Preoperative serum brain natriuretic peptide and risk of acute kidney injury after cardiac surgery

Abstract

Background: Acute kidney injury (AKI) after cardiac surgery is associated with poor outcomes and is difficult to predict. We conducted a prospective study to evaluate whether preoperative brain natriuretic peptide (BNP) levels predict postoperative AKI among patients undergoing cardiac surgery.

Methods and results: The Translational Research Investigating Biomarker Endpoints in Acute Kidney Injury (TRIBE-AKI) study enrolled 1139 adults undergoing cardiac surgery at 6 hospitals from 2007 to 2009 who were selected for high AKI risk. Preoperative BNP was categorized into quintiles. AKI was common with the use of Acute Kidney Injury Network definitions; at least mild AKI was a ≥0.3-mg/dL or 50% rise in creatinine (n=407, 36%), and severe AKI was either a doubling of creatinine or the requirement of acute renal replacement therapy (n=58, 5.1%). In analyses adjusted for preoperative characteristics, preoperative BNP was a strong and independent predictor of mild and severe AKI. Compared with the lowest BNP quintile, the highest quintile had significantly higher risk of at least mild AKI (risk ratio, 1.87; 95% confidence interval, 1.40-2.49) and severe AKI (risk ratio, 3.17; 95% confidence interval, 1.06-9.48). After adjustment for clinical predictors, the addition of BNP improved the area under the curve to predict at least mild AKI (0.67-0.69; P=0.02) and severe AKI (0.73-0.75; P=0.11). Compared with clinical parameters alone, BNP modestly improved risk prediction of AKI cases into lower and higher risk (continuous net reclassification index; at least mild AKI: risk ratio, 0.183; 95% confidence interval, 0.061-0.314; severe AKI: risk ratio, 0.231; 95% confidence interval, 0.067-0.506).

Conclusions: Preoperative BNP level is associated with postoperative AKI in high-risk patients undergoing cardiac surgery. If confirmed in other types of patients and surgeries, preoperative BNP may be a valuable component of future efforts to improve preoperative risk stratification and discrimination among surgical candidates.

Trial registration: ClinicalTrials.gov NCT00774137.

Figure 1

The relationship between serum BNP and AKI (at least mild AKI, panels A and B; severe AKI, panels C and D) by spline regression modeling. Serum BNP was log-transformed in B and d. The curves represent restricted cubic splines with knots estimated by the arrows on the abscissa. Triangles denote the empirical logits. Abbreviations: Acute kidney injury (AKI), brain natriuretic peptide (BNP)

Figure 2

Incidence of At Least Mild AKI (a) and Severe AKI (b) by Quintiles of Pre-operative BNP. AKI defined as during entire hospitalization, at least mild AKI (A) defined as ≥50%, ≥0.3 mg/dL or dialysis; severe AKI (B) defined as ≥100% or dialysis. BNP measured in pg/mL. Abbreviations: Acute kidney injury (AKI), brain natriuretic peptide (BNP)

Figure 3

Reclassification Plot of Predicted Probabilities of At Least Mild AKI Based on the Clinical Model with and without Pre-operative BNP, by AKI status. Predicted risks for at least mild AKI according to the clinical model (x-axis) and according to the clinical model with pre-op serum BNP included (y-axis) for AKI cases (panel A; red) and non-cases (panel B; blue). The diagonal line indicates a line of identity, such that for points above this line the predicted risk is higher in the new model (improved reclassification for AKI cases) and for points below this line the predicted risk is lower (improved reclassification for non-AKI cases). Abbreviations: Acute kidney injury (AKI); brain natriuretic peptide (BNP)

Figure 4

Incidence of At Least Mild AKI (a) and Severe AKI (b) by Quintiles of Post-operative BNP. AKI defined as during entire hospitalization, at least mild AKI (A) defined as ≥50%, ≥0.3 mg/dL or dialysis; severe AKI (B) defined as ≥100% or dialysis. Post-operative BNP levels (pg/mL) were measured 0–6 hours following cardiac surgery (mean 0.6 h, SD1.6 h). Abbreviations: Acute kidney injury (AKI); brain natriuretic peptide (BNP)