Parenteral Nutrients and Formulations
Therefore, when considering acid–base balance, more chloride may be used to help manage metabolic alkalosis, whereas more acetate may be used to help manage metabolic acidosis. Monitoring serum chloride and bicarbonate levels will help guide the use of these salts in PN solutions. The clinician should consider a patient’s GI losses, pulmonary function, and renal function when anticipating and managing acid–base imbalances.
Phosphate
Phosphate is often a key component of PN solutions, particularly for patients who are malnourished and at risk for refeeding syndrome. (Refer to Chapter 4 for more information on refeeding syndrome.) Phosphate may be provided as either a sodium or potassium salt: 1 mmol of sodium phosphate contains 1.33 mEq of sodium, whereas 1 mmol of potassium phosphate contains 1.5 mEq of potassium. Guidelines for phosphate pro- vision vary and include recommendations based on energy needs and weight as well as daily recommendations.22
Close monitoring of serum
levels and consideration of the patient’s clinical condition (including nutritional status and renal function) are necessary. Refer to the Appen- dix for monitoring and repletion strategies. Phosphate must not be provided in excess amounts with calcium, due
to the risk of precipitation within the PN solution. Solubility curves exist to guide clinicians on the appropriate maximum amount of calcium and phosphate that can be provided while considering other additives.23
For
adult patients, the limit is typically 28 to 30 per liter of combined calcium (mEq) and phosphate (mmol), although solubility may be affected by pH, AA product and concentration, form of calcium used, and temperature. Clinicians are encouraged to review their institution’s products and solu- bility curves with their pharmacy department to ensure an accurate limit is identified.
Magnesium
Magnesium is provided in PN solutions as magnesium sulfate. (In PN, 8.12 mEq of magnesium sulfate is equivalent to 1 g of magnesium sul- fate.) Magnesium is provided to maintain serum levels. Maintaining high-normal serum magnesium levels helps reduce ventricular ectopy and improves potassium retention.19
Higher amounts of magnesium may
be beneficial for patients with GI losses, cardiac arrhythmias, and ileus, whereas lower amounts of magnesium may be needed for those with renal impairment or for those receiving other sources of magnesium. Refer to the Appendix for monitoring and repletion strategies. For 3-in-1 PN solutions,
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