Hyponatremia

Question 1

Sosm equation and normal values

Answer 1

Sosm = 2 * (Na + BUN/2.8 + Gluc/18)

norm: 280-290 mOsm/kg

Question 2

What happens when Sosm increases? How does it normalize?

Answer 2

1. SOsm ↑ (>295)
2. kidney reabsorbes Na+ and H2O
3. Makes [ ] urine and ↑ SG
4. SOsm is normalized

Question 3

What happens when Sosm decreases? How does it normalize?

Answer 3

1. SOsm ↓
2. kidney excretes water
3. dilutes urine
4. lowers SG

Question 4

Main Channels of ascending loop? Distal conv. tubule?

Answer 4

AL: Na K 2Cl
DCT: thiazide sensitive NaCl

Question 5

Normal GFR

Answer 5

115-125 L/d

Question 6

ADH response is normally ____________, but during stress becomes ______

Answer 6

osmoregulatory

Volume regulatory hormone

Question 7

Most common electrolyte disturbance in hospitalized patients? What is this disorder a result of?

Answer 7

Hyponatremia - result of inability to maximally dilute the urine, coupled with water intake.

Question 8

3 categories of hyponatremia and their Sosm values

Answer 8

1. hypertonic >300 mOsm/kg
2. isotonic ~280-300 mOsm/kg
3. hypotonic

Question 9

1 reason of hypertonic hyponatremia

Answer 9

hyperglycemia → ↑ Sosm

*note: hyponatremia are due to shift of water from cells in response to non-Na+ solutes

Question 10

Common reasons for isotonic hyponatremia

Answer 10

hyperlipidemia

hyperproteinemia

Question 11

Common reasons for hypotonic hyponatremia

Answer 11

increased ADH release → reabsorb H2O → cant dilute urine

note: increase in ADH relies on volume status

Question 12

3 types of hypotonic hypernatremia

Answer 12

Hypotonic Hyponatremia:

1. Hypovolemic
2. Euvolemic
3. Hypervolemic

Question 13

↑ Serum uric acid suggests what?

Answer 13

volume depletion

Question 14

↓ Serum uric acid suggests what?

Answer 14

euvolemia

Question 15

Hypovolemia (Hypotonic Hyponatremia) indicates what?

Answer 15

Low total body sodium (clinically low ECF volume)

Question 16

Euvolemia (Hypotonic Hyponatremia) indicates what?

Answer 16

Normal total body sodium (clinically normal ECF volume)

Question 17

Which Hypotonic Hyponatremia is ADH secretion inappropriate?:

1. Hypovolemic
2. Euvolemic
3. Hypervolemic

Answer 17

Euvolemia:
ADH is secreted despite absence of:
1. increase Posm
2. decreased effective vascular volume

Question 18

Hypovolemic (Hypotonic) Hyponatremia is caused by what ddx?

Answer 18

SMDOG

1. gastrointestinal losses
2. Diuretic overuse or abuse
3. Osmotic diuresis
4. Salt losing nephrITIS
5. mineralocorticoid deficiency

Question 19

How does mineralocorticoid deficiency lead to hypovolemia?

Answer 19

ADH secretion is increased the more Mineralocorticoids are deficient→ reabsorbs more H2O → low TB sodium → Low ECF vol

Question 20

Causes of hypervolemic (Hypotonic) Hyponatremia

Answer 20

1. CHF
2. Hepatic cirrhosis
3. nephROTIC syndrome
   ___________________
4. ARF or CKD

*note: ARF + CKD UNa > 20

Question 21

Causes of Euvolemic (Hypotonic) Hyponatremia

Answer 21

1. SIADH
2. Primary polydipsia (drink too much water)
3. adrenal insufficiency
4. hypothyroidism
5. Drugs pharmacological agents

Question 22

Tx for hyponatremia

Answer 22

dietary water restriction + correct underlying disorder

sometimes:
hypertonic NaCl (3%) may be given w/ w/o furosemide