B-type natriuretic peptide secretion without change in intra-cardiac pressure

Objective: In clinical cardiology, B-type natriuretic peptide (BNP) is used as a non-invasive surrogate marker for intra-cardiac filling pressures, particularly in patients with heart failure. It is unknown whether and to what extent increase in intravascular volume and/or sympathetic tone while maintaining constant intra-cardiac pressures leads to an increase in levels of BNP in vivo. Design and Methods: We aimed to test this hypothesis in an experimental in vivo model of patients directly after off-pump coronary artery bypass grafting admitted to the intensive care unit. These patients require high volumes of intravenous fluids titrated to keep intra-cardiac filling pressures and arterial blood pressure in the normal range while awakening from deep general anesthesia. In 27 consecutive patients, intra-cardiac filling pressures (using a pulmonary artery catheter) and levels of BNP were measured simultaneously every 6. h. Results: At 0, 6, 12, and 18. h, the pulmonary capillary wedge pressure remained constant (12. ±. 4, 13. ±. 3, 12. ±. 3, and 13. ±. 3. mmHg, respectively; p=. 0.351). Similarly, right heart filling pressures did not change during the study period. In contrast, BNP levels increased significantly during the study period: Median levels were 82 [IQR 37-162] pg/ml at 0. h, 153 [92-246] pg/ml at 6. h, 274 [156-392] pg/ml at 12. h, and 320 [200-528] pg/ml at 18. h (. p<. 0.001). No significant correlation between BNP levels and pulmonary capillary wedge pressures was found (. r=. 0.052; p=. 0.604). Conclusions: After cardiac surgery, BNP cannot be considered a reliable non-invasive surrogate for PCWP. In vivo, substantial BNP secretion occurs independently of PCWP in a setting of increasing intravascular volume and consciousness/sympathetic tone.