BNP (Nesiritide) vs. Placebo to Protect Kidney Function in Patients Undergoing Heart Bypass Surgery.

• Creatinine Clearance at 72 hours determined by the Cockroft-Gault formula [ Time Frame: 72 hours post op ] [ Designated as safety issue: No ]
  

• Number of patients requiring dialysis during the hospitalization [ Time Frame: before hospital discharge ] [ Designated as safety issue: No ]
  
• Plasma aldosterone levels at 12 hours and 24 hours [ Time Frame: 12 hours and 24 hours postoperatively ] [ Designated as safety issue: No ]
  
• Total time on ventilator, ICU length of stay, total length of stay in hospital [ Time Frame: total length of hospital stay ] [ Designated as safety issue: No ]
  
• pre and postoperative diuretic dose used [ Time Frame: pre operative and postoperate ] [ Designated as safety issue: No ]
  
• Need or absence of need for inotropic support in the 72 hour perioperative period [ Time Frame: 72 hours perioperative ] [ Designated as safety issue: No ]
  

Drug: Neseritide
Dose of Nesiritide infusion will be 0.005 ug/Kg/min
Other Name: BNP, Nesiritide

This is a randomized, double-blind, placebo controlled study of low dose nesiritide to prevent renal insufficiency after cardiopulmonary bypass surgery. Patients included are those with greater than mild renal insufficiency preoperatively as defined by having a creatinine clearance of less than 50 mL/minute determined by the Cockroft-Gault formula. The infusion of nesiritide (BNP) 0.005 mcg/Kg/minute or placebo begins 1 hour before surgery and runs for 24 hours started after the induction of anesthesia prior to cardiopulmonary bypass.