Up to 50% of all patients requiring cardiopulmonary bypass during cardiac surgery develop acute renal failure, with less than 5% requiring renal replacement therapy. Consequently, post-cardiac surgery acute kidney injury (AKI) is associated with increased morbidity and mortality. In the July Critical Care Medicine, McGuinness and colleagues designed a multicenter Phase IIb trial to test the hypothesis that a perioperative infusion of sodium bicarbonate might attenuate AKI in cardiac surgery patients.
This study was a multicenter, double-blind, randomized controlled trial designed to assess whether an infusion of sodium bicarbonate versus an infusion of 0.9% sodium chloride would result in less postoperative AKI in patients undergoing cardiac surgery. Patients were included if they were considered to be a higher risk for postoperative AKI based on previously published predictive criteria. The primary outcome was postoperative AKI; secondary outcomes included the need for dialysis, degree of AKI (based on Risk, Injury, Failure, Loss, and End-Stage kidney disease [RIFLE] and Acute Kidney Injury Network [AKIN] criteria), and additional clinical and physiological outcomes. Data were analyzed according to the intention-to-treat principle with appropriate univariate and multivariate statistics.
After 433 patients were enrolled, 218 patients received sodium bicarbonate and 215 received sodium chloride. Three patients were lost before analysis in each group. Patients who received sodium bicarbonate had statistically higher blood pH, blood bicarbonate, and urine pH when followed for 24 hours. There was no difference in the incidence of AKI between the study groups. The bicarbonate group, 47% of patients (95% confidence interval [CI] =, 40%-55%) developed AKI compared to 44% (95% CI, 37%-51%) in the sodium chloride group (P=0.58). The overall need for dialysis was 3% in the bicarbonate group and 5% in the sodium chloride group (P=0.44). No differences were found for other secondary outcomes. As an additional finding, previously published preoperative criteria for the prediction of AKI after surgery appeared to be validated by this study.
This study exhibited the strengths of a sound design, including double blinding and multicenter international enrollment. The study was stopped prematurely before full enrollment (based on preliminary results communicated to the investigators from another concomitant similar trial), and it is possible that the study might have been underpowered due to an underestimation of the control event rate of AKI in the normal saline group (type 2 error). Moreover, different cardiopulmonary bypass and other practices among the participating institutions may have introduced some degree of residual confounding. Despite these limitations and others, the results from this study provide the most current and best available evidence to date suggesting that perioperative sodium bicarbonate does not reliably reduce AKI following cardiac surgery in high-risk patients.
This Concise Critical Appraisal is authored by SCCM member Samuel M. Galvagno Jr., DO, PhD.
Galvagno is an Assistant Professor at the University of Maryland, R. Adams Cowley Shock Trauma Center, and is board certified in anesthesiology, critical care medicine, and public health. He earned his PhD in Clinical Investigation from Johns Hopkins in 2012. His major interests include aeromedical critical care, pain management in the ICU, medical education, and patient safety. He teaches FCCS, ACLS, PALS, and ATLS. A major in the United States Air Force, he is the Director of Critical Care Air Transport Team (CCATT) Operations at the 943rd Aerospace Medicine Squadron at the 943rd Rescue Group, Davis-Monthan Air Force Base, Arizona.