(MHD) Lecture 10- Disorders of Sodium Concentration

Question 1

What organ synthesizes AVP (ADP) and where is the AVP stored/secreted from?

What are the main factors that cause its secretion and how much of a change in these factors is needed to cause said secretion?

Answer 1

AVP is synthesized by the hypothalamus and stored/secreted by the posterior pituitary.

• A small (1-2%) increase in osmolality or a large (10%) decrease in blood volume will increase ADH. Other factors such as drugs, pain, and stress can also lead to release.

Question 2

Name the (3) main intrarenal factors that impair water excretion, thus leading to a hyponatremic state.

Answer 2

1. Renal failure (thus decreasing GFR and thus filtration of solute and thus water)
2. Solute avidity (sticking) at proximal nephron
3. Diuretics which prevent solute reabsorption in water-impermeable distal nephron segments (thus blocking reabsorption of solute)

Question 3

What does low urinary Na+ vs normal urinary Na+ suggest about the etiology of hyponatremia?

Answer 3

– low UNa+ (< 10 meq/L) suggests extrarenal loss of Na+ or edematous disorder (in which kidneys are sodium avid, and thus causing edema, usually due to a decrease in effective circulatory volume);

– “normal” UNa+ (>20 meq/L) suggests renal loss of Na+ or excess ADH in the absence of renal sodium avidity, as in SIADH.

Question 4

Treatment of Hyponatremia

(Hypovolemic vs Hypervolemic vs Euvolemic [3 types])

Answer 4

Hypo: physiologic saline

Hyper: fluid restriction and diuretics

Eu: Mild: no treatment; Severe asymptomatic: water restriction; S_y_mptomatic: medical emergency (hypertonic saline +/- diuretics. Avoid rapid or overcorrection!!!

Question 5

Treatment of Hypernatremia (3)

Answer 5

Hypo: hypotonic fluids

Eu: water administration + ADH in central DI

Hyper: Can be complicated. May require both water admin and diuretics/dialysis

Question 6

What rate of correction should treatment of hypernatremia not go beyond? Why?

Answer 6

•Rate of correction should not exceed 0.5 mEq/L/hr, as too rapid a reduction in serum sodium and osmolality may result in shift of water into the brain and cerebral edema.

Question 7

Causes of Hypovolemic Hyponatremia (6)

Answer 7

1. Diuretics
2. Diarrhea (w/ rehydration)
3. Primary adrenal insufficiency (Addison’s)
4. Puking (Vomiting)
5. Salt-wasting
6. Excessive Sweating (w/ rehydration)

DD, PP, SS

Question 8

Causes of euvolemic hyponatremia

Answer 8

1. SIADH
2. Hypothyroidism
3. Psychogenic polydipsia
4. Beer drinker’s potomania

Question 9

Causes of Hypervolemic hyponatremia

Answer 9

1. CHF
2. Liver cirrhosis
3. Renal Failure

Question 10

Causes of hypovolemic hypernatremia

Answer 10

1. Diuretics (NO REHYDRATION)
2. Osmotic or post obstructive diuresis
3. Tubular Injury
4. Sweating
5. Diarrhea
6. Vomiting (w/o rehydration)

Question 11

Causes of euvolemic hypernatremia

Answer 11

1. Diabetes insipidus
2. Decreased thirst or water intake (nursing home syndrome)

Question 12

Causes of hypervolemic hypernatremia (3)

Answer 12

1. Hypertonic fluid administration
2. Mineralocorticoid excess states
3. Salt poisoning