On Poor Agreement Between Dialysis Unit and Ambulatory Blood Pressures

To the Editor: With regard to blood pressure (BP) during dialysis and those obtained during ambulatory BP monitoring (ABPM), we read the paper from Liu and colleagues1 with interest. BP monitoring is performed, primarily, for safety purposes during dialysis. In doing so, the BP readings obtained during dialysis are more of an incidental by-product of technology and are not intended to guide BP control off dialysis. Wide limits of agreement and heterogeneity between studies limit generalizability of conclusions among these patients.2 In particular, the escalating disagreement with increasing stages of hypertension is a particular concern in the study by Liu and colleagues.1 All too often, far-reaching conclusions are made about BP control for the rest of the week based on these readings. Indeed, if anything, the casual practice of attempting to control BPs with ultrafiltration is clearly superior to changing medications based on predialysis and postdialysis BP.3 It is unfortunate that nephrologists in current North American practice are rarely present on site during outpatient renal dialysis, unlike their European or Japanese counterparts. The relative lack of “presence” of a nephrologist, along with limited reimbursement and scarcity of trained nursing staff may have contributed to the slow implementation of ABPM among dialysis patients in North America, despite its proven efficacy2, 4 and excellent acceptance of the procedure.5 One interesting but perhaps less well-studied aspect of dialysis-derived BP readings is the relative correlation of predialysis or postdialysis values, independent of each other, with results obtained by ABPM. In a smaller cohort of patients recruited from the University of Mississippi Medical Center,6 we observed that when both predialysis and postdialysis systolic BP measurements were entered as explanatory variables in a linear regression model, only the postdialysis systolic BP (P<.001) but not predialysis systolic BP (P=.276) retained a significant independent association with ABPM systolic BP. On the other hand, for diastolic BPs, both predialysis (P=.001) and postdialysis (P=.037) values maintained a statistically significant correlation with diastolic BP with ABPM. In this cohort of Chinese patients, we wonder whether the authors similarly observed an independent association between predialysis and postdialysis BP measurements with ABPM values.