Chapter 24: Plasma Phosphate, Hypophosphatemia, and Hyperphosphatemia

Question 1

Plasma Phosphate

Answer 1

• normal range in adult plasma is 2.5 to 4.5 mg/dl
• symptomatic phosphate imbalances are less common than other electrolyte imbalances
• however, they may be fatal if left untreated

Question 2

Hypophosphatemia

Answer 2

• present when phosphate decreases below 2.5 mg/dl
• clinical manifestations often not observed until severe, until concentration of phosphate less than 1 mg/dl (severe symptomatic hypophosphatemia)

Question 3

Etiology of Hypophosphatemia

Answer 3

• Decreased phosphate intake or absorption (chronic alcoholism, chronic diarrhea, malabsorption syndromes, antacids that bind phosphate
• shift of phosphate from extracellular fluid to cells (refeeding after starvation/anorexia nervosa, total parenteral nutrition)
• Increased phosphate excretion (alcohol withdrawl, diuretic phase after extensive burns, emesis, hemodialysis

Question 4

Clinical Manifestations of Hypophosphatemia

Answer 4

• Due in part to decreased ATP within the cells
• also due to tissue hypoxia caused by decreased 2,3-biphosphoglycerate in the red blood cells which causes
• anorexia
• malaise
• hemolysis
• paresthesias
• diminished reflexes
• muscle aches, weakness
• respiratory failure
• confusion, stupor
• seizures
• coma
• impaired cardiac function

Question 5

Hyperphosphatemia

Answer 5

• increased in phosphate concentration above the upper limit of normal 4.5 mg/dl

Question 6

Etiology of Hyperphosphatemia

Answer 6

• increased phosphate intake or absorption (overzealous phosphate therapy, excessive use of phosphate containing enemas or laxatives)
• Shift of phosphate from cells to extracellular fluid (tumor lysis syndrome, crushing injuries, rhabdomyolysis)
• Decreased phosphate excretion (chronic kidney disease, oliguric renal kidney failure)

Question 7

Clinical Manifestations of Hyperphosphatemia

Answer 7

• Increased neuromuscular excitability which causes hypocalcemia signs and symptoms
• Excess phosphate salts may deposit in soft tissues which may lead to:
• aching and stiffness of joints
• itching
• conjunctivitis