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

BACKGROUND: Hypertension in chronic haemodialysis patients contributes significantly to morbidity and mortality. Treatment decisions are usually based on predialysis readings, which may not accurately reflect control during the interdialytic period.
METHODS: We studied 40 randomly selected subjects on haemodialysis and compared readings by different methods at set times during the dialysis session with the 48-h interdialytic ambulatory readings. Conventional sphygmomanometer, automated Dinamap and Tm 2421(A&D) ambulatory monitor were used for BP 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 ambulatory 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 (41%) demonstrated a marked difference (>20/10 mmHg) between the PreC(0) and preAm(6h) (white-coat effect) persisting in seven patients (19%) after a period of rest 10 min predialysis (preC(10)) and present even in self-recorded Dinamap readings. There was a significant negative relationship between the systolic rise and the number of months on dialysis (P<0.05). Mean ambulatory BP on interdialytic day 2 was significantly greater than on day 1 whereas the awake-sleep differences were less on day 2 than day 1, both perhaps reflecting differences in volume status. The 20 min post-dialysis measurement (PoC(20)) for systolic, diastolic, and mean, unlike predialysis (PreC(0) and preC(10)), onset (onC) and end of dialysis readings (enC) did not differ significantly from 48 h interdialytic means.
CONCLUSIONS: The best representation of interdialytic pressure was the 20-min post-dialysis reading. Walk-in predialysis pressures overestimate mean interdialytic pressures due to a high incidence of white-coat effect, which shows some habituation with time on dialysis. Ambulatory monitoring has a role in evaluating persistent poor blood pressure control in haemodialysis patients.