Renal hypoxanthine balance in cardiac surgery: Effects of felodipine

Objective: To test the hypothesis that felodipine, a renal vasodilator, can prevent a release of hypoxanthine during rewarming after moderate hypother mic cardiopulmonary bypass and that this is related to improved renal oxyge n supply. Design: A prospective, randomized, and controlled study. Setting: Operating room in the cardiothoracic surgery department of a unive rsity hospital. Participants: Twenty-two patients submitted to elective first-time coronary bypass surgery. Interventions: A catheter was placed in the left renal vein for thermodilut ion renal blood flow (RBF) measurement and blood sampling. In 11 patients, felodipine was infused during the hypothermic period of cardiopulmonary byp ass. Measurements and Main Results: Renal uptake (renal arteriovenous concentrat ion difference x RBF) of hypoxanthine was maintained during rewarming in fe lodipine-treated patients but not in control patients (55 +/- 28 v -39 +/- 1 nmol/min, p < 0.05). Oxygen consumption was higher after felodipine infus ion despite unchanged total RBF. A positive correlation between renal oxyge n consumption and hypoxanthine uptake and release (r = 0.74, p < 0.01) was observed. Conclusions: Felodipine maintained renal uptake of hypoxanthine during rewa rming after hypothermic cardiopulmonary bypass. This maintenance is the eff ect of improved renal oxygen supply secondary to improved nutritive blood f low at the expense of nonnutritive renal blood flow. Copyright (C) 1999 by W.B. Saunders Company.