Relative plasma volume monitoring during hemodialysis AIDS the assessment of dry weight

Abstract

Among hemodialysis patients, the assessment of dry weight remains a matter of clinical judgment because tests to assess dry weight have not been validated. The objective of this study was to evaluate and validate relative plasma volume (RPV) monitoring as a marker of dry weight. We performed RPV monitoring using the Crit-Line monitor at baseline and at 8 weeks in 150 patients participating in the Dry-Weight Reduction in Hypertensive Hemodialysis Patients Trial. The intervention group of 100 patients had dry weight probed, whereas 50 patients served as time controls. RPV slopes were defined as flat when they were less than the median (1.33% per hour) at the baseline visit. Among predominantly (87%) black hemodialysis patients, we found that flat RPV slopes suggest a volume-overloaded state for the following reasons: (1) probing dry weight in these patients led to steeper slopes; (2) those with flatter slopes at baseline had greater weight loss; (3) both baseline RPV slopes and the intensity of weight loss were found to be important for subsequent change in RPV slopes; and, most importantly, (4) RPV slopes predicted the subsequent reduction in interdialytic ambulatory systolic blood pressure. Those with the flattest slopes had the greatest decline in blood pressure on probing dry weight. Both baseline RPV slopes and the change in RPV slopes were important for subsequent changes in ambulatory systolic blood pressure. We conclude that RPV slope monitoring is a valid method to assess dry weight among hypertensive hemodialysis patients.

Trial registration: ClinicalTrials.gov NCT00067665.

Figure 1

Panel A: Modeled changes in relative plasma volume (RPV) among the two groups of patients: control and ultrafiltration. The broken lines represent the control group and the solid lines ultrafiltration group. In the control group or ultrafiltration groups, RPV intercepts were similar at baseline and unchanged at final visit. The control group at baseline had an RPV slope of 1.40 %/hr. There was no change in RPV slope (1.40%/hr) at final visit. Accordingly, the two lines are superimposed on each other. The ultrafiltration group at baseline had an RPV slope of 1.53%/hr (NS from baseline control). The RPV slope significantly (p<0.001) steepened to 2.09%/hr at final visit. Panel B: Modeled RPV slopes adjusted for post-dialysis weight changes from baseline to end of study. Similar changes as unadjusted model were seen suggesting that changes in RPV slope persist even after accounting for changes in body weight.

Figure 2

Relationship between post-dialysis weight in the two groups by phases of trial and baseline RPV slopes. Weight loss was predicted by baseline RPV slopes. Regardless of the study group, patients with steep (more negative) slopes gained weight and those with flatter slopes lost weight. Consideration of RPV slopes in the model improved the estimation of weight loss over the course of the trial (p=0.005).

Figure 3

Weight loss and baseline RPV slope are both important in modulating the change from baseline (CFB) in relative plasma volume (RPV) slopes. Low wt loss represents wt loss of <0.3 kg from baseline to end of trial. Flat slopes represent slopes flatter than 1.33%/hr. A significant interaction effect was seen between baseline RPV slope and weight loss suggesting that effect of these two factors is multiplicative on subsequent change in RPV slopes. Error bars represent the standard errors of means. The row just above the X-axis represents the number of individuals in that group.

Figure 4

Magnitude of change in 44-hour interdialytic ambulatory systolic BP with ultrafiltration is dependent on the initial RPV slope and the final RPV slope. Mean changes and their 95% confidence intervals are shown. If the confidence interval crosses zero, the mean is statistically insignificant at the 5% level.