ObjectiveTo evaluate the influence of the alpha2-adrenergic receptor agonist clonidine on creatinine clearance as a measure of renal function.DesignProspective, double-blind, randomized, placebocontrolled clinical trial.SettingUniversity hospital.PatientsPatients undergoing coronary artery bypass graft surgery (n equals 48) with normal risk.InterventionsAdministration of clonidine (4 micro gram/kg iv) or placebo 1 hr before induction of anesthesia.Measurements and Main ResultsInduction and maintenance of anesthesia (etomidate, midazolam, and fentanyl) and cardiopulmonary bypass technique (nonpulsatile, normothermic, intermittent cold blood cardioplegia) were standardized in all patients. The night before surgery and the first and third night after surgery, creatinine clearance was calculated from a 12-hr urine collection period. Venous blood samples for determination of plasma anti-diuretic hormone (ADH) concentrations were taken the evening before surgery, immediately before induction of anesthesia and the evening after surgery (n equals 16). Arterial catecholamine plasma concentrations were determined (high-performance liquid chromatography) before induction, 15 mins after induction of anesthesia, immediately after sternotomy, before initiation of cardiopulmonary bypass, as well as 5, 15, and 30 mins after initiation of cardiopulmonary bypass (n equals 16).The total amount of anesthetics, infusions, transfusions, diuresis, and blood loss was not different between the groups. Creatinine clearance decreased over the first postoperative night from 98 plus minus 18 (preoperatively) to 68 plus minus 19 mL/min (p less than .05) in placebo-treated patients. Creatinine clearance remained unchanged in clonidine-treated patients (90 plus minus 19 [preoperatively] to 92 plus minus 17 mL/min). There was a significant difference in creatinine clearance between the groups during the first postoperative night (p less than .05; Mann-Whitney U test). In the third postoperative night, mean creatinine clearance of both groups was not different (75 plus minus 31 vs. 86 plus minus 28 mL/min). ADH concentrations were not different between the groups at any time, while plasma catecholamine concentrations were always significantly lower in clonidine-treated patients.ConclusionsPreoperative treatment with clonidine (4 micro gram/kg) prevents the deterioration of renal function after cardiac surgery. This effect might be due to a clonidine-induced reduction in the sympathetic nervous system response to coronary artery bypass graft surgery.(Crit Care Med 1996; 24:947-952)