Dysnatremia

Question 1

Effective osmole definition and examples

Answer 1

does not diffuse freely across membrane. Na and K (due to ATPase). Not urea.

Question 2

What is the principle cause of hyponatremia

Answer 2

kidneys are unable to excrete free water

Question 3

What are the principle causes of hypernatremia?

Answer 3

sodium gain or water loss

Question 4

What is the principle regulator of water excretion and what stimulates it?

Answer 4

AVP. Increased osmolality or decreased effective circulating volume. The first is extremely sensitive, the second is not.

Question 5

What are the thresholds for thirst and ADH

Answer 5

A little bit higher threshold for thirst than ADH. Adh first then thirst

Question 6

Definition of hyponatremia/hypernatremia

Answer 6

serum sodium 145

Question 7

Cause of hyponatremia with normal plasma osmolality? Why?

Answer 7

hyperproteinemia, hyperlipidemia. Artifactual rise due to increased plasma vol w/o increase in water plasma. Use ion-selective electrode. Also, trans-urethral tumor resection

Question 8

causes of hyponatremia with high osmolality

Answer 8

hyperglycemia, mannitol infusion

Question 9

Causes of hypovolemic hyponatremia? What will the urine osmolality be? Urine Na? Exceptions? FENa?

Answer 9

sweating, vomiting, diarrhea, diuretics. Then thirst/adh. High. Low except w/ recent diuretics, vomiting (H loss>NaHCO3 loss). Low FENa

Question 10

FENa

Answer 10

Fraction of excreted Na. 1% otherwise

Question 11

hypervolemic hyponatremia: what is it? causes?

Answer 11

total body fluid volume ^, effective circulating volume decreased. CHF, cirrhosis

Question 12

Euvolemic hyponatremia: causes

Answer 12

Syndrome of inappropriate ADH secretion (almost any brain or lung disorder). hypothyroidism, adrenal insufficiency, polydipsia

Question 13

Signs of polydipsia

Answer 13

max urine production (10-15L/d), urine osmolarity <100 mosm/L

Question 14

Symptoms of hyponatremia and their causes

Answer 14

H2O moves across BBB into brain cells. Headache, nausea, vomiting,

Question 15

How much can plasma [Na] be changed in 24 hrs? why?

Answer 15

10mmol. Osmotic demyelination syndrome or central pontine myelinolysis. Esp if hyponatremia is chronic

Question 16

Tx for acute or sever hyponatremia (plasma Na<100)

Answer 16

3% saline

Question 17

Which diuretics can cause volume depletion? Hyponatremia?

Answer 17

loop and thiazide. Thiazide (Na loss> H2O loss)

Question 18

Hypernatremia is always a state of ____

Answer 18

hyperosmolality

Question 19

Causes of hypernatremia

Answer 19

Decreased H2O intake (handicapped, not drinking), increased H2O loss (Renal:diuretics,Diabetes insipidus), Na gain (hypertonic saline administration)

Question 20

Central Diabetes Insipidus

Answer 20

impaired ADH secretion (trauma, tumor, genetic)

Question 21

Nephrogenic Diabetes insipidus

Answer 21

Resistance to ADH (inherited mutation, acquired from lithium, pregnancy, hypokalemia, hypercalcemia)

Question 22

Differentiation of CDI from NDI

Answer 22

water restriction followed by desmopressin. in cdi, urine osms increase by at least 50% after DDAVP.

Question 23

Tx of hypernatremia due to water loss

Answer 23

water thru GI route or D5w or HNS

Question 24

calculation of free water deficit

Answer 24

=total body H2O*[(serum Na/140)-1]