Effects of acute plasma volume expansion on renal perfusion, filtration, and oxygenation after cardiac surgery: a randomized study on crystalloid vs colloid

Background In the present randomized study, we evaluated the differential effects of a colloid and a crystalloid fluid on renal oxygen delivery ( R D O 2 ), glomerular filtration (GFR), renal oxygen consumption ( R V ˙ O 2 ), and the renal oxygen supply–demand relationship (i.e. renal oxygenation) after cardiac surgery with cardiopulmonary bypass. Methods Thirty patients with normal preoperative renal function, undergoing uncomplicated cardiac surgery, were studied in the intensive care unit in the early postoperative period. Patients were randomized to receive a bolus dose of either a crystalloid (Ringers-acetate® 20 ml kg−1, n=15) or a colloid solution (Venofundin® 10 ml kg−1, n=15). Systemic haemodynamics were measured via a pulmonary artery catheter. Renal blood flow and GFR were measured by the renal vein retrograde thermodilution technique and by renal extraction of 51Cr-EDTA (=filtration fraction). Arterial and renal vein blood samples were obtained for measurements of renal oxygen delivery ( R D O 2 ) and R V ˙ O 2 . Renal oxygenation was estimated from the renal oxygen extraction. Results Despite an increase in cardiac index and renal blood flow with both fluids, neither of the fluids improved R D O 2 , because they both induced haemodilution. The GFR increased in the crystalloid (28%) but not in the colloid group. The crystalloid increased the filtration fraction (24%) and renal oxygen extraction (23%), indicating that the increase in GFR, the major determinant of R V ˙ O 2 , was not matched by a proportional increase in R D O 2 . Conclusions Neither the colloid nor the crystalloid improved R D O 2 when used for postoperative plasma volume expansion. The crystalloid-induced increase in GFR was associated with impaired renal oxygenation, which was not seen with the colloid. Clinical trial registration NCT01729364.