Intradialytic hypertension is a marker of volume excess

Abstract

Background: Intradialytic blood pressure (BP) profiles have been associated with all-cause mortality, but its pathophysiology remains unknown. We tested the hypothesis that intradialytic changes in BP reflect excess volume.

Methods: The dry weight reduction in hypertensive haemodialysis patients (DRIP) trial probed dry weight in 100 prevalent haemodialysis patients; 50 patients who did not have their dry weight probed served as time controls. In this post hoc analysis, intradialytic BP was recorded at each of the 30 dialysis treatments during the trial. The slope of intradialytic BP over dialysis was calculated by the log of BP regressed over time. Using a linear mixed model, we compared these slopes between control and ultrafiltration groups at baseline and over time, tested the effect of dry weight reduction on these slopes and finally tested the ability of change in intradialytic slopes to predict change in interdialytic systolic BP.

Results: At baseline, intradialytic systolic and diastolic BP dropped at a rate of ~3%/h (P < 0.0001). Over the course of the trial, compared to the control group, the slopes steepened in the ultrafiltration group for systolic but not diastolic BP. Those who lost the most post-dialysis weight from baseline to 4 weeks and baseline to 8 weeks also experienced the greatest steepening of slopes. Each percent per hour steepening of the intradialytic systolic BP slope was associated with 0.71 mmHg [95% confidence interval (CI) 0.01-1.42, P = 0. 048] reduction in interdialytic ambulatory systolic pressure.

Conclusions: Intradialytic BP changes appear to be associated with change in dry weight among haemodialysis patients. Among long-term haemodialysis patients, intradialytic hypertension may, thus, be a sign of volume overload.

Figures

Fig. 1

Mean slopes of systolic BP (and SEM) over dialysis treatments are shown. The numbers and their P-value reflect the changes from baseline in the corresponding periods. In the control group, the slopes of systolic BP did not change over the course of the trial. In the ultrafiltration group, the slopes of systolic BP change became steeper. The difference in slopes at both 4 and 8 weeks from baseline was statistically significant. When compared to the corresponding change from baseline in the control group, the change from baseline in the ultrafiltration group was 0.38, P = 0.20 at 4 weeks and 0.84, P = 0.035 at 8 weeks.

Fig. 2

Mean slopes of diastolic BP (and SEM) over dialysis treatments are shown. The numbers and their P-values reflect the changes from baseline in the corresponding periods. In the control group, slopes of diastolic BP did not change over the course of the trial. In the ultrafiltration group, the slopes of diastolic BP change became steeper. The change in slopes from baseline at neither 4 nor 8 weeks was statistically significant. When compared to the corresponding change from baseline in the control group, the change from baseline in the ultrafiltration group was 0.17 at 4 weeks and 0.53 at 8 weeks.

Fig. 3

Plotted are mean slopes of intradialytic systolic BP (%/h) and their standard errors from baseline to 4 weeks in the left panel and from baseline to 8 weeks in the right panel. The legend reflects the quartiles of post-dialysis weight change from baseline. Quartile 1 had the least weight change, and consequently, the change in slope of intradialytic BP was not significant for both baseline to 4 weeks and from baseline to 8 weeks. Quartile 4 had the greatest weight change and also had the greatest change in slope for both time periods. The relationship between the overall change in slopes and quartiles of weight change was highly significant (P

Fig. 4

Change in mean 44-h interdialytic ambulatory systolic BP from baseline to 4 weeks (circles) and baseline to 8 weeks (triangles) is plotted against the change in slopes of intradialytic systolic BP from baseline to the corresponding periods at 4 and 8 weeks. Negative change in mean interdialytic BP denotes a reduction in BP. Negative change in slope denotes a steepening of slopes. The intercept at zero change in the slope of intradialytic systolic BP was −9.17 mmHg (P