Cystatin C: influence of perfusion and myocardial injury on early (<24 h) renal function after pediatric cardiac surgery

Background: Cardiopulmonary bypass (CPB)-associated renal dysfunction following cardiac surgery is well recognized. In patients with renal disease, cystatin C has emerged as a new biomarker which in contrast to creatinine (Cr) is sensitive to minor changes in glomerular filtration rate (GFR). Aim: We utilized cystatin C to investigate the association of CPB perfusion parameters with acute renal injury after pediatric cardiac surgery. Methods: Twenty children, aged 4-58 months (AVSD, n = 7; VSD, n = 9; and ASD, n = 4), were prospectively studied. Glomerular filtration rate was quantified postoperatively by creatinine clearance (first and second 12-h periods; CrCl _0-12 and CrCl _12-24). Serum cystatin C and Cr were measured preoperatively and on days 0-3. Recorded CPB parameters included bypass duration (BP), perfusion pressure (PP), lowest pump flow (Q _min), lowest hematocrit, and corresponding lowest oxygen delivery (DO _{2 min}). Myocardial injury was determined by troponin-I. Results: Postoperatively, GFR remained unchanged (CrCl _0-12 63.6 ± 37.0 vs CrCl _12-24 65.1 ± 27.5; P = 0.51) and only correlated with cystatin C (CrCl _0-12 vs cystatin C _Day0 [r = 0.58, P = 0.018] and Cr _Day0 [r = 0.09, P = 0.735]). Cr and cystatin C increased postoperatively to peak on days 2 and 3, respectively (Cr _PreOp 31 ± 6.9 vs Cr _Day2 36.9 ± 12.2, P = 0.03; cystatin C _Day0 0.83 ± 0.27 vs cystatin C _Day3 1.45 ± 0.53, P = 0.02). Increased cystatin C was significantly associated with BP (P = 0.001), mean PP (P = 0.029), Q _min (P = 0.005), troponin-I (P < 0.001), and DO _2min <300 ml·min ^-1·m ^-2 (P = 0.007). Receiver-operator cutoff >1.044 mg·l ^-1 for cystatin C exhibited 100% sensitivity and 67% specificity for detecting renal dysfunction, defined as GFR <55 ml·min ^-1·1.73 m ^-2. Conclusions: Cystatin C is a sensitive marker of early renal dysfunction following pediatric heart surgery. Variations in bypass parameters, myocardial injury, and ultimately critical oxygen delivery are significantly associated with the degree of renal impairment.