Electrolytes

Question 1

What causes Spurious Hyponatremia?

Answer 1

Blood is drawn proximal to IV infusion or central line

Question 2

When can you see Pseudohyponatremia?

Answer 2

Instruments that use “indirect” method, sample is prediluted before analysis

Question 3

How do analyzers that use the “indirect” method of calculating Soldium work?

Answer 3

Calculate the plasma/serum sodium on the assumption that the H20 content of plasma is 93%.

Question 4

When might the assumption that the H20 content of plasma is 93% be incorrect?

Answer 4

• Hypertriglyceridemia
• Hypercholesterolemia
• Hyperproteinemia

*Water content in original sample is LOWER

Question 5

How does Hyperglycemia affect Sodium?

Answer 5

• Shift in Na+ into Extracellular space

* True hyponatremia, but unrelated to any intrinsic defect in sodium homeostasis

Question 6

Formula used to assess the degree of change in sodium concentration attributable to glucose

Answer 6

1.6 X (serum glucose - 100) / 100

Question 7

What does Hypertonic (>295 mOsm/kg) Hyponatremia suggest?

Answer 7

• Hyperglycemia (marked)

- Mannitol (reduce ICP)

Question 8

Hypotonic Hyponatremia (<280 mOsm/kg):
-Hypovolemic (Renal Loss) (5)

Answer 8

Increased Urine Sodium

• Diuretics
• Renal medullary dz
• Addison dz (primary adrenal insuff.)
• RTA type I
• Cerebral salt wasting syndrome

Question 9

Hypotonic Hyponatremia (<280 mOsm/kg):
-Hypovolemic (Extrarenal loss) (2)

Answer 9

Low Urine Sodium

• GI (V/D)
• 3rd spacing (peritonitis/pleuritis)

Question 10

Hypotonic Hyponatremia (<280 mOsm/kg):
-Euvolemic (9)

Answer 10

• SIADH
• Psychogenic polydipsia
• HypOthroidism
• Addison Dz
• ADH/Vasopressin-like drugs
• Desmopressin
• SSRis
• TCAs
• MDMA

Question 11

Hypotonic Hyponatremia (<280 mOsm/kg):
-Hypervolemic (3)

Answer 11

• CHF
• Cirrhosis
• Nephrotic syndrome

Question 12

When do you most commonly see Hypernatremia?

Answer 12

Excess water loss and inability to respond to thirst response (Infants, ICU, debilitated)

Question 13

Hypernatremia:

-Central Diabetes Insipidus

Answer 13

Damage to hypothalamus or nuerohypophysis

Question 14

Hypernatremia:

-Nephrogenic (5)

Answer 14

Diseases that affect Medullary space:
-Sickle Cell, Tubulointerstitial nephritis
Electrolyte disturbances:
-HypOKalemia and HyperCalcemia
Renal Tubular Acidosis
Fanconi Syndrome
Drugs:
-Lithium, democlocyline, colchicine, AmptoB, gentamicin, furosemide

Question 15

General causes of Hypokalemia. (3)

Answer 15

• Renal loss
• GI loss
• Transcellular shift

Question 16

Hypokalemia:

-Renal loss (10)

Answer 16

Urinary K+ >30mEq/day

• Diuretics
• Hypomagensemia
• Abx
• Minearlocorticoid excess
• RTA types I and II
• CAH
• Bartter syndrome
• Liddle syndrome
• Gitelmand syndrome
• Licorice (glyceyrrhizin)

Question 17

Hypokalemia:

-GI loss (4)

Answer 17

• Vomiting
• NG tube suction
• Diarrhea
• Villous Adenoma

Question 18

Hypokalemia:

-Transcellular shift (2)

Answer 18

• Metabolic Alkalosis

- Correction of DKA

Question 19

What happens to Potassium in DKA?

Answer 19

• Initial Hyperkalemia
• Profound Hypokalemia with correction of DKA

*Must give supplemental K+

Question 20

What happens to Potassium in Acidotic states?

Answer 20

HyperKalemia

Question 21

What are the acidotic states that are NOT associated with hyperkalemis?

Answer 21

RTA types I and II (hypokalemia)

Question 22

T/F: 50% of serum calcium is bound to protein.

Answer 22

True; primarily Albumin

Question 23

What are Calcium levels in a patient with Hypoalbuminemia?

Answer 23

• Total calcium LOW

- Free (ionized) calcium is Normal

Question 24

What happens to Calcium in acidosis?

Answer 24

• Decreases binding of calcium to Albumin

- Increases the proportion of free calcium

Question 25

What happens to free calcium in Alkalosis?

Answer 25

Decreases

Question 26

Presentation of pt. with Hypercalcemia. (4)

Answer 26

- CNS depression - N/V/Constipation - Peaked T waves on ECG - Nephrolithiasis

Question 27

Hypercalcemia increases the risk of what? (2)

Answer 27

- Pancreatitis | - Peptic ulcer disease

Question 28

What is calciphylaxis and what causes it?

Answer 28

Metastatic calcification of vessel walls and soft tissue | -Long term hypercalcemia with concomitant hyperphosphatemia (increased Ca x phosphate product)

Question 29

Primary hyperparathryoidism lab findings. (5)

Answer 29

- Increased PTH - Increased Ca++ - Decreased Phosphate - Increased Cl-/PO4- ratio - Increased urinary cAMP

Question 30

Define Secondary Hyperparathyroidism.

Answer 30

Excessive secretion of PTH in response to hypocalcemia of any cause.

Question 31

MCC of secondary hyperparathyroidism.

Answer 31

Chronic Renal Failure

Question 32

What malignancy are most commonly associated with Hypercalcemia (PTHrP)? (3)

Answer 32

- SCC (Lung, Head/Neck, Skin, Cervix, Esphagus) - Breast - T-cell Lymphoma

Question 33

T/F: Hypervitaminosis D leads to increased calcium and phosphate.

Answer 33

True

Question 34

MCC of primary hyperparathryoidism.

Answer 34

Parathyroid adenoma

Question 35

Familial hypocalciuric hypercacemia gene/chr.

Answer 35

CASR gene on chr3

Question 36

Which forms of PTH have biologic activity, what is their T1/2?

Answer 36

- Intact PTH - N-terminal PTH *T1/2 - 5 minutes

Question 37

PTH forms that do not have biologic activity and T1/2.

Answer 37

- Mid-region PTH - C-terminal PTH *T1/2 - 36 hours

Question 38

What causes CNS excitabitility (low or high Ca++)?

Answer 38

Hypocalcemia

Question 39

Hypocalcemia presentation and classic exam findings. (5)

Answer 39

- Perioral tingling (paresthesia) - Muscle spasm - Hyperreflexia - Chvostek sign (twitching of the facial muscles in response to tapping over the area of the facial nerve) - Trousseau sign (carpopedal spasm that results from ischemia)

Question 40

Hypocalcemia Cardiac manifestations. (3)

Answer 40

- QT prolongation - Low-voltage T waves - Dysrhythmias

Question 41

F/T: Primary hypoparathyroidism is most often iatrogenic.

Answer 41

True