Duration of acute kidney injury impacts long-term survival after cardiac surgery

Abstract

Background: Acute kidney injury (AKI) after cardiac surgery is associated with worse outcomes. However, it is not known how adverse long-term consequences vary according to the duration of AKI. We sought to determine the association between duration of AKI and survival.

Methods: Medical records of 4,987 cardiac surgery patients from 2002 through 2007 with serum creatinine (SCr) collection at a medical center in northern New England were reviewed. Acute kidney injury was defined as at least a 0.3 (mg/dL) or at least a 50% increase in SCr from baseline and further classified into AKI Network stages. Duration of AKI was defined by the number of days AKI was present and categorized as no AKI and AKI for 1 to 2, 3 to 6, and at least 7 days.

Results: Thirty-nine percent of patients exhibited AKI. Long-term survival was significantly different by AKI duration (p < 0.001). The proportion of patients with AKI duration, adjusted hazard ratio, and 95% confidence interval for mortality (no AKI as referent) were as follows: 1 to 2 days (18%; adjusted hazard ratio, 1.66; 95% confidence interval, 1.32 to 2.09), 3 to 6 days (11%; adjusted hazard ratio, 1.94; 95% confidence interval, 1.51 to 2.49), ≥7 days (9%; adjusted hazard ratio, 3.40; 95% confidence interval, 2.73 to 4.25). This graded relationship of duration of AKI with long-term mortality persisted when patients who died during hospitalization were excluded from analysis (p < 0.001). Propensity-matched analysis confirmed results.

Conclusions: The duration of AKI after cardiac surgery is directly proportional to long-term mortality. This AKI dose-dependent effect on long-term mortality helps to close the gap between association and causation, whereby AKI stages and AKI duration have important implications for patient care and can aid clinicians in evaluating the risk of in-hospital and postdischarge death.

Figure 1. Duration of AKI

The duration of AKI is plotted with the proportion of resolved AKI on the y-axis and days to AKI recovery on the abcissa. The insert is a magnification of the data for the first 30-days.

Figure 2. Survival by Duration of AKI

The proportion of patients surviving from the time of cardiac surgery is plotted by the categories for the duration of AKI: no AKI (grey line), AKI for 1–2, 3–6, and ≥7 days (black lines, Log rank p-value <0.001)

Figure 3. Survival by Transient and Persistent AKI

The proportion of patients surviving from the time of cardiac surgery is plotted by no AKI (grey line), transient AKI (grey dotted lines: resolved AKI by the time of discharge lasting for 1–2, 3–6, and ≥7 days, respectively), persistent AKI (black line: unresolved AKI at the time of discharge), and acute dialysis (bottom black line, Log rank p-value <0.001).