A comparative effectiveness research study of the change in blood pressure during hemodialysis treatment and survival

Abstract

It is not clear to what extent changes in blood pressure (BP) during hemodialysis affect or predict survival. Studying comparative outcomes of BP changes during hemodialysis can have major clinical implications including the impact on management strategies in hemodialysis patients. Here we undertook a retrospective cohort study of 113,255 hemodialysis patients over a 5-year period to evaluate an association between change in BP during hemodialysis and mortality. The change in BP was defined as post-hemodialysis minus pre-hemodialysis BP, and mean of BP change values during the hemodialysis session was used as a mortality predictor. The patients' average age was 61 years old and consisted of 45% women, 32% African-Americans and 58% diabetics. Over a median follow-up of 2.2 years, a total of 53,461 (47.2%) all-cause and 21,548 (25.7%) cardiovascular deaths occurred. In a fully adjusted Cox regression model with restricted cubic splines, there was a U-shaped association between change in systolic BP and all-cause mortality. Post-dialytic drops in systolic BP between -30 and 0 mm Hg were associated with greater survival, but large decreases of systolic BP (more than -30 mm Hg) and any increase in systolic BP (over 0 mm Hg) were related to increased mortality. Peak survival was found at a change in systolic BP of -14 mm Hg. The U-shaped association was also found for cardiovascular mortality. Thus, modest declines in BP after hemodialysis are associated with the greatest survival, whereas any rise or large decline in BP is associated with worsened survival.

Figure 1

Association between changes in BP during HD and all-cause mortality in 113,255 patients: left; systolic BP, right; diastolic BP Note: The model was only adjusted for pre-HD BP value and the calendar quarter of entry. Dashed lines represent 95% confidence interval. Frequencies of observed patients are presented simultaneously. Abbreviations: pre-HD; pre-hemodialysis, post-HD; post-hemodialysis, sysBP; systolic blood pressure, diaBP; diastolic blood pressure.

Figure 2

Adjusted hazard ratios for all-cause mortality according to Δ systolic BP: left; case-mix adjusted model, right; case-mix plus malnutrition-inflammation cachexia syndrome adjusted model (n = 113,255) Note: Dashed lines represent 95% confidence interval. Abbreviations: pre-HD; pre-hemodialysis, post-HD; post-hemodialysis, sysBP; systolic blood pressure, MICS; malnutrition-inflammation cachexia syndrome.

Figure 3

Effect modification by pre-HD systolic BP level on the association between Δ systolic BP and all-cause mortality: A) pre-HD systolic BP <120 mmHg, B) 120 – <140 mmHg, C) 140 – <160 mmHg, D) ≥160 mmHg Note: Numbers of patients were 9,053, 26,709, 42,617 and 34,876, respectively. Models were adjusted for case-mix plus malnutrition-inflammation cachexia syndrome covariates. Dashed lines represent 95% confidence interval. Abbreviations: pre-HD; pre-hemodialysis, post-HD; post-hemodialysis, sysBP; systolic blood pressure.

Figure 4

Effect of ultrafiltration percentage and time-on-HD session on the association between Δ systolic BP and all-cause mortality: left; the model stratified by ultrafiltration percentage, right; the model stratified by time-on-HD session. Note: Ultrafiltration percentage was calculated as (ultrafiltration [kg] / post-HD body weight [kg])*100, then divided into 4 categories: <2% (n = 16,330), 2 – <3% (n = 26,740), 3 – <4% (n = 34,459), and ≥4% (n = 35,726). Time-on-HD session values were divided into 4 categories: <180 min (n = 11,732), 180 – <210 min (n = 32,396), 210 – <240 min (n = 35,135) and ≥240 min (n = 20,422). The models were fully adjusted, and hazard ratios are plotted without 95% confidence interval. Abbreviations: pre-HD; pre-hemodialysis, post-HD; post-hemodialysis, sysBP; systolic blood pressure.