Chapter 7: Phosphorus

Question 1

List the detrimental effects of hypophosphatemia

Answer 1

1. Decreased erythrocyte ATP levels and increased RBC fragility (hemolysis)
2. Decreased 2,3-BPG, which impairs oxygen delivery to tissues (shifts dissociation curve to the left)
3. Impaired chemotaxis, phagocytosis, and bacterial killing of leukocytes
4. Shortened platelet survival times
5. Impaired clot retraction
6. Thrombocytopenia
7. Megakaryocytosis in bone marrow
8. Muscle weakness
9. Intestinal ileus (and vomiting, nausea, anorexia)
10. Impaired CNS glucose use and ATP production (can lead to encephalopathy)
11. Impaired cardiac contractility
12. Increased renal tubular bicarb wasting
13. Impaired renal ammoniagenesis
14. Bone demineralization

Question 2

Why are diabetics more at risk for hypophosphatemia?

Answer 2

Total body deficits of phosphorus due to loss of muscle mass, urinary losses, and impaired cellular uptake due to insulin deficiency

Question 3

How does hypovitaminosis D cause systemic phosphorus deficit?

Answer 3

Decreased calcium absorption stimulates PTH, which causes decreased renal phosphorus reabsorption (increased renal phosphorus excretion)

Question 4

Is hypophosphatemia a negative or positive prognostic indicator in acute liver injury/failure?

Answer 4

Positive. It is thought hypophosphatemia may represent healing and regeneration of the liver (mechanism unknown).

Question 5

What are potential side effects of excessive IV phosphorus administration?

Answer 5

1. Hypocalcemia
2. Tetany
3. Soft tissue mineralization
4. Renal failure
5. Hyperphosphatemia