What is hypertension in chronic haemodialysis? The role of interdialytic blood pressure monitoring

Background. Hypertension in chronic haemodialysis patients contributes sign ificantly to morbidity and mortality. Treatment decisions are usually based on predialysis readings, which may not accurately reflect control during t he interdialytic period. Methods. We studied 40 randomly selected subjects on haemodialysis and comp ared readings by different methods at set times during the dialysis session with the 48-h interdialytic ambulatory readings. Conventional sphypmomanom eter, automated Dinamap and Tm 2421(A&D) ambulatory monitor were used for B P measurements. Results. Conventional sphygmomanometry and self measured automatic readings (Dinamap) were highly correlated (systolic r=0.93, P<0.001; diastolic r=0. 90, P<0.001). Mean blood pressure on arrival ((PreC(0)) 158 mmHg systolic, 80 mmHg diastolic and 106 mmHg mean) significantly overestimated the mean a mbulatory reading during the 6 h prior to attendance ((preAm(6h)) systolic 147 (P<0.01), diastolic 75 (P<0.01), mean 99 (P<0.01)). Fifteen patients (4 1%) demonstrated a marked difference (>20/10 mmHg) between the PreC(0) and preAm(6h) (white-coat effect) persisting in seven patients (19%) after a pe riod of rest 10 min predialysis (preC(10)) and present even in self-recorde d Dinamap readings. There was a significant negative relationship between t he systolic rise and the number of months on dialysis (P<0.05). Mean ambula tory BP on interdialytic day 2 was significantly greater than on day 1 wher eas the awake-sleep differences were less on day 2 than day 1, both perhaps reflecting differences in volume status. The 20 min post-dialysis measurem ent (PoC20) for systolic, diastolic, and mean, unlike predialysis (PreC(0) and preC(10)), onset (onC) and end of dialysis readings (enC) did not diffe r significantly from 48 h interdialytic means. Conclusions. The best representation of interdialytic pressure was the 20-m in post-dialysis reading. Walk-in predialysis pressures overestimate mean i nterdialytic pressures due to a high incidence of white-coat effect, which shows some habituation with time on dialysis. Ambulatory monitoring has a r ole in evaluating persistent poor blood pressure control in haemodialysis p atients.