O73
The effects of oral sodium bicarbonate on extracellular water in patients with chronic renal
failure
Colin Jones 1 Louise Wells 1 Graham Woodrow 2 David A Ashford 3 Les Bluck 4
1 York Teaching Hospital 2 St James's University Hospital, Leeds 3 University of York 4
MRC/Human Nutrition Research Elsie Widdowson Laboratory at Cambridge
Introduction: CKD is characterised by a metabolic acidosis which is often treated with oral
sodium bicarbonate to ameliorate adverse effects on bone and protein metabolism, control
hyperkalaemia and delay CKD progression. However CKD is also characterised by sodium
retention, which may lead to hypertension and oedema. We report a study of the effects of
sodium bicarbonate on extracellular water in CKD patients.
Methods: A double blind randomised comparison of oral sodium bicarbonate versus placebo.
Patients with stage 3-5 CKD were randomised to either oral sodium bicarbonate 1.5 g three
times a day (54 mmol sodium/day) or placebo for 4 weeks. The following assessments were
performed at 0 and 4 weeks: body weight, blood pressure and assessment for oedema; serum
creatinine, electrolytes and venous bicarbonate; 24 hour urine for sodium excretion;
extracellular fluid volume and total body water determined by sodium bromide and deuterium
oxide (2H2O) dilution respectively; extracellular fluid volume and total body water by
bioimpedance. The significance of differences between the groups at week 4 was analysed by
ANCOVA, with week 0 data as the covariate.
Results: Eighteen subjects were randomised to sodium bicarbonate (group B) and 21 to
placebo (group P). Group B subjects were significantly younger (64.1 ± 2.6 yrs versus 73.4 ±
2.2 yrs, p=0.009). At week 4, serum bicarbonate was significantly higher (25.6 ± 2.4 vs 23.3
± 3.1 mmol/l, p=0.03) and blood urea lower (14.2 ± 5.6 vs 17.0 ± 5.8 mmol/l, p=0.02) in
group B. Urine sodium concentration was significantly higher in group B (82.7 ± 25.3 vs 59.0
± 21.9 mmol/l, p=0.001). Adjusting for baseline values, extracellular fluid volume (20.0 ± 4.3
vs 18.0 ± 2.9, p=0.005) and total body water (42.3 ± 9.6 vs 39.0 ± 6.8, p=0.02) as measured
by bioimpedance were significantly greater in group B at week 4. By deuterium dilution, total
body water (41.7 ± 8.3 vs 39.4 ± 6.2, p=0.01) was significantly greater in group B at week 4.
Conclusion: These results suggest that 4 weeks of oral sodium bicarbonate has a biological
effect and results in an increased body water content. However there was no evidence of a
clinical consequence (increased body weight or blood pressure). This may at least partly
reflect the fact that some of the ingested sodium load is excreted in the urine as evidenced by
an increased urine sodium concentration.