LAUSR

We thank Prof. Xue and colleagues for their interest [letter ref] in our observational study on associations between mean systemic filling pressure and acute kidney injury (AKI) following elective cardiac surgery [2]. To be precise, we have not argued that calculating the mean systemic filling pressure analogue (Pmsa ) provides a surrogate for renal venous pressure. We have proposed that Pmsa represents a closer physiological approximation of the renal venous pressure compared to central venous pressure (CVP). This is by virtue of representing the distending pressure within the entire intravascular compartment, particularly influenced by changes in splanchnic vascular compliance, and the 'upstream' anatomical proximity of the renal vessels on the Pmsa -CVP pressure gradient for venous return in the inferior vena cava.