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A nonselective extracorporeal blood purification (EBP) device connected to the cardiopulmonary bypass circuit during surgery reduced the risk of cardiac surgery-associated acute kidney injury (CSA-AKI), a randomized trial found.

Within 7 days of undergoing nonemergent cardiac surgery, 28.4% of patients in the EBP group experienced CSA-AKI compared with 39.7% in the standard care group. The adjusted 10.4% difference (95% CI 2.3-18.5, P=0.01) met prespecified criteria for a "clinically important difference," reported researchers led by Xosé Pérez-Fernández, PhD, MD, of the Universitat de Barcelona in Spain, in .

There were no significant differences for most clinical secondary endpoints or in adverse events. Findings from the double-blind SIRAKI02 study were simultaneously presented at the European Society of Intensive Care Medicine's in Barcelona.

AKI after cardiac surgery occurs in around 10% to 40% of patients, Pérez-Fernández and co-authors pointed out. The condition is tied to prolonged length of stay, increased costs, and increased hospital mortality. While most cases resolve, indicate that approximately 11% of patients will develop acute kidney disease and 6% will progress to chronic kidney disease (CKD) after a year.

"Although the major area of focus for these EBP devices has been sepsis, there has been interest in using these devices in the context of cardiac surgery-associated AKI given the systemic inflammatory response that occurs during cardiopulmonary bypass, as well as the fixed timing of the cardiac surgery insult," said Yuenting Diana Kwong, MD, and Kathleen Liu, MD, PhD, both of the University of California San Francisco, in an .

Despite the benefit of EBP observed in the current trial, "most of the AKI episodes were early, transient, mild, and appear to be identified by urine output rather than creatinine criteria," they noted, and "there was no benefit on longer-term secondary outcomes, with very limited to no signal of potential benefit."

In the EBP group, patients received treatment during the cardiopulmonary bypass with a nonselective acrylonitrile-sodium methallylsulfonate/polyethylenimine membrane (oXiris) connected to a continuous kidney replacement therapy machine. The continuous kidney replacement therapy modality used was slow continuous ultrafiltration. Perfusionists were allowed to remove fluid from the patient if clinically required.

More patients in the EBP group had ultrafiltration (24% vs 12%), though the volume of fluid removed was higher in the standard care group. The editorialists commented that in theory, "ultrafiltration may affect AKI parameters by changing volume status and the volume of distribution of creatinine." However, AKI rates remained significantly lower with EBP even after excluding those receiving ultrafiltration (29% vs 41%, P=0.03).

"In subgroup analyses, those with CKD, diabetes, hypertension, heart failure, and low body mass index were more likely to benefit from the intervention," noted Kwong and Liu.

A total of 343 patients were randomized in the double-blind trial conducted at two Spanish tertiary hospitals' operating rooms and intensive care units (ICUs). This included 169 patients who received EBP and 174 who received usual care. Patients with advanced CKD (stages 4 or 5) were excluded. Average age was 69 and a third were female. Baseline characteristics of the groups were similar, other than more statin and aspirin use in the EBP group.

For the most part, the "patients were receiving double or triple valve replacement or coronary artery bypass grafting (CABG) plus valve replacement or ascending aortic replacement plus CABG/valve replacement," said Pérez-Fernández and colleagues.

AKI was defined by Kidney Disease Improving Global Outcomes criteria based on serum creatinine increase and/or urine output decrease. While all individual grades of CSA-AKI were lower with the EBP device, the differences were not significantly different. The worst CSA-AKI category within 7 days of surgery was recorded for each patient:

• CSA-AKI I: 15% with EBP vs 20% with standard care
• CSA-AKI II: 10% vs 14%
• CSA-AKI III: 3% vs 6%
• CSA-AKI II/III: 13% vs 20%

Fewer patients in the EBP group required kidney replacement therapy (1.8% vs 3.5%), and differences in peak serum creatine level (1.26 vs 1.39 mg/dL) and oliguria for more than 6 hours favored EBP (13% vs 20%), but none reached statistical significance. Slightly fewer EBP patients experienced transitory AKI (within the first 48 hours), but slightly more experienced persistent AKI (>48 hours).

Surgical complications and complications occurring during stays in the ICU were comparable between the groups. Median ICU stay was 3 days for both groups. And there were no significant differences in survival measured out to 90 days.

Pérez-Fernández's group said the true rate of CSA-AKI among patients transferred out of the ICU is unknown since urine output was not accurately collected during the full 7 postoperative days. Other limitations were a lack of data on some variables like cytokines or creatinine after discharge from the ICU.

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