Background: The posthemodialysis plasma level of atrial natriuretic peptide (ANP) has been proposed as an index for an adequate fluid state in hemodialysis (HD) patients.
Patients and methods: We investigated the effect of fluid removal during HD on the interaction between intravascular volume and the vasoactive hormones ANP, vasopressin, adrenaline, noradrenaline, renin and aldosterone in 16 HD patients. Intravascular volume was examined with the 131I-labeled albumin method for blood volume (BV) and ultrasound for measurement of inferior vena cava diameter (IVCD).
Results: There was a significant decrease in BV, IVCD and ANP, but not in the other vasoactive hormones. Based on BV and IVCD measurements, the predialysis plasma ANP levels in the normovolemic and hypovolemic patients were significantly higher than in the hypervolemic patients. There was no significant difference between the postdialysis ANP levels in the hypervolemic and normovolemic patients and no significant correlations between ANP and BV and IVCD, respectively, but postdialysis ANP correlated significantly with the ultrafiltration rate (r = -0.51, p < 0.05), noradrenaline (r = 0.54, p < 0.05) and change in vasopressin (r = -0.50, p < 0.05). There were also correlations between ANP and age before HD (r = 0.50, p < 0.05) and after HD (r = 0.70, p < 0.0025).
Conclusion: We conclude that the usefulness of the plasma ANP level for assessment of the fluid state in HD patients is limited, since age and other factors than those directly related to volume influence the concentration of ANP.