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Sodium can be provided in PN solutions in the forms of chloride, acetate, or phosphate salts. Neonates, and especially premature infants, develop a natruresis during the first 1 to 2 weeks following birth as a result of their immature kidney function. Because sodium intake is essential for protein synthesis and tissue development, adequate sodium supplementation is necessary and is guided by serum and urine sodium levels (32:Mevacor). Premature infants may require as high as 8 mEq per kg per day of sodium. Maximum sodium concentration in PN solutions should not exceed normal saline solution equivalent (154 mEq of sodium per L).

Potassium can be provided in PN solutions in the forms of chloride, acetate, or phosphate salts. Higher potassium requirements are needed during anabolism (33:Mevacor) and to correct for any gastrointestinal or renal potassium losses. Potassium concentrations in the PN solution should not exceed 80 mEq per L and potassium infusion rates in infants and children should not exceed 0.5 mEq per kg per hour (34:Mevacor). With high potassium infusion rates, the patient should be placed in the intensive care unit on a cardiac monitor because of the risk of cardiac rhythm disturbances.

The chloride-to-acetate ratio in the PN solution can be adjusted based on the patient’s acid–base status. Acetate is converted in vivo to bicarbonate at a 1:1 molar ratio. A high acetate-to-low chloride ratio can be helpful in correcting metabolic acidosis associated with hyperchloremia. Increased concentrations of acetate may also be used to help a child compensate for a respiratory acidosis. Premature infants are especially at risk for acid–base disturbances because inefficient hydrogen ion excretion and bicarbonate reabsorption by the kidneys (32:Mevacor). A low acetate-to-high chloride ratio minimizes the bicarbonate load in patients with metabolic alkalosis, such as that resulting from high gastric fluid and electrolyte losses. Caution should be used when adjusting the chloride-to-acetate ratio as dramatic acid–base changes may occur in 2 to 3 days.

Calcium and phosphate requirements in infants and children are greater than for adults due to higher demands for growth. Corticosteroids and loop diuretics, which are commonly used in neonatal and pediatric intensive care patients, can further increase calcium requirements by increasing calcium losses. Following birth, hypophosphatemia is commonly observed in premature infants due to high urinary phosphate excretion. Because phosphates dissociate in monobasic and dibasic forms, depending on solution pH, they should be dosed in millimoles (mmol) instead of mEq to avoid dosing errors. Calcium and phosphate should be provided in adequate ratio and amounts to optimize bone mineralization and prevent metabolic bone disease (35:Mevacor). Bone mineralization is optimized at an intake ratio of 2.6 mEq of calcium : 1 mmol of phosphorus (1.7 mg calcium : 1 mg phosphorus). Inadequate calcium and phosphorus supplementation often occurs because of solubility limitations of the preparations. In this circumstance, enteral calcium and phosphorus supplementation may be required. Also, cysteine hydrochloride, an acidic compound that can be added to the PN solution, can be used to lower the PN solution pH, increasing solubility and allowing higher calcium and phosphate doses in PN. An acidic medium favors the formation of monovalent phosphates instead of the divalent phosphates that would otherwise bind to calcium. Cysteine hydrochloride is added to the neonatal PN solution at a dose of 40 mg per g of amino acids.