Hyper osmolality does not modulate natriuretic peptide concentration in patients after coronary artery surgery.
BACKGROUND
The heart secretes natriuretic peptides (NPs) in response to myocardial stretch. Measuring NP concentrations is a helpful tool in guiding treatment. It has been suggested that sodium ion and hyperosmolality could affect NP excretion. If this is true, peri-operative NP measurements could be inconsistent when hypertonic solutions are used. With different osmolalities but equal volumes of hydroxyethyl starch (HES)--and hypertonic saline (HS)--infusions, this double-blinded study tested the hypothesis that osmolality modulates the excretion of NPs.


METHODS
Fifty coronary surgery patients were randomized to receive within 30 min 4 ml/kg either HS or HES post-operatively. Samples for analysis of atrial NP (ANP), brain NP (BNP), plasma and urine sodium and osmolality and urine oxygen tension were obtained before and 60 min after starting the infusions and on the first post-operative morning. The haemodynamic parameters were measured at the same time points.


RESULTS
Plasma osmolality and sodium increased only in the HS group. Changes in plasma BNP and ANP levels did not differ between the groups (P=0.212 and 0.356). There were no correlations between NP levels and osmolality or sodium at any time point. In the HS group, urine volume was higher (3295 vs. 2644 ml; P<0.05) and the need for furosemide treatment was less (0.4 vs. 3.8 mg; P<0.01) than in the HES group.


CONCLUSIONS
The absence of effects of plasma sodium content or hyperosmolality on NP release validates the value of NPs as a biomarker in peri-operative patients.