FEN: Disorders of Phosphorus Homeostasis

Question 1

What is normal serum phosphorus concentration and what units is it in?

Answer 1

2.5-4.5 mg/dL

Question 2

Define hypophosphatemia

Answer 2

Serum phosphorus less than 2.5 mg/dL

Question 3

List four principle causes of hypophosphatemia

Answer 3

1. Increased renal elimination
2. Rapidly refeeding patients with chronic malnutrition
3. Respiratory alkalosis
4. Treatment of diabtetic ketoacidosis

Question 4

List three causes of increased renal elimination which predispose to hypophosphatemia

Answer 4

1. Diuretics
2. glucocorticoids
3. sodium bicarbonate

Question 5

Describe how treatment of diabetic ketoacidosis can lead to hypophosphatemia

Answer 5

Phosphorus shifts into the IC compartment as diabetic ketoacidosis is corrected

Question 6

List four principle signs and symptoms of hypophosphatemia

Answer 6

1. Tissue hypoxia
2. Neurologic manifestations
3. Pulmonary and cardiac symptoms
4. Other organ systems

Question 7

Describe how tissue hypoxia can occur due to hypophosphatemia

Answer 7

Tissue hypoxia can occur because of a decrease in oxygen release to peripheral tissues

Question 8

List four neurologic manifestations of hypophosphatemia

Answer 8

1. Confusion
2. Delirium
3. Seizures
4. Coma

Question 9

List four cardiopulmonary symptoms of hypophosphatemia

Answer 9

1. respiratory failure
2. Difficulty weaning from mechanic ventilation
3. Heart failure
4. Arrhythmias

Question 10

List four additional organ systems affected by hypophosphatemia

Answer 10

1. Muscle
2. Hematologic
3. Bone
4. Kidney

Question 11

List three patients at high risk for hypophosphatemia which are candidates for IV phosphorus supplementation

Answer 11

1. Malnourishment
2. Alcoholism
3. Diabetic ketoacidosis

Question 12

Describe how to supplement

IV phosphorus in patients at high risk for hypophosphatemia

Answer 12

Supplementing intravenous fluids with 10-30 mmol/L intravenous phosphorus

Question 13

What is a limitation of oral phosphorus products?

Answer 13

They can be used for asymptomatic patients but they are poorly absorbed

Question 14

What are two IV phosphate products and describe their mEq content for every 3 mmol of phosphate

Answer 14

1. sodium phosphate (4 Na+ mEq per 3 mmol of phosphate)

2. potassium phosphate (4.4 K+ mEq per 3 mmol of phosphate)

Question 15

What is a typical IV phosphate dose in symptomatic patients?

Answer 15

15-30 mmol phosphorus

Question 16

What is the maximum phosphate dose in symptomatic patients?

Answer 16

60 mmol (0.5-0.75 mmol/kg of IBW)

Question 17

What is maximum rate for infusion of IV phosphate?

Answer 17

7.5 mmol/hour

Question 18

What is typical infusion time for IV phosphate products?

Answer 18

3-6 hours

Question 19

Due to IV phosphate shortages, they should be reserved for what 5 patient groups?

Answer 19

1. children
2. neonates
3. diabetic ketoacidosis
4. refeeding syndrome
5. critically ill patients

Question 20

What macronutrient can contribute to phosphorus supplementation? And how many mmol of phos does it contribute?

Answer 20

Intravenous fat emulsions contain 15 mmol/L as egg phospholipids, this may be sufficient phosphate for some patients

Question 21

Define hyperphosphatemia

Answer 21

serum phosphorus greater than 4.5 mg/dL

Question 22

What two chronic disease contribute to hyperphosphatemia?

Answer 22

1. chronic kidney disease

2. hypoparathyroidism

Question 23

List four signs and symptoms of hyperphosphatemia

Answer 23

1. hypocalcemia
2. ECG changes
3. paresthesias
4. vascular calcifications

Question 24

Treatment of hyperphosphatemia is routine part of management of what chronic condition?

Answer 24

Chronic Kidney Disease