Sodium disorders

Question 1

What is normal serum sodium?

Answer 1

135-145 mEq/L

Question 2

How do you calculate normal serum osmolality?

Answer 2

(Na+ x 2) + (BUN/2.8) + (Glucose/18)

Question 3

What is the cause of neurological symptoms in hyponatremia?

Answer 3

extracellular hypo-osmolality causes swelling of brain cells leading to N/V, HA, AMS, seizure, coma, death

Question 4

What is the cause of neurological symptoms in hyper-natremia?

Answer 4

extracellular hyperosmolality causes dehyrdration and shrinkage of brain cells leading to fatigue, weakness, twitch, seizure, coma, death, cerebral vessel rupture

Question 5

What are the main triggers of ADH release?

Answer 5

plasma osmolality over 295 and decreased baroreceptor input/ hypovolemia

Question 6

What is the MOA of ADH?

Answer 6

binds V2 receptors in collecting tubule, to send Aqp 2 from cytoplasm to lumen to increase water re absorption and decrease serum osmolality

Question 7

What does urinary osmolality indicate about ADH and water reabsorption?

Answer 7

high UOsm (>100) ADH present and H2O reabsorption, low UOsm (<100) no ADH and no H2O reabsorption

Question 8

What does urinary sodium indicate about extra-cellular volume?

Answer 8

low UNa+ (10) kidney thinks ECV high (or acid base or unable to retain) secreting Na+

Question 9

Pseudohyponatremia with normal POsm is caused by what?

Answer 9

hyperlipidemia or hyperproteinemia

Question 10

Pseudohyponatremia with high POsm is caused by what?

Answer 10

hyperglycemia or hypertonic mannitol

Question 11

What tests should you run if you suspect hyponatremia and why?

Answer 11

1 POsm (hyperosmolar?)
2 UOsm (ADH?)
3 UNa+ (kidney ~ ECV?)
4 H&P (clinical, electrolytes, renal fn)

Question 12

What clinical signs would support hyponatremia?

Answer 12

volume losses (diarrhea, vomit, bleed, diuresis), medication, pain, surgery, edema, rales, S3, orthostatic vitals, skin tenting

Question 13

What are the three causes of hyponatremia with UOsm <100 and ADH is appropriately not produced?

Answer 13

1 primary polydipsia (too much H2O intake, psych)
2 beer potomania
3 tea and toast syndrome (low osmolar load)

Question 14

At what rate should you correct a sodium imbalance?

Answer 14

0.5 mEq/L/hr

Question 15

What happens if you correct hyponatremia too fast?

Answer 15

central pontine myelinolysis/ osmotic demyelination syndrome

Question 16

What does the body produce to compensate for gradual development of hyponatremia?

Answer 16

idiogenic osmoles

Question 17

What is SIADH?

Answer 17

syndrome of inappropriate ADH excretion= production of fixed amount of ADH with no input from osmotic or volume factors resulting in high UOsm

Question 18

What are some causes of hyponatremia with low UNa+ and low ECV with appropriate ADH production?

Answer 18

GI volume loss, burns, diuretics, cortisol deficiency, treat by giving saline

Question 19

How do you treat hyponatremia with low UNa+ and high ECV with inappropriate ADH production?

Answer 19

treat underlying CHF, cirrhosis, nephrosis

Question 20

What are some causes of hyponatrmia with high UNa+ and low ECV with inappropriate ADH production?

Answer 20

adrenal insufficiency, genetic salt wasting diseases, vomit, hypothyroidism, treat with fluid restriction

Question 21

What are some causes of hyponatremia with high UNa+ and high ECV with appropriate ADH production?

Answer 21

abnormal ADH production (oat cell carcinoma, SIADH), TB/pneumonia/asthma, CKD, reset osmostat

Question 22

How do you treat hyponatremia with increased ECV?

Answer 22

fluid restriction with high sodium high protein diet to increase osmolar load and ADH antagonists (Tolvaptan, conivaptan)

Question 23

What are the two causes of sodium retention that can lead to hypernatremia?

Answer 23

drinking salt water, infusion of hypertonic NaCl

Question 24

What are the sources of water loss that can lead to hypernatremia?

Answer 24

insensible (sweat)
renal (diabetes insipidus)
GI
loss into cells (rhabdomyolysis)
inadequate water intake (reset osmostat)

Question 25

What are the two types of diabetes insipidus and ?

Answer 25

central - don’t make ADH b/c hypothalamus/pituitary problem

nephrogenic- collecting tubule doesn’t respond to ADH b/c receptor problem/Li+/osmotic diuretic

Question 26

How can you differentiate between central and nephrogenic diabetes insipidus?

Answer 26

if you give desmopressin (ADH) and UOsm increases then it’s central diabetes insipidus

Question 27

How do you treat diabetes insipidus?

Answer 27

low Na+ diet
thiazide diuretic
carbamazepine/chlorpropamide to increased ADH effect
NSAIDs to block PG's (which block ADH)
if central then give ADH

Question 28

What fluids can you give to treat hypernatremia?

Answer 28

D5W
1/4 saline if low Na+ and low ECV
normal saline if low Na+ and low ECV with low BP