Risk and outcome analysis of renal replacement therapies in patients after cardiac surgery with pre-operatively normal renal function

Peri-operative acute renal failure requiring renal replacement therapy is common (5-30%) after cardiac surgery and associated with a mortality of similar to 50%. Pre-operative renal impairment seems to be the most important risk factor for frank postoperative renal failure. To help evaluate the risk factors, we conducted a prospective observational trial of 1574 consecutive patients with normal pre-operative renal function (creatinine < 110 mu mol.l(-1)). Renal failure was defined as the need for renal replacement therapy. After univariate analysis of previously described risk factors, those who differed significantly between patients with or without renal failure were enrolled into a multi-variate classification and regression tree (CART) statistical model that identifies the most 'predictive' risk factors and creates a ranked list of these. In patients with pre-operatively normal renal function, a serum level of lactate > 1.1 mmol.l(-1) in the first 24 h after the operation was the strongest predictor for the development of renal failure.