Utility of B-type natriuretic peptide and N-terminal pro B-type natriuretic peptide in evaluation of respiratory failure in critically ill patients.

STUDY OBJECTIVES: B-type natriuretic peptide (BNP) and N-terminal pro BNP (NTproBNP) have been shown to correlate with pulmonary arterial wedge pressure (PAWP) in patients with heart failure. We studied whether BNP and/or NTproBNP can differentiate high- vs low-PAWP respiratory failure in ICU patients. We also evaluated if BNP and NTproBNP will reflect accurately cardiac dysfunction and predict 30-day survival.

DESIGN: Prospective observational study of ICU patients in an urban teaching hospital.

PATIENTS: Forty-one consecutive patients with hypoxic respiratory failure undergoing pulmonary artery catheterization were enrolled between January and December, 2003.

INTERVENTIONS: BNP and NTproBNP were assayed from a venous blood sample. Hemodynamic variables were obtained at the time blood was drawn. Survival was documented at day 30.

MEASUREMENTS AND RESULTS: BNP and NTproBNP correlated significantly with each other (r = 0.656, p < 0.001) and inversely with hemodynamic markers of contractility: BNP with cardiac index (CI) [r = - 0.481, p < 0.02], and left ventricular stroke work index (LVSWI) [r = - 0.384, p < 0.02]; NTproBNP with CI (r = - 0.441, p < 0.02) and LVSWI (r = - 0.623, p < 0.001). BNP and NTproBNP did not correlate with PAWP. We created receiver operating characteristic (ROC) curves for detection of contractile dysfunction using different LVSWI cutoffs. Area under the ROC (AUROC) values were larger and more consistent for NTproBNP than for BNP. For LVSWI < 35 g.m/m(2): BNP AUROC = 0.643, NTproBNP AUROC = 0.885 (p < 0.02); for LVSWI < 30 g.m/m(2): BNP AUROC = 0.754 (p < 0.02) and NTproBNP AUROC = 0.884 (p < 0.001). Mean (+/- SE) concentrations did not differ between the survivors and non-survivors: BNP, 909.3 +/- 264.2 pg/mL vs 840.9 +/- 171.2 pg/mL; NTproBNP, 11,630.6 +/- 3,181.8 pg/mL vs 11,777.6 +/- 2,989.9 pg/mL, respectively.

CONCLUSIONS: NTproBNP and BNP failed to differentiate high- vs low-PAWP respiratory failure but were inversely correlated with indexes of cardiac contractility. With higher accuracy, NTproBNP may be a more discerning marker than BNP in patients with milder cardiac dysfunction. Neither peptide predicted short-term mortality.