Current Opinions in nephrology and hypertension has an excellent review this month on the rationale for bicarbonate treatment to slow the progression of CKD. The original data animal data was derived from the 5/6 nephrectomy model where rats fed with an acid chow developed metabolic acidosis and had relatively rapid GFR decline that could be ameliorated by giving the rats sodium bicarbonate. Interestingly, switching them to a low-acid, soy-based diet had a similar effect suggesting that simply reducing net acid intake is just as effective. The same group developed a 2/3 nephrectomy model in rats where they did not develop acidosis but the decline in renal function could still be slowed by treatment with bicarbonate. Current guidelines in humans suggest that patients should be prescribed bicarbonate when the TCO2 is less than 22 but recent studies have suggested that even above this level, patients with a reduced GFR may have net acid retention in the kidney with a potential for consequent renal injury that could be prevented by alkali treatment. This, of course is balanced by the fact that we do not want to give large quantities of sodium to patients with CKD.
One suggestion is to look closer at the diet of patients with CKD. The biggest source of dietary acid is animal protein and reducing meat intake will reduce overall acid intake (in contrast, we all see elderly malnourished patients on dialysis with high pre-dialysis bicarbonate levels that is actually a negative prognostic sign). The DASH diet is high in fruits and vegetables and is already a first line treatment for hypertension. Because it has a high component of fruits and vegetables, it has a high alkali content and could substitute for exogenous bicarbonate treatment in some patients. The trade-off is that it is also high in potassium and this would need to be carefully monitored in patients with a low GFR. The take home for me is that this explains, at least in part, the deleterious effects of a diet high in animal protein in patients with CKD and that we can potentially treat acidosis in these patients without resorting to large quantities of oral sodium bicarbonate. See this previous post on the benefits of bicarbonate therapy in patients with mild CKD.