CLINICAL PHARMACOLOGY
TPN Electrolytes (multiple electrolyte additive) helps to maintain normal cellular metabolism during TPN (total parenteral nutrition). Providing electrolytes in appropriate amounts prevents deficiency symptoms which otherwise would occur in their absence.
Cations: Sodium is the principal extracellular cation; it helps maintain motor nerve depolarization, proper fluid balance and normal renal metabolism. Potassium is the principal intracellular cation; it helps transport dextrose across the cell membrane and contributes to normal renal function. Magnesium is an important cofactor for enzymatic reactions and helps to maintain normal CNS (central nervous system) activity and amino acid utilization. Calcium participates in muscle contraction, blood coagulation and helps maintain normal neuromuscular function.
Anions: Chloride is the principal extracellular anion which, along with bicarbonate, is involved in maintaining proper anion balance. Acetate is an important metabolic intermediate in the tricarboxylic acid cycle and is a bicarbonate alternate.
The distribution and excretion of sodium (Na+) and chloride (Cl−) are largely under the control of the kidney which maintains a balance between intake and output.
Approximately 80% of body calcium (Ca++) is excreted in the feces as insoluble salts; urinary excretion accounts for the remaining 20%.
Potassium (K+) is found in low concentration in the plasma and extracellular fluids (3.5 to 5.0 mEq/liter in a healthy adult). Normally about 80% to 90% of the potassium intake is excreted in the urine, the remainder in the stools and to a small extent, in the perspiration. The kidney does not conserve potassium well so that during fasting or in patients on a potassium-free diet, potassium loss from the body continues resulting in potassium depletion.
Magnesium (Mg++) is the second most plentiful intracellular cation. Normal plasma concentration ranges from 1.5 to 2.5 or 3.0 mEq per liter. Magnesium is excreted solely by the kidney at a rate proportional to the plasma concentration and glomerular filtration.
Acetate (CH3COO−) provides bicarbonate (HCO3−) by metabolic conversion in the liver. This has been shown to proceed readily even in the presence of severe liver disease.