Ultrafiltration hemodynamics in conscious, uremic dogs: effect of a decreasing plasma urea level

The hemodynamic effects of a decreasing plasma urea level during hemodialysis were studied in acutely uremic, conscious dogs. Each dog was studied twice, during dialytic ultrafiltration against both a urea-free (U-) and a urea-supplemented (U+) dialysate. Plasma osmolality (-13 mosm/kg/H2O +/- 10 SD, p less than 0.01) and urea levels (-43 mg/dl +/- 20, p less than 0.01) decreased when using the (U-) dialysate, but were unchanged with the (U+) dialysate. At the end-point of volume depletion (MAP less than 80 mm Hg) total peripheral resistance index [U (+): 3,376 +/- 743 dyn . s X cm-5 X m2, U(-): 3,091 +/- 537, NS)] and blood volume [U(+): 62.7 +/- 7.4 ml/kg, U(-): 63.7 +/- 7.5, NS)] were comparable whether or not the plasma urea level had been allowed to decrease. The data suggest that an acutely decreasing plasma urea level during dialysis does not impair hemodynamic response to volume depletion in the model described.