Patient related factors leading to slow urea transfer in the body during dialysis.

We studied the trans compartmental speed of urea transfer by comparing concentration changes of blood urea nitrogen to mass changes of urea during 80 dialyses in six patients. The speed of urea transfer was studied as a dependent factor of 15 patient characteristics: age; gender; fluid overload; and pre and post values of and change in pulse and temperature, calcitonin gene related peptide, and mean arterial blood pressure. Concentration changes in blood urea nitrogen were measured as pre and post dialysis urea concentration, the total urea in the body was measured by pre dialysis urea and tritium total body water determinations, and the actual mass of urea removed by collecting all dialysate. As a mean, concentration of blood urea nitrogen fell 54% but the mass urea removed was only 40% for a mean ratio of 1.41. Nine factors were associated with the speed of urea transfer. Patients with fast transfer had more normal fluid balance, a normal pulse rate, body temperature, calcitonin gene related peptide values, and blood pressure both before and after dialysis. The patients with a slower transfer of urea had a lower blood pressure before and after dialysis and a more labile pulse rate and body temperature. Patients with unpredictable urea transfer were the most edematous and had the most labile blood pressure. It is important to know which patients have slow urea transfer. Such patients should not be treated by fast dialysis, and those with the slowest rates may do particularly well on continuous ambulatory peritoneal dialysis.(ABSTRACT TRUNCATED AT 250 WORDS)