A prospective observational study of early changes in plasma renin concentrations and associations with complications following cardiac surgery

Background. Increased plasma renin concentrations have been reported in patients following cardiac surgery while correlations to clinical outcomes have varied. More evidence is needed to support the potential clinical utility of plasma renin as a biomarker guiding postoperative management, including the need for alternative pharmacotherapy when standard catecholaminergic cardiovascular support is insufficient Methods. Plasma concentrations were determined by direct renin immunoassay (milli-International Units per litre, mIU.l ^− 1 ) on admission to ICU and then six and 24 hours later. Postoperative complications were assessed by the composite and separate incidence of acute kidney injury, acute myocardial infarction, shock, acute respiratory failure, new onset atrial flutter/fibrillation and cerebrovascular accident. Pharmacological support required to treat postoperative haemodynamic instability was quantified using the vasoactive-inotropic score. Results. 104 patients were studied and 54 (52%) met at least one diagnostic criterion for postoperative complications. Renin concentrations on admission (130 [34–445] mIU.l ^− 1 ) and six (119 [35–447] mIU.l ^− 1 ) and 24 hours later (184 [54–513] mIU.l ^− 1 ) were not significantly different with substantial inter-individual variation. Cumulative renin concentrations over 24 hours were higher in haemodynamically unstable patients (median difference 1296 [54-2943] mIU.l ^− 1 , p = 0.04) and in patients with any postoperative complication (median difference 1887 [908–6177] mIU.l ^− 1 , p = 0.04). Plasma renin increased by 11 mIU.l ^− 1 for each unit increase in the vasoactive-inotropic score. A statistical model using all renin measurements predicted haemodynamic instability (AUC 0.77 [0.55–0.95], p = 0.04) and shock (AUC 0.95 [0.83-1.0], p = < 0.001), but not the composite or separate incidence of the other complications. Conclusions. Haemodynamic compromise in postoperative cardiac patients could be predicted using serial plasma renin concentrations measured during the first 24 hours of ICU admission, supporting the potential role of renin as a biomarker for targeted haemodynamic management. Additional prospective studies are warranted to elucidate the relationship between renin dynamics, postoperative complications, and to establish evidence-based criteria for escalating vasopressor therapy. Trial registration: ClinicalTrials.gov NCT043303455 (registered 8 March 2020)