The effect of ‘renal-dose ’ dopamine on renal tubular function following cardiac surgery: assessed by measuring retinol binding protein (RBP)1

Objective: Acute renal failure complicating open heart surgery is not uncommon. Dopamine infusion (2.5–4.0 mg/kg per min) has often been advocated for prophylactic ‘renal protection ’ in this setting despite little objective evidence of real benefit. We aimed to investigate whether dopamine offers any ‘renal protection ’ in patients with normal heart and kidney functions undergoing routine coronary artery bypass grafting (CABG). Urinary excretion of retinol-binding protein (RBP), previously validated as a sensitive and accurate marker of early renal tubular injury, was used to assess the renal effects of dopamine during the first postoperative week. Methods: Forty consecutive patients from the elective waiting list were prospectively randomized into two equal groups: those in Group A received dopamine infusion at ‘renal dose ’ (2.5–4.0 mg/kg per min) starting from induction of anaesthesia for 48 h, whereas those in Group B served as untreated controls. Daily measurements were made of weight-adjusted urine output (ml/kg), fluid balance (input/output), serum creatinine, blood urea and urinary RBP. Statistical comparisons were made using Mann–Whitney U-test. Results: The two groups matched in terms of age, time and temperature on cardiopulmonary bypass, number of grafts performed and perioperative haemodynamic status. No differences were detected in the weight-adjusted urine output, fluid balance, serum creatinine and blood urea between the groups. Control subjects (Group B) showed an increase in urinary RBP during the first and second postoperative days (323 – 4 mg/ mmolCr and 50 – 3 mg/mmolCr; mean – SD). However, patients treated with dopamine (Group A) demonstrated much greater urinary excretion of RBP over the same period (1257 – 15 mg/mmolCr and 449 – 21 mg/mmolCr; P = 0.0006 and 0.03) than those in Group B