DURATION OF HYPOTENSION IS A PREDICTOR OF ACUTE KIDNEY INJURY IN THE POST-CARDIAC SURGERY PATIENT.

Abstract

<h3>Objectives</h3> Post-operative hypotension is a common problem for any patient undergoing major surgery. It has been thoroughly evaluated in the non-cardiac surgical cohort and is associated with increased risk of myocardial infarction, acute kidney injury (AKI) and mortality (1,2,3). However, the nature of the post-operative hypotension and its implications in the cardiac surgery cohort have not been well described. Our objective is to better describe this cohort of patients, to describe the frequency and duration of hypotension in the first 12 hours after cardiac surgery in the intensive care unit and its relationship to patient-centred outcomes. <h3>Design and Method</h3> A retrospective study of consecutive adult cardiac surgical patients requiring intra-operative cardiopulmonary bypass over a 10-week period at a tertiary teaching hospital in London, UK. Demographic and baseline data were collected for each patient in addition to post-operative adverse events and then compared with continuous arterial blood pressure monitoring data for the first 12 hours after arrival in the ICU after surgery. Any relationship between hypotension and subsequent outcome was explored. Hypotension was defined as a mean arterial pressure (MAP) <65 and severe hypotension as MAP <50 lasting for at least a minute. Multivariate regression analysis was carried out to identify correlation between hypotension and subsequent complications. <h3>Results</h3> A total of 51 cases were included with a broad case mix (69% coronary artery bypass graft (CABG), 11.5% aortic valve surgery, 5.8% mitral valve surgery, 7.7% CABG plus valve surgery and 5.8% other). Average age was 64.5 years and 73.6% of patients were male. Average Euroscore II was 1.60. On average, patients experienced 10 hypotensive events with a total duration of hypotension of 79.7 minutes. The average duration of each hypotensive event was 6.7 minutes. 47.1% of patients experienced severe hypotension with an average duration of 2.3 minutes. To address this hypotension, patients received on average 2188ml of intravenous (IV) crystalloid solution in the first 6 hours and a further 578ml in the subsequent 6 hours resulting in an average cumulative fluid balance at 12 hours of 1591ml, in addition to vasopressors. The duration of the hypotensive event predicted subsequent AKI with OR 1.02 (95% CI 1.00 – 1.04, p=0.053). Hypotension was not correlated with respiratory, hepatic or neurological complications post-operatively. It was also not correlated with ICU or hospital length of stay. <h3>Conclusions</h3> Whilst it has been previously proven that post-operative hypotension increases the complication rate generally, this study suggests that the duration of hypotensive events in the post-cardiac surgical patient appears to be a predictor for developing an acute kidney injury which, to our knowledge, has not been described before in this patient cohort. Not only is this hypothesis-generating for future studies, but it also suggests that the use of hypotension-predicting technologies could perhaps improve speed of treatment thereby decreasing the duration of hypotension and subsequently decreasing the rate of AKI after major cardiac surgery.