Disorders of Calcium, Magnesium, and Phosphorous

Question 1

What are the normal serum levels of calcium, magnesium, and phosphorous?

Answer 1

Calcium: 8.5 - 10.5 mg/dL
Magnesium: 1.4 - 1.8 mg/dL
Phosphorous: 2.5 - 4.5 mg/dL

Question 2

In response to dropping levels of Ca++, how does the body compensate?

Answer 2

Increase in PTH by the parathyroid gland which leads to:

• increased osteoclast activity
• increased reabsorption of Ca++ in kidneys
• increased reabsorption of Ca++ in intestines

Question 3

What are the major factors of accurate calcium readings?

Answer 3

pH of plasma

• low pH = loosely bound Ca++, high active Ca++ (hyper)
• high pH = highly bound Ca++, low active Ca++ (hypo)

Albumin concentration
- hypoalbuminemia (<4g/dL) = falsely low Ca++

Question 4

Whats the correction factor for Ca++ involving albumin?

Answer 4

[(Normal alb - Obs. alb) x0.8] +obs. Ca++

Question 5

What [Ca++] is considered hypocalcemia? hypercalcemia?

Causes?
S/S for each?

Answer 5

Hypocalcemia - 8.5mg/dL cause: no PTH, vit D, S/S tetany
Hypercalcemia 10.5mg/dL
Causes
-malignancies: lung and breast cancer
-hyperparathyroidism
-thiazides and lithium (increase reabsorption of Ca++ in kidneys)

S/S: Stones, moans, groans, and of course the heart

• weakness, lethargy, N/V, polyuria, polydipsia
• shortened QT interval

Question 6

What are the acute and chronic treatment for hypocalcemia?

Answer 6

ACUTE
IV calcium salts, don’t infuse faster than 60mg/min DONT GIVE WITH BICARBONATE

CHRONIC
PO calcium salts 2-4g/day with 0.25-2 mcg vitamin D3

Question 7

What are the acute and chronic treatment for hypercalcemia?

Answer 7

ACUTE (good kidneys)
IV normal saline to flush out (200-300mL/hr)
IV furosemide 40-80mg Q1-4 hrs (only give if hydrated)

ACUTE (bad kidneys)
Calcitonin 4U/kg q12hrs for 2-3 days

CHRONIC
Bisphosphonates - monitor closely for risk of hypocalcemia

Question 8

When monitoring patients after administration of drugs, which lab value(s) should you measure?

Answer 8

Ca++, Phosphorous, Magnesium

Question 9

In patients that are hypokalemic, hypomagnesemic, and hyponatremic, which electrolyte do you supply first always?

Answer 9

Magnesium because it is not effectively stored in the body

Question 10

What [Mg++] is considered hypomagnesemic? hypermagnesemic?

Causes?
S/S for each?

Answer 10

Hypo 1.4
Causes: poor nutrition, drugs: loops, amphotericin
S/S: hyperactive reflexes, arrhythmia

Hyper 1.8 mg/dL
Causes: renal failure, Mg++ containing antacids
S/S: arrhythmias, slow reflexes, weakness, paralysis

Question 11

What is the treatment for hypomagnesemia? What should you monitor?

Answer 11

PO or IV Mg++

• IV Mg++ in severe cases
• 50% of a IV Mg++ dose is eliminated in urine so monitor closely

Question 12

What is the treatment for hypermagnesemia? What should you monitor?

Answer 12

Good kidneys - flush out same as hypercalcemia

Really high Mg++ and arrhythmias - 1-2g IV CaGluconate repeated hourly

Bad kidneys - hemodialysis

Question 13

What [PO43-] is considered hypophosphatemia? hyperphosphatemia?

Causes?
S/S for each?

Answer 13

Hypo - 2.5mg/dL
Causes: poor intake, excessive Ca, Al antacid intake
S/S: muscle weakness, resp. dep., seizures (levels have to be really low)

Hyper - 4.5 mg/dL
Causes: bad renal function, hypoparathyroidism, enemas (Na3PO4)
S/S: Ca3(PO4)2 crystals, organ damage

Question 14

What is the treatment for mild-moderate and severe hypophosphotemia?

Answer 14

These meds consist of phosphorous with a cation (Na+ or K+)

Mild-moderate: serum 1-2 mg/dL (NEUTRAL, Na, K)
- PO therapy

Severe: serum <1 mg/dL (K, Na)
- IV therapy

Question 15

What is the treatment for hyperphosphotemia?

Answer 15

If symptomatic, IV calcium
If asymptomatic chronic, phosphate binders (Sevelamer)
- decreased phosphorous intake