Prophylactic administration of bicarbonate to reduce the risk of postcardiac surgery acute kidney injury: end of the road?.

1802 www.ccmjournal. org July 2013 • Volume 41 • Number 7 Acute kidney injury (AKI) after cardiac surgery remains a vexing problem in hospitalized patients and is associated with increased morbidity, mortality, and costs of care (1), although the rate of dialysis requiring AKI after surgery is relatively low (usually < 5%). A significant body of literature allows us to assess the risk of postoperative AKI based on preoperative and intraoperative characteristics (2). This information combined with a predefined anticipated renal insult— that is, exposure to cardiopulmonary bypass—makes cardiac surgery an ideal setting to test interventions that can be applied shortly before, during, or soon after the surgical procedure. IV bicarbonate infusion has been used with an intention to offer renal protection in AKI. Several studies have tested this intervention in the clinical setting of contrast-induced nephropathy (CIN). Although individual trials have shown variable results, a meta-analysis of 17 studies (n = 2,633) concluded that CIN risk was significantly attenuated in patients treated with infusion of bicarbonate compared with hydration with sodium chloride (3). The mechanism/pathophysiology of kidney injury in the setting of cardiac surgery is more complex and “multifactorial” compared with the clinical setting of CIN. In addition to the potential for hypoperfusion, there are other factors that pose a risk including 1) inflammatory response as a result of exposure to cardiopulmonary bypass circuit; 2) products of hemolysis due to RBC damage; 3) ischemia-reperfusion injury; and 4) an interplay among the chronic comorbid conditions that predispose patients to kidney damage. Thus, like any other proposed intervention, the role of bicarbonate infusion needs to be evaluated in this surgical setting, not withstanding of its effects in the CIN. Heringlake et al (4) reported a nonrandomized observational experience regarding the use of IV bicarbonate infusion and its effect on renal function in patients undergoing cardiac surgery. A total of 280 patients received 4 mmol/kg of sodium bicarbonate infusion during the observation period and were compared with 304 controls. Although this study did not find any statistically significant difference in the prevalence of AKI across two groups, the analysis did not account for propensity to undergo bicarbonate therapy. Haase et al (5) conducted a prospective randomized double-blind trial comparing infusion of 4 mmol/kg of sodium bicarbonate and 4 mmol/kg of sodium chloride, with 50 patients assigned to each group. The study found a statistically significant difference in the rate of AKI, favoring bicarbonate infusion, when defined as a 25% increase in the serum creatinine level during the postoperative period (p = 0.043). The differences were not statistically significant, however, when AKI was defined as either a 50% or a 100% increase in serum creatinine (p = 0.096 or 0.34, respectively). In this issue of Critical Care Medicine, McGuiness et al (6) report a multicenter double-blind randomized controlled trial comparing the effect of IV sodium bicarbonate with IV normal saline on renal function after cardiopulmonary bypass. Patients in this study received an equimolar concentration of either infusion; patients were given a weight-based bolus over 1 hour after induction of anesthesia, followed by continuous infusion over 23 hours, with a total administered dose of 5.1 mmol/kg body weight. The primary endpoint was defined as either a 25% or a 44 μmol/L increase in serum creatinine level relative to baseline during the first 5 postoperative days. Over a 2-year period, 427 patients were randomized. Overall, 45% of patients reached the primary endpoint (47% in bicarbonate group vs 44% in sodium chloride group; p = 0.58). The authors conclude that bicarbonate infusion did not result in renoprotection as hypothesized. Examination of patient characteristics suggests that this population was fairly representative of patients undergoing cardiac surgery. Although the authors used preoperative risk-assessment models to stratify those patients who were Prophylactic Administration of Bicarbonate to Reduce the Risk of Postcardiac Surgery Acute Kidney Injury: End of the Road? *