Supplementary Material for: Increased Weight Gain During the Long Interdialytic Period Is Associated with Minor Effects on Blood Pressure Control in Clinically Stable In-Centre Haemodialysis Patients

Background/Aims: Three-day-a-week chronic haemodialysis (cHD) involves 1 long (72 h) and 2 short (48 h) inter-dialytic periods (IDPs). We aimed to determine whether BP control following the long IDP is inferior to the short IDPs. Methods: All pre- and post-dialysis BP and weight measurements over a 4-week period were retrospectively analyzed among 135 clinically stable cHD patients at 2 academic centres with comparisons between measurements recorded following short and long IDPs. Subsequently, 23 clinically stable cHD patients underwent 24-h ambulatory blood pressure monitoring (ABPM) during the final day/night cycle of the long IDP and 1 short IDP within the same week. Results: In combined and separate analyses of the 2 retrospective cohorts, pre-dialysis BP parameters were not different following long and short IDPs despite greater inter-dialytic weight gain (IDWG) during the long IDP. Subgroup analyses of the total cohort showed no evidence for inferior BP control during the long IDP among those with high %IDWG. In the ABPM study, nocturnal hypertension and loss of nocturnal dipping were frequent. Furthermore, daytime systolic blood pressure (SBP) and pulse pressure were modestly higher during the last day/night cycle of the long compared with short IDP. Conclusion: In stable cHD patients, the greater IDWG that occurred during the long IDP was not associated with overtly inferior BP control as reflected in pre-dialysis BP measurements. However, modestly higher daytime SBP was evident towards the end of the long IDP by 24 h ABPM. Thus, while fluid gain has well-documented associations with hypertension and adverse cardiovascular outcomes, the excess IDWG that occurs during the long IDP exerts relatively minor effects on BP control in patients on well-established dialysis regimens that are better identified by ambulatory monitoring.