B-type natriuretic peptide (BNP) and N-terminal-proBNP for heart failure diagnosis in shock or acute respiratory distress.

Background: Plasma B-type natriuretic peptide (BNP) assay is recommended as a diagnostic tool in emergency-room patients with acute dyspnea. In the intensive care unit (ICU), the utility of this peptide remains a matter of debate. The objectives of this study were to determine whether cut-off values for BNP and N-terminal-proBNP (NT-proBNP) reliably diagnosed right and/or left ventricular failure in patients with shock or acute respiratory distress, and whether non-cardiac factors led to an increase in these markers.

Methods: Plasma BNP and NT-proBNP levels and echocardiographic parameters of cardiac dysfunction were determined in 41 patients within 24 h of the onset of shock or acute respiratory distress.

Results: BNP and NT-proBNP levels were higher in the 25 patients with heart failure than in the other 16 patients: 491.7 +/- 418 pg/ml vs. 144.3 +/- 128 pg/ml and 2874.4 +/- 2929 pg/ml vs. 762.7 +/- 1128 pg/ml, respectively (P < 0.05). In the diagnosis of cardiac dysfunction, BNP > 221 pg/ml and NT-proBNP > 443 pg/ml had 68% and 84% sensitivity, respectively, and 88% and 75% specificity, respectively, but there was a substantial overlap of BNP and NT-proBNP values between patients with and without heart failure. BNP and NT-proBNP were elevated, but not significantly, in patients with isolated right ventricular dysfunction. Patients with renal dysfunction and normal heart function had significantly higher levels of BNP (258.6 +/- 144 pg/ml vs. 92.4 +/- 84 pg/ml) and NT-proBNP (2049 +/- 1320 pg/ml vs. 118 +/- 104 pg/ml) than patients without renal dysfunction.

Conclusion: Both BNP and NT-proBNP can help in the diagnosis of cardiac dysfunction in ICU patients, but cannot replace echocardiography. An elevated BNP or NT-proBNP level merely indicates the presence of a 'cardiorenal distress' and should prompt further investigation.