Na

Question 1

Serum values of Na

Answer 1

Normal = 135-145 meq/L
Hyponatremia = 145 meq/L

Question 2

Normal plasma osmolality

Answer 2

285-300 mOsms

Nax2 + BUN/2.8 + Glucose/18

Question 3

Basic principles of Na balance

Answer 3

Problems almost always water problem, not Na problem
symptoms are due to alterations in plasma osmolality –> changes in brain cells
Can use kidney’s response to determine cause

Question 4

Hyponatremia

Answer 4

extracellular hypoosmolality –> water moves into cells –> cell swelling (brain)
- <115 = obtundation, seizures, coma

Question 5

Hypernatremia

Answer 5

extracellular hyperosmolality –> water moves out of cells –> cells shrink and dehydrate
Sx = lethargy, weakness, irritability, twitching, seizures, coma, death

Question 6

ADH

Answer 6

produced in hypothalamus –> secretory granules released from posterior pituitary gland in response to:

• increased plasma osmolality
• non-osmotic signals from baroreceptors (hypovolemia)

Question 7

Plasma osmolality is high

Answer 7

thirst
ADH released
collecting tubule permeability to water increases
high urine osmolality

Question 8

Plasma osmolality is low

Answer 8

no thirst
No ADH release
Collecting tubules become impermeable to water
low urine osmolality

Question 9

Urinary Indices

Answer 9

High Urine Osmolality –> ADH present and kidney resorbing water
Low Urine Osmolality –> ADH low/absent and kidney excreting water

Question 10

Hyponatremia with normal Posm

Answer 10

hyperlipidemia, hyperproteinemia

- lipids and proteins take up more plasma space

Question 11

Hyponatremia with elevated Posm

Answer 11

hyperglycemia, hypertonic mannitol

- water shifts out of cells to reestablish osmotic equilibrium –> Na more dilute

Question 12

Primary Polydipsia

Answer 12

Urine osmolality - 50 mosm/L
Daily osmolar load - 500-750
Max volume of water you can excrete:
500/50 = 10 L/day OR 750/50 = 15 L/day
Tx: fluid restrict

Question 13

Hyponatremia Uosm<100

Answer 13

ADH not being produced due to appropriate response to hypoosmolality (Primary Polydipsia)

Question 14

Hyponatremia Uosm>100

Answer 14

Most hyponatremia
- urine is concentrated –> ADH present
ADH release either “inappropriate” when plasma hypoosmotic or appropriate if volume depletion

Question 15

Hyponatremia with U[Na] <10 and volume depleted

Answer 15

kidney reabsorbing Na in effort to reexpand vascular space

- nausea, vomitting, diarrhea, burns, diuretics

Question 16

Hyponatremia with U[Na] <10 and volume expanded

Answer 16

kidney receiving wrong signals (volume expansion but ECV depletion)
- edematous states (CHF/cirrhosis)

Question 17

Hyponatremia with U[Na] >10 and volume depleted

Answer 17

kidney receiving wrong signals (salt wasting)

- adrenal insufficiency, diuretics

Question 18

Hyponatremia with U[Na] >10 and volume expanded

Answer 18

SIADH –> syndrome of inappropriate ADH secretion
- ADH secretion is fixed without regard to osmotic or volume stimuli
- Uosm is inappropriately fixed at high level
Tx= fluid restriction and increased sodium intake

Question 19

Correction of Hyponatremia

Answer 19

BE GENTLE

• slowly correct (0.5 meq/L/hr)
• if developed rapidly, can correct faster
• if chronic –> brain has adapted, need to correct slowly

Question 20

Use of 3% NaCl

Answer 20

to quickly bring serum Na+ out of danger range

Question 21

Hypernatremia

Answer 21

excessive water loss or inadequate water intake
- thirst stimulus
Causes
- sodium retention (RARE)
- water loss/inadequate intake: diabetes insipidus, diuretics, GI loss of water

Question 22

Diabetes Insipidus

Answer 22

Central = no release of ADH –> kidney cannot reabsorb water
Nephrogenic = collecting tubules don’t response to ADH –> kidney cannot reabsorb water
- LITHIUM can cause nephrogenic DI

Question 23

Treatment of Hypernatremia

Answer 23

chronic: correct SLOWLY (0.5 meq/L/hr)
- use 5% dextrose
- follow Na levels