Simultaneous cardiopulmonary bypass and dialysis

An increasing number of patients are presenting for cardiac surgery with renal impairment. A simplified technique for dialysis during cardiopulmonary bypass (CPB) was designed and evaluated in the laboratory. The system has successfully been applied to patient care. A dialysis circuit consisting of a hollow fiber dializer, a roller pump for propelling dializing fluid, and blood lines was incorporated into a simulated CPB circuit primed with blood having values comparable to those found in the uremic patient: hematocrit, 14 percent; potassium, 8.8 mEq/L; colloid osmotic pressure, 8. 7 mm Hg; creatinine, 19.6 mg/dl; BUN, 109 mg/dl. Blood flow through the dializer was controlled to produce inlet pressure of 200 mm Hg, similar to the pressure found in the arterial line filter. Lactated Ringers contained in one liter bags was used as dialysate. Dialysate was aspirated through the dializer using a roller pump. Four dialyses were carried out varying the ultrafiltration pressure and the frequency with which fresh dialysate was used. Creatinine, BUN, and potassium levels returned to normal while the colloid osmotic pressure and hematocrit were elevated. More frequent changes in dializing bath resulted in more rapid dialysance and increasing ultrafiltration pressure resulted in more rapid hematocrit and colloid osmotic pressure elevation. This technique has been applied to patients in renal failure undergoing heart surgery and has been effective in reducing fluid load and normalizing blood chemistries.