Acid Base Abnormalities

Our metabolism constantly produces acids that are normally excreted by the kidney. Patients on dialysis lack kidney function. This can lead to accumulation of protein breakdown products contributing to chronic metabolic acidosis(1). Metabolic acidosis is mostly seen among under-dialyzed patients or those with severe liver insufficiency, uncontrolled diabetes, or lactic acidosis from various causes. The dialysis procedure allows for a transfer of buffers from the dialysate to counteract acidosis, safely bringing the acid-base status back into homeostasis(2). The National Kidney Foundation KDOQI guidelines focused on the correction of acidosis and recommended that the total levels of CO2 should be monitored and maintained above 22 mmol/L in patients with chronic kidney disease stages 3-5(3). Oral bicarbonate or bicarbonate-based fluids have been used to correct metabolic acidosis in affected patients(3,4).

Metabolic alkalosis can occur among peritoneal and hemodialysis patients. It is usually due to excessive alkali consumption or extreme volume contraction. Normal serum bicarbonate values for the general population are within the range of 20 to 29 mEq/L(5). Therapy consists of correcting the primary cause, such as discontinuation of alkaline substances or volume expansion with intravenous saline(6).

Acidosis and alkalosis are both associated with adverse patient outcomes in dialysis patients(7,8). An association between pre-dialysis bicarbonate levels and risk has been shown to follow a U-shaped curve. This association occured at a pre-dialysis bicarbonate of less than 19 mEq/L and greater than 27 mEq/L(8), but may vary for each patient depending on the underlying clinical conditions. There was also an increased hospitalization risk observed at pre-dialysis bicarbonate <20 mEq/L and >24 mEq/L. Independent from pre-dialysis bicarbonate values, high total dialysate buffer concentrations may also have a potential negative impact due to the possible development of increased post-dialysis alkalosis(9,10). Several studies have shown an association of high bicarbonate dialysate and mortality(8–11). Another DOPPS study reported that compared to patients with dialysate bicarbonate concentrations of 33-37 mEq/L, HRs were 1.07 (95% CI, 0.97-1.19) for patients with dialysate bicarbonate levels ≥ 38 mEq/L and 0.90 (95% CI, 0.80-1.01) for patients with dialysate bicarbonate ≤ 32 mEq/L(12). The authors observed that the apparent effect of bicarbonate on mortality only becomes significant after adjustment for various patient data obtained from medical records (age, sex, body mass index, and comorbid conditions).

Higher risk of hospitalization and mortality are observed on both extremes with acidosis and alkalosis Therefore, maintenance of the acid-base balance is an important part of the dialysis prescription.

References

  1. Mitch WE, Jurkovitz C, England BK. Mechanisms that cause protein and amino acid catabolism in uremia. Am J Kidney Dis. 1993;21(1):91-95. Available from: http://www.ncbi.nlm.nih.gov/pubmed/8418635.
  2. Williams AJ, Dittmer ID, McArley A, Clarke J. High bicarbonate dialysate in haemodialysis patients: effects on acidosis and nutritional status. Nephrol Dial Transplant. 1997;12(12):2633-2637. Available from: http://www.ncbi.nlm.nih.gov/pubmed/9430864.
  3. National Kidney Foundation. KDOQI Clinical Practice Guideline for Nutrition in Chronic Renal Failre. Am J Kidney Dis. 2000;35(Suppl 2):S11-S16. Available from: https://www.kidney.org/professionals/guidelines/guidelines_commentaries.
  4. Szeto C-C, Chow K-M. Metabolic acidosis and malnutrition in dialysis patients. Semin Dial. 2004;17(5):371-375. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15461746.
  5. Gennari FJ, Rimmer JM. Acid-Base Disorders in End-Stage Renal Disease: Part II. Semin Dial. 2007;3(3):161-165. Available from: http://doi.wiley.com/10.1111/j.1525-139X.1990.tb00034.x.
  6. Oh MS, Uribarri J, Weinstein J, Schreiber M, Kamel KS, Kraut JA, Madias NE, Laski ME. What unique acid-base considerations exist in dialysis patients? Semin Dial. 2004;17(5):351-364. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15461741.
  7. Seifter J. Acid-Base Disorders. (Goldman L, Schafer A, eds.). Philadelphia: Elsevier Saunders; 2016.
  8. Bommer J, Locatelli F, Satayathum S, Keen ML, Goodkin DA, Saito A, Akiba T, Port FK, Young EW. Association of predialysis serum bicarbonate levels with risk of mortality and hospitalization in the Dialysis Outcomes and Practice Patterns Study (DOPPS). Am J Kidney Dis. 2004;44(4):661-671. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15384017.
  9. John Gennari F. Very low and high predialysis serum bicarbonate levels are risk factors for mortality: what are the Appropriate Interventions? Semin Dial. 2010;23(3):253-257. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20636916.
  10. Wu DY, Shinaberger CS, Regidor DL, McAllister CJ, Kopple JD, Kalantar-Zadeh K. Association between serum bicarbonate and death in hemodialysis patients: is it better to be acidotic or alkalotic? Clin J Am Soc Nephrol. 2006;1(1):70-78. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17699193.
  11. Lowrie EG, Lew NL. Death risk in hemodialysis patients: the predictive value of commonly measured variables and an evaluation of death rate differences between facilities. Am J Kidney Dis. 1990;15(5):458-482. Available from: http://www.ncbi.nlm.nih.gov/pubmed/2333868.
  12. Tentori F, Karaboyas A, Robinson BM, Morgenstern H, Zhang J, Sen A, Ikizler TA, Rayner H, Fissell RB, Vanholder R, et al. Association of dialysate bicarbonate concentration with mortality in the Dialysis Outcomes and Practice Patterns Study (DOPPS). Am J Kidney Dis. 2013;62(4):738-746. Available from: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3832240&tool=p….

P/N 102497-01 Rev. A 06/2016