Plasma volume, albumin, and fluid status in peritoneal dialysis patients

Abstract

Background and objectives: Peritoneal dialysis (PD) patients may be overhydrated especially when inflammation is present. We hypothesized that patients with a plasma albumin below the median value would have measurable overhydration without a proportional increase in plasma volume (PV).

Design, setting, participants, & measurements: We investigated a cross-sectional sample of 46 prevalent PD patients powered to detect a proportional increase in PV associated with whole body overhydration and hypoalbuminemia. PV was determined from (125)I-labeled albumin dilution, absolute total body water from D dilution (TBW(D)), and relative hydration from multifrequency bioimpedance analysis (BIA; Xitron 4200) expressed as the extracellular water (ECW):TBW(BIA) ratio.

Results: Whereas patients with plasma albumin below the median (31.4 g/dl) were overhydrated as determined both by BIA alone (ECW:TBW(BIA) 0.49 versus 0.47, P < 0.036) and the difference between estimated TBW(BIA) and measured TBW(D) (3.55 versus 0.94 L, P = 0.012), corrected PV was not different (1463 versus 1482 ml/m(2), NS). Mean PV was not different from predicted, and its variance did not correlate with any other clinical measures. Multivariate analysis showed that the only independent predictor of whole body overhydration was reduced plasma albumin.

Conclusions: Hypoalbuminemia is an important determinant of tissue overhydration in PD patients. This overhydration is not associated with an increased plasma volume. Attempts to normalize the ECW:TBW ratio in hypoalbuminemic, inflamed PD patients may lead to hypovolemia and loss of residual renal function.

Figure 1.

The relationship between TBW normalized to body weight determined from BIA (■) and D dilution (□) and the proportion of body fat determined from BIA. The near perfect correlation for the BIA data are due to the assumption that tissue hydration is the same in all patients, whereas the measured TBW indicates the variability in hydration state with the majority of patients showing evidence of overhydration.

Figure 2.

These two different estimates of overhydration are correlated, (r = 0.48, P = 0.002). The y-axis is a measure of how abnormal the ECW:TBW ratio is, being the difference between the measured value and that predicted from normal subjects, (20), whereas the x-axis is the difference between the estimated and measured TBW (BIA and D dilution, respectively).

Figure 3.

Relationship between measured and predicted PV (in ml). Most patients fall within the predicted normal limits as shown by the broken lines and are equally spread about the line of identity (solid line).

Figure 4.

Relationship between excess fluid, as determined by the difference between measured and estimated body water, and plasma albumin (R = −0.40, P = 0.011). A similar amount of variance (12% to 25%) was observed, whichever estimate of fluid status was used: ECW:TBW_BIA R = −0.49, P = 0.001; difference in ECW:TBW ratio from normal, (20) R = −0.45, P = 0.002; difference in ECW/Wt from normal, (21) R = −0.35, P = 0.018.