Differential Secretion of Atrial and Brain Natriuretic Peptide in Critically Ill Patients

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones with natriuretic, vasorelaxant, and aldosterone-inhibiting properties. We analyzed the plasma of 178 critically ill patients for ANP, BNP, aldosterone, and serum sodium concentration, as well as serum and urine osmolality and sodium filtration fraction. Mean plasma concentrations of ANP and BNP were increased in critically ill patients compared with healthy controls (ANP, 14.3 ± 5.8 pmol/L versus 8.8 ± 3.2 pmol/L, P < 0.05; BNP, 26.2 ± 10.7 pmol/L versus 4.6 ± 2.8 pmol/L, P < 0.0001). The relative increases in ANP concentrations were comparable in all diseases. BNP concentrations, by contrast, showed a wider variation. The largest BNP concentrations were observed in patients who underwent cardiac surgical procedures and in patients with subarachnoid hemorrhage. ANP, but not BNP, was correlated with aldosterone levels (r = 0.4, P < 0.001), serum sodium (r = 0.42, P < 0.001), sodium filtration fraction (r = 0.3, P < 0.001), serum osmolality (r = 0.25, P < 0.01), urinary osmolality (r = −0.24, P < 0.01), and central venous pressure (r = 0.22, P < 0.01). ANP and BNP concentrations were increased in critically ill patients; however, this did not correlate with the severity of illness or mortality. Our data support a regulatory role for ANP in the maintenance of water and electrolyte balance. The physiologic role of BNP, by contrast, is less clear. ANP and BNP are not predictors for the severity of illness and mortality in critically ill patients.