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Use of peritoneal dialysis solution requires understanding of physiology behind process



From the September 22, 1999 issue

PROBLEM: For a few weeks, peritoneal dialysis was carried out on an anephric infant using commercially available DIANEAL (Baxter Healthcare) dialysis solutions. As needed, pharmacists would add supplementary electrolytes to the solution. However, when the infant's clinical condition changed, the physician wrote an order for a tailor-made dialysis solution, listing the amount of each electrolyte, including 140 mEq of sodium as chloride and bicarbonate. The pharmacist, being accustomed to adjusting electrolytes in dialysis solutions, wrongly assumed that the ordered electrolytes should be added to the Dianeal instead of sterile water for injection (SWFI) as the base. DIANEAL solution already contains an electrolyte composition near that of plasma, with 140 mEq/L of sodium. To prepare the ordered solution, the pharmacist mixed an additional 140 mEq/L of sodium into the DIANEAL solution, equaling a total sodium content of about 280 mEq/L. Although he knew that DIANEAL contained an inherent amount of electrolytes, he believed he was simply adding more sodium to the solution, similar to treating electrolyte deficiencies as one would by increasing the amount of sodium in total parenteral nutrition. The pharmacist had limited knowledge of the principles governing peritoneal dialysis. He didn't realize that the patient's serum sodium level would increase in order to equilibrate with the solution's concentration during each cycle of peritoneal dialysis. The dialysis nurse did not detect the error since the pharmacy label, which listed only the additives to the DIANEAL solution, was placed inadvertently over the manufacturer's label, covering the type/amount of electrolytes inherent in DIANEAL. The pharmacist also did not recognize that the bicarbonate he added to the solution would precipitate with calcium in DIANEAL. The neonate's dialysis line clogged during the night from the calcium carbonate precipitate. Later, a nurse recognized the error after reexamining the label, but by then the neonate's sodium level was over 200 mEq/L (n=135-147 mEq/L). The baby's condition deteriorated and he died a few days later.

SAFE PRACTICE RECOMMENDATION: Strategies to prevent similar errors include using recipe cards in the pharmacy and preprinted order forms for peritoneal dialysis solutions. The forms should list typical ranges of electrolytes per liter and prompt prescribers to clearly indicate the base solution (or sterile water for injection) and the total amount of electrolytes needed. Alert staff to potential incompatibility between calcium-containing solutions and sodium bicarbonate. Pharmacy labels for peritoneal dialysis solutions should clearly indicate the total mEq/L of electrolytes. They should be placed on bags in a way that avoids covering the manufacturer's label if commercially available solutions are used as a base. Additionally, require the dialysis nurse to check the solution's label against the original order and have another nurse independently recheck the solution. Equally important, practitioners who treat dialysis patients, including pharmacists who prepare or dispense dialysis solutions, should clearly understand the physiology behind the process. Dialysis is the movement of ions and small molecules, including water, across a dialyzing membrane, such as the semi-permeable peritoneal membrane. The direction of particle transfer is guided by osmosis: the movement of water across an osmotic membrane from a more dilute solution into a more concentrated solution. Glucose, the common osmotic agent in dialysis solutions, creates a greater concentration gradient across the membrane to remove excess fluid from the blood. Simultaneously, ions or other small particles may cross the membrane through diffusion: the movement of solutes from an area of greater to lesser concentration. Typically, urea, creatinine, uric acid, potassium, and phosphate move from the patient's blood (higher concentration) to the dialysate (lower concentration) with the net effect of lowering their concentration in the blood. However, using dialysate with an electrolyte concentration higher than the patient's plasma will cause the patient's serum levels to equalize with the dialysis solution during each cycle of dialysis by moving water and electrolytes through the semi-permeable membrane. This occurred in the case cited above.

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