Changes in extracellular water with hemodialysis and fall in systolic blood pressure.

INTRODUCTION: Intra-dialytic hypotension (IDH) remains the most common complication with outpatient hemodialysis (HD) sessions. As fluid is removed during HD, there is contraction of the extracellular volume (ECW). We wished to determine whether the fall in ECW was associated with a fall in systolic blood pressure (SBP).

METHODS: We retrospectively reviewed the records of adult dialysis outpatients attending for their midweek sessions who had corresponding pre- and post-HD bioimpedance measurements of ECW.

RESULT: We reviewed 736 patients, median age 67 (54-76) years, 62.8% male, 45.7% diabetic with a median dialysis vintage of 24.4 (9.2-56.8) months. The percentage fall in ECW (ECW%) was associated with post-dialysis systolic blood pressure (SBP) ( r  = -0.14, p  < 0.001). Patients with SBP falls of >20 mmHg had a greater fall in ECW% compared to patients with stable SBP 7.6 (4.6-10.1) vs 6.0 (4.0-8.5), p  < 0.001). Patients with greater dialyzer urea clearance had greater fall in ECW% ( r  = 0.19, p  < 0.001). In a logistic model an increased fall in ECW% was associated with weight loss (odds ratio (OR) 1.88, 95% confidence limits (CL) 1.62-2.176, p  < 0.001), and session duration (OR 1.45 (CL 1.05-1.99), p  = 0.024), and negatively with hemodiafiltration compared to hemodialysis (OR 0.37 (0.19-0.74) p  = 0.005 and dialysate sodium to plasma gradient (OR 0.95 (CL 0.90-0.99), p  = 0.021).

CONCLUSION: We observed an association between the reduction in ECW and SBP with dialysis. Our results would advocate monitoring ECW changes during dialysis and developing biofeedback devices to control ultrafiltration and dialysate sodium to reduce the risk of IDH.