Using urinary biomarkers to reduce acute kidney injury following cardiac surgery

Abstract

Background: Prediction of acute kidney injury (AKI) following cardiac surgery is unreliable through the use of serum creatinine or urinary output alone. Cell cycle arrest urinary biomarkers insulin-like growth factor-binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinases-2 (TIMP2) provide early detection of kidney stress and possibly AKI. We sought to determine whether therapeutic interventions driven by elevated urinary biomarkers (UB) reduces post-cardiac surgery stage 2/3 AKI.

Methods: A quality improvement initiative based on UB was undertaken in all adult on-pump cardiac surgical patients with a preoperative serum creatinine level ≤2.0 mg/dL. A UB score the morning after cardiac surgery that was considered positive for kidney stress (≥0.3 [ng/mL]²/1000) triggered activation of a multidisciplinary acute kidney response team (AKRT) with implementation of a predefined staged protocol, including targeted goal-directed fluid management, liberalized transfusion thresholds, continued invasive hemodynamic monitoring and its optimization in the intensive care unit, and avoidance of nephrotoxins. We compared the incidence of stage 2/3 AKI before (pre-UB) versus after (post-UB) implementation of the Kidney Disease: Improving Global Outcomes quality improvement initiative. Standardized, protocolized, evidence-based care pathways were used pre-UB.

Results: The incidence of stage 2/3 AKI was compared in 435 pre-UB patients and 412 post-UB patients. Fifty-five percent of the post-UB patients had a moderate or high UB score (≥0.3 [ng/mL]²/1000). Ten patients (2.30%) had stage 2/3 AKI pre-UB, compared with 1 patient (0.24%) post-UB, a relative reduction of 89% (P = .01). The total and postoperative lengths of stay, cost, mortality, and readmissions were similar in the 2 groups. The negative predictive value for AKI of UB <0.3 [ng/mL]²/1000 was 100%.

Conclusions: The routine measurement of UB and subsequent activation of an AKRT are useful post-cardiac surgery therapeutic adjuncts. They are associated with early detection of kidney stress, allowing for targeted proactive intervention, and a significant decrease in postoperative stage 2/3 AKI without increases in cost or length of stay.

Keywords: acute kidney injury; biomarkers; critical care; perioperative care; quality improvement.