Kinetic analysis was performed in all 58 patients undergoing standard
CAPD. The urea distribution volume was estimated from anthropomorphic
measurements (Watson formulae). Normalized protein catabolic rate (NPC
R), daily protein leak (PL), urea and creatinine Kt/Vs, clearances and
peritoneal mass transfer coefficients (Kp) were calculated from measu
rements on serum, 24-h urine and PD fluid effluent. The mean total (re
nal + PD) daily creatinine and urea Kt/Vs (KT/V) were 0.31 (range 0.15
-0.79) and 0.31 (0.18-0.65). There was no relationship between KT/V an
d serum urea or Kp. The strongest determinant of the urea KT/V was the
residual renal urea clearance (KrU)(R = 0.79, P<0.001) which decrease
d with time on dialysis (R = -0.38, P<0.005). There was a significant
correlation between the hospital admissions per year and both the urea
and creatinine KT/V and KrU (R = -0.30, -0.32, P < 0.05). Patients wi
th urea KT/V<0.25 (n = 2) had more hospital admissions/year than those
with KT/V > 0.25 (mean of 2.6 versus 1.5, P<0.05). NPCR correlated wi
th urea KT/V(R = 0.62, P<0.001) but not with serum albumin or the PL.
Patients identified by UKM to be less well dialysed have a lower resid
ual renal function and are more likely to be hospitalized. Undernutrit
ion in CAPD patients appears to be related to underdialysis rather tha
n protein loss.