Oxygen Delivery During Cardiopulmonary Bypass and Acute Renal Failure After Coronary Operations

Background The degree of hemodilution during cardiopulmonary bypass has recently been identified as an independent risk factor for acute renal failure after cardiac operations. In this prospective observational study we have investigated the role of the lowest oxygen delivery, lowest hematocrit, and pump flow during cardiopulmonary bypass as possible risk factors for acute renal failure and renal dysfunction. Methods One thousand forty-eight consecutive patients undergoing coronary operations have been studied. For each patient we have recorded the lowest hematocrit on cardiopulmonary bypass, the correspondent lowest oxygen delivery, and the pump flow around the time of these determinations. The three variables have been explored in a multivariable model as possible risk factors for acute renal failure and postoperative serum creatinine levels increase. The role of transfusions in determining acute renal failure was subsequently included in the model. Results The best predictor for acute renal failure and peak postoperative serum creatinine levels was the lowest oxygen delivery, with a critical value at 272 mL • min−1 • m−2. The lowest hematocrit was an independent risk factor with a lowest predictive value at a cutoff of 26%. When corrected for the need for transfusions, only the lowest oxygen delivery remained an independent risk factor. Conclusions A high degree of hemodilution during cardiopulmonary bypass is a risk factor for postoperative renal dysfunction; however, its detrimental effects may be reduced by increasing the oxygen delivery with an adequately increased pump flow.