Median intradialytic blood pressure can track changes evoked by probing dry-weight

Abstract

Background: Median BP obtained over a single dialysis treatment can diagnose hypertension among hemodialysis patients. Whether median BP is as useful to track change in BP is unknown.

Design, setting, participants, & measurements: Among patients participating in the dry-weight reduction in hypertensive hemodialysis patients (DRIP) trial, interdialytic ambulatory BP was recorded at baseline, 4 weeks, and 8 weeks. The mean interdialytic ambulatory BP was compared to the following recordings: predialysis on one dialysis treatment (Pre1), predialysis averaged over 2 weeks of dialysis treatment (Pre6), postdialysis on one dialysis treatment (Post1), postdialysis averaged over 2 weeks of dialysis treatment (Post6), and median intradialytic BP over one treatment.

Results: Pre1 was unable to detect change in ambulatory BP. Although Pre6 was able to detect change, it overestimated the ambulatory BP. On average, the magnitude of reduction in Post1 in response to probing dry-weight was nearly twice that obtained by ambulatory BP monitoring. Even Post6 overestimated the magnitude of reduction in BP at 8 weeks. Median systolic BP was responsive to probing dry-weight and neither overestimated nor underestimated the interdialytic ambulatory systolic BP at baseline or over time. However, the SD of the differences between median systolic BP and interdialytic ambulatory systolic BP varied from 16 to 20 mmHg.

Conclusions: Median intradialytic BP recordings can detect change in ambulatory BP evoked by reduction in dry-weight at the population level. Because of wide agreement limits between intradialytic and interdialytic BP, the individual prediction of ambulatory BP from median intradialytic BP can be misleading.

Trial registration: ClinicalTrials.gov NCT00067665.

Figure 1.

Bland-Altman plots showing mean differences between intradialytic median systolic BP and 44-hour interdialytic ambulatory systolic BP plotted against the means of the two BP recordings at baseline, week 4, and week 8 in the control and ultrafiltration groups. In the control group, paired measurements were available in 45, 45, and 34 patients at baseline, week 4, and week 8, respectively. In the ultrafiltration group, the corresponding pairs were available in 82, 85, and 68 patients. The mean differences were not different from zero at any time point. However, the limits of agreement were wide. The SD of the differences between BP measurements varied between 16 and 20 mmHg.