Early serum creatinine accurately predicts acute kidney injury post cardiac surgery

Acute Kidney Injury (AKI) is a well recognized complication of cardiac surgery. It is associated with significant morbidity and mortality. The aims of our study are twofold; 1. To define the incidence of AKI post cardiac surgery. 2. To identify pre-morbid and operative risk factors for developing AKI and to determine if immediate post operative serum creatinine (IPOsCr) accurately predicts the development of AKI.

We prospectively studied 196 consecutive patients undergoing elective (on-pump) cardiac surgery. Baseline patient characteristics, including medical co-morbidities, proteinuria, procedural data and kidney function (serum creatinine (sCr) were collected. Internationally standardised criteria for AKI were used (sCr >1.5 times baseline, elevation in sCr >26.4 μmmol/L (0.3 mg/dl). Measurements were collected pre-operatively, within 2 h of surgical completion (IPOsCr) and daily for two days. Logistic regression was used to assess predictive factors for AKI including IPOsCr. Model discrimination was assessed using ROC AUC curves.

Forty (20.4%) patients developed AKI postoperatively. Hypertension (OR 2.64, p = 0.02), diabetes (OR 2.25, p = 0.04), proteinuria (OR 2.48, p = 0.02) and a lower baseline eGFR (OR 0.74, p = 0.002) were associated with AKI in univariate analysis. A multivariate logistic model with preoperative and surgical factors (age, gender, eGFR, proteinuria, hypertension, diabetes and type of cardiac surgery) demonstrated moderate discrimination for AKI (ROC AUC 0.76). The addition of IPOsCr improved model discrimination for AKI (AUC 0.82, p = 0.07 versus baseline AUC) and was independently associated with AKI (OR 7.17; 95% CI 1.27-40.32; p = 0.025).

One in 5 patients developed AKI post cardiac surgery. These patients have significantly increased morbidity and mortality. IPOsCr is significantly associated with the development of AKI, providing a cheap readily available prognostic marker.