Bone Disease and Calcium

Metabolic bone disease or osteopenia can occur with long-term (more than one year) TPN therapy. Risk factors for the development of osteopenia while on TPN include deficiencies of calcium, phosphorus, and vitamin D. Aluminum, which can be a contaminant of the formulation, above 5 micrograms per kilogram per day can decrease bone mineralization and lead to metabolic bone disease. The highest risk patient is a premature infant who is born before 34 weeks of gestational age or is less than 1.5 kg at birth. In these patients, administration of calcium and phosphorus at a 1.7:1 ratio (by weight) can reduce bone losses by around 90%.

 

For adult patients, signs and symptoms of bone disease can include a loss of height and back or bone pain.. There are several strategies to manage metabolic bone disease that include the following:

·        Assure adequate provision of minerals (15 mEq calcium, 15 mM phosphorus, and a balance of magnesium according to urine losses

·        Add adequate acetate to formula in cases of metabolic acidosis

·        Monitor calcium, phosphorus, magnesium, and acetate blood concentrations monthly or more frequently and check urinary balance of calcium and magnesium once or twice per year to adjust amounts provided in formulation to maintain balance

·        When nutritionally stable, lower the protein formulations to 1 mg/kg/day

·        Encourage lifestyle changes that support bone mineral retention, such as physical activity and smoking cessation

·        Minimize corticosteroids or other medications with bone resorption as a potential adverse effect

·        Monitor bone density through DEXA scans yearly and consider medication treatment of bone loss

 

Low levels of calcium can exacerbate bone disease and may be caused by inadequate vitamin D consumption, hypoalbuminemia, hypomagnesemia, hypoparathyroidism, and coadministration with blood products that bind calcium. Clinical features include tetany, seizure, arrhythmias, and irritability. If low levels of calcium are not associated with albumin levels, calcium supplementation may be indicated.

 

Hypercalcemia occurs with excess vitamin D intake, certain cancers, renal failure, hyperparathyroidism, the stress response, and immobilization. Muscle weakness, nausea and vomiting, dehydration, and confusion are symptoms of high calcium levels. Additional fluids, inorganic phosphate, and bisphosphonates can be used to balance calcium levels.