Body Fluid Spaces and Blood Pressure in Hemodialysis Patients During Amelioration of Anemia With Erythropoietin

Blood pressure (BP) may increase in hemodialysis patients during treatment of anemia with recombinant human erythropoietin (r-HuEPO). Since fluid volume is a determinant of BP in dialysis patients, changes in body fluid spaces during r-HuEPO therapy could affect BP. Thus, ⁵¹Cr-labeled red blood cell (RBC) volume, inulin extracellular fluid (ECF) volume, and urea total body water (TBW), as well as cardiac output, plasma renin activity (PRA), and plasma aldosterone concentration were determined postdialysis before and after r-HuEPO therapy in patients in whom changes in BP could be managed by ultrafiltration alone. Eleven patients entered the study: one had a renal transplant and two required addition of anti hypertensive drug therapy and were excluded; eight, of whom two required anti hypertensive drug therapy following the study, were included in the analyses. Results revealed an increase in predialysis hemoglobin from 67 to 113 g/L (6.7 to 11.3 g/dL) (P = 0.001) during 18 ± 6 weeks of therapy. Predialysis diastolic BP increased from 80 to 85 mm Hg (P = 0.07), while postdialysis diastolic BP was unchanged at 73 mm Hg. ⁵¹Cr-RBC volume increased, from 0.7 to 1.3 L (P = 0.004). ECF tended to decrease, from 13.7 to 10.8 L (P = 0.064), while TBW decreased to a similar extent, but not significantly, 34.3 to 31.2 L (P = 0.16). Postdialysis ECF volume was positively correlated with mean arterial BP at baseline (r = 0.89, P = 0.007) and after therapy (r = 0.74, P = 0.035). However, the regression lines for this relationship were different (P = 0.022) before and after therapy. Cardiac output, PRA, and plasma aldosterone concentration results were variable, but did not change. While conclusions are limited by the small number of patients, ECF volume tended to decrease and appeared to be an important determinant of BP both before and during amelioration of anemia in a subset of patients not requiring an increase in anti hypertensive drug therapy. However, the findings that postdialysis BP was unchanged despite a decrease in ECF, as well as the difference in regression lines between BP and ECF before and after therapy, suggest the relationship between ECF volume and BP was reset during r-HuEPO therapy. Although the mechanism is not clear, in certain patients the effect could be a loss of BP control by volume removal alone and increased need for anti hypertensive drug therapy during amelioration of anemia.