Control Group (Open heart surgery alone)

General anesthesia, use of iodine impregnated adhesive dressing, median sternotomy and/or thoracotomy incision, full heparinization (300-400 ui/kg), arterial and venous cannulation, initialization of CPB with or without aortic cross-clamping and high-potassium cold cardioplegia, surgical repair under mild-moderate hypothermia. De-clamping (if cross clamp was applied), neutralization of heparin by protamin, de-cannulation and hemostasis after surgical repair. Insertion of drain(s) and pacing wire(s). Closure of all layers in anatomical plan.

Intraoperative Modified Ultrafiltration (MUF) Group (Open heart surgery with intraoperative MUF)

General anesthesia, use of iodine impregnated adhesive dressing, median sternotomy and/or thoracotomy incision, full heparinization (300-400 ui/kg), arterial and venous cannulation, initialization of CPB with or without aortic cross-clamping and high-potassium cold cardioplegia, surgical repair under mild-moderate hypothermia. De-clamping (if cross clamp was applied), neutralization of heparin by protamin, de-cannulation and hemostasis after surgical repair. Insertion of drain(s) and pacing wire(s). Closure of all layers in anatomical plan.

Once the surgical repair is finished, and CPB will be stopped after aortic declamping. The arterial and venous cannulae will be connected to each other using 3-way connectors and a cardioplegia line. When hemodynamic stability is established (MAP >75 mmHg, CVP > 12 mmHg, Htc > 25%), blood will be drained from the arterial cannula using a roller pump, driven to the ultrafilter, and eventually to the venous cannula. The blood flow will be maintained at ~150 mL/min, and suction will be applied to the filtrate port to achieve an ultrafiltration of 100-120 mL/min. Heat exchanger and bubble trap of the cardioplegia line will be used to maintain the filtered blood at body temperature and to prevent air embolism, respectively. MUF will continue 20 minutes. The filtered volume will be collected.

Preoperative Hemodialysis Group (Open Heart Surgery after preoperative hemodialysis)

General anesthesia, use of iodine impregnated adhesive dressing, median sternotomy and/or thoracotomy incision, full heparinization (300-400 ui/kg), arterial and venous cannulation, initialization of CPB with or without aortic cross-clamping and high-potassium cold cardioplegia, surgical repair under mild-moderate hypothermia. De-clamping (if cross clamp was applied), neutralization of heparin by protamin, de-cannulation and hemostasis after surgical repair. Insertion of drain(s) and pacing wire(s). Closure of all layers in anatomical plan.

Two HD sessions will be performed at 3 days and 1 day prior to surgery. Each session will last 3 hours if the patient weighs < 75 kg, and 4 hours if > 75 kg. Conventional HD will be carried out using a volume-controlled dialysis machine. A bicarbonate dialysate containing K (3 mmol/L), Ca (1.5 mmol/L) and HCO3 (31 mmol/L) will be used. Sodium conductivity will be set at 138 mmol/L. Medium-flow filters will be used as artificial kidney devices. Dialysate temperature will be set at 36oC. Dialysate and blood flow rate will be set at 500 mL/min and 250-300 ml/min, respectively. Intradialytic ultrafiltration will not be used routinely unless the patient has volume overload. The decision to use intradialytic ultrafiltration will be taken with the anaesthesiologist and the cardiac surgeon. If intradialytic ultrafiltration is indicated, maximal rate of ultrafiltration will be 10 ml/kg/hour. These patients will undergo open heart surgery after two sessions of HD.