Recovery after Acute Kidney Injury

Abstract

Rationale: Little is known about how acute kidney injury (AKI) resolves, and whether patterns of reversal of renal dysfunction differ among patients with respect to ultimate recovery.

Objectives: We sought to examine different patterns for AKI reversal that are found in patients and assess how they relate to postdischarge outcomes.

Methods: We studied 16,968 critically ill patients with Kidney Disease Improving Global Outcomes stage 2 or 3 AKI, using an electronic database. Reversal of AKI was defined as alive and no longer meeting criteria for even stage 1. Recovery was defined as reversal at hospital discharge.

Measurements and main results: We observed five patterns. The most common (4,508; 26.6%) was early reversal that was sustained through discharge, but almost as many patients (4,496; 26.5%) had no reversal at all. The remaining patients had late reversal after Day 7 (9.7%); early reversal with one or more relapses, but with ultimate recovery (22.5%); and relapsing without recovery (14.7%). Outcomes for patients with these phenotypes were quite different, with age-adjusted 1-year survival varying from more than 90% for early reversal to less than 40% for patients never reversing. Relapses are common (37.3%), especially in the first 72 hours after reversal, and are associated with a fivefold increased risk for death by 1 year compared with early sustained reversal.

Conclusions: We have identified five distinct recovery phenotypes on the basis of the clinical course over the first week after AKI manifestation. These phenotypes may identify patients amenable to therapeutic intervention. Long-term outcomes are associated with recovery status at hospital discharge.

Keywords: critical care; dialysis; outcomes; renal failure; survival.

Figure 1.

Conceptual model. Acute kidney injury (AKI) is an abrupt loss of renal function developing over the course of 7 days or less (1). Although the actual start of AKI may not be identified (more than half of AKI cases are community acquired), and many cases may not resolve rapidly, we defined “early reversal” as absence of AKI for at least 24 hours within 7 days of first documented AKI. *Recovery status was determined at hospital discharge, but we recognize that recovery may proceed out further, and a true final status would be better assessed at 90 days or longer.

Figure 2.

Study flow. Source population included all patients admitted to the intensive care unit (ICU). *Exclusions: not stage 2 or 3 acute kidney injury (23,587); end-stage kidney disease, creatinine >3.5 or receiving dialysis before ICU admission (3,839); massive blood transfusion (1,174); ICU stay <48 hours (3,631).

Figure 3.

Age-adjusted survival by recovery patterns. Survival differences are highly significant overall (P < 0.001). All pairwise comparisons are also significant. For example, late sustained reversal versus relapse recovery hazard ratio (95% confidence interval): 0.86 (0.77–0.96), P = 0.005; relapse with no recovery versus never reversed hazard ratio (95% confidence interval): 0.81 (0.76–0.86), P < 0.001. ICU = intensive care unit; RRT = renal replacement therapy.