efficacy in lowering the hypovolemia-associated morbidity.

PATIENTS AND METHODS: The study included 7 hypotension-prone uremic patients, mean age 69.5 +/- 6.8 years, on maintenance HD for 44 +/- 30.0 months, with over 20% IDH during 1-month observation. Treatment periods of 1 month bicarbonate HD (UFR profiles, constant DC) were compared with a follow-up period of 1-month HBS treatment (monitoring of BV and automatic adjustment of UFR and DC). The number of IDH, changes in BV, UFR, and the values of systolic and diastolic blood pressure (BP) during HD and HBS were analyzed.

RESULTS: The incidence of symptomatic hypotension was considerably lower in HBS (11%, 1.3 IDH/patient) than in HD (39%, 4.6 IDH/patient), p < 0.005. Therapeutic interventions with 0.9% NaCl infusion were used in 28 IDH during HD and 8 IDH during HBS. In patients with the incidence of IDH 30% and < 30% during HD, the number of hypotension episodes was reduced during HBS by 33.3% and 20.9%, respectively. There was no statistically significant difference between BV monitored during HBS and HBS at 120, 180 and 240 min, except for t 60 min (HD = 5.99%, HBS = 6.68%, p < 0.027). No statistically significant difference was observed (t-test) either in pre-HD and post-HD BP between the runs, or in UFR.

DISCUSSION: The study showed it to be possible, by means of a technique for constant and automated BV control, to reduce the IDH incidence by affecting vascular refilling. Using BV automated regulation according to a pre-established curve, the system adjusts single oscillations of plasma refilling, affecting two output variables: UFR and sodium concentration in the dialysate which determines DC. In this study we found no statistically significant differences in final BV values during the two treatments. The lower incidence of IDH during HBS could be the consequence of not only smaller BV decrease but also of a greater stability of BV during HD and of protection from abrupt BV decrease. In both treatments, BV were considerably different only for t 60 min (HBS > HD), possibly due to the characteristic UFR profiles in HBS, with initially intense UFR. DC variations could be another important reason for higher cardiovascular stability. The increased concentration of sodium in dialysate enhances vascular refilling by affecting plasma osmolarity and by stimulating watershift from intracellular into extracellular space. Interdialytic body weight gain and BP did not differ between the two treatments, possibly due to unchanged sodium balance in both treatments.

CONCLUSION: Compared to HD, HBS is effective in lowering IDH incidence. Intradialytic measurement and modeling of BV to trajectories is a useful method for lowering hypovolemia-associated morbidity in patients with dialysis cardiovascular instability.