Phosphorus

Question 1

What factors determine serum phosphate concentration?

Answer 1

Factors include intake, intestinal absorption, renal excretion, hormonally regulated bone resorption and deposition, and distribution between ECF and ICF.

Question 2

What causes an intracellular shift of phosphorus?

Answer 2

1. Glucose and insulin administration 2. Catecholamines 3. Alkalosis

Question 3

What is the normal serum phosphorus concentration?

Answer 3

2.7 to 4.5 mg/dl

Question 4

What causes a transcellular shift of phosphorus from cell to ECF?

Answer 4

Cellular destruction and acidosis.

Question 5

What is hypophosphatemia?

Answer 5

Serum phosphorus

Question 6

What are some conditions where hypophosphatemia is common?

Answer 6

1. Chronic alcoholism 2. Critical illness 3. Respiratory and metabolic alkalosis 4. Following treatment of ketoacidosis 5. Patients receiving phosphate binding medication 6. The administration of CHO load or PN is likely to cause hypophosphatemia if an inadequate amount of phosphate is provided, especially in malnourished patients at risk for developing severe hypophosphatemia and referring syndrome. NB: Severely malnourished pts such as those undergoing anticancer treatment, esp radiation to the GI tract, are at an increased risk for electrolyte abnormalities and fluid shift upon initiation of nutrition support. Electrolyte abnormalities should be corrected prior to nutrition support therapy and should be monitored closely as calories are carefully increased to meet estimated needs.

Question 7

What two factors determine treatment of hypophosphatemia?

Answer 7

1. Treatment of hypophosphatemia varies according to the degree of severity and the presence of symptoms. Asymptomatic mild hypophosphatemia may be treated with oral phosphate supplements if the GI tract is functional- Limitations include diarrhea and unreliable absorption. Pts with symptomatic, moderate and severe hypophospatemia as well as pets unable to tolerate oral phosphorus formulations should receive IV potassium or sodium phosphate to correct serum phosphorus levels

Question 8

What are the dose recommendations for treatment of hypophospatemia?

Answer 8

Note: Recommended doses are for patients with normal renal function. Patients w/ renal impairement should receive: 50% of the initial empirical dose.

Question 9

1. Define Hyperphosphatemia
2. What conditions may cause hyperphosphatemia?

Answer 9

1. Serum phosphorus concentration >4.7 mg/dl.
2. Hyperphosphatemia most often occurs in the setting of renal insufficiency. Other causes may include respiratory/metabolic acidosis (cause transcellular shift of P from ICF to ECF), endogenous release of P into the ECF from cellular destruction, such as massive trauma, cytotoxic agents (esp w/ treatment of lymphomas and leukemias that have large tumor burdens), hypercatabolism, hemolysis etc.

Question 10

1. What is the most serious complication of hyperphosphotemia?
2. How does it occour?
3. How do we treat hyperphosphatemia?

Answer 10

1. The most serious complication of hyperphosphatemia is soft tissue and vascular calcification.
2. Calcification occurs when the calcium-phosphorus products exceeds 55 mg^2/dl.
3. Conventional aluminum and calcium based phosphate binders can be used to reduce intestinal absorption of P. Recently developed aluminum and calcium free binders can also be used w/out the untoward risks of anemia and osteomalacia seen with use of aluminum -based agents.