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Flashcards in Na Deck (23):
1

Serum values of Na

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

2

Normal plasma osmolality

285-300 mOsms
Nax2 + BUN/2.8 + Glucose/18

3

Basic principles of Na balance

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

4

Hyponatremia

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

5

Hypernatremia

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

6

ADH

produced in hypothalamus --> secretory granules released from posterior pituitary gland in response to:
- increased plasma osmolality
- non-osmotic signals from baroreceptors (hypovolemia)

7

Plasma osmolality is high

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

8

Plasma osmolality is low

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

9

Urinary Indices

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

10

Hyponatremia with normal Posm

hyperlipidemia, hyperproteinemia
- lipids and proteins take up more plasma space

11

Hyponatremia with elevated Posm

hyperglycemia, hypertonic mannitol
- water shifts out of cells to reestablish osmotic equilibrium --> Na more dilute

12

Primary Polydipsia

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

13

Hyponatremia Uosm<100

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

14

Hyponatremia Uosm>100

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

15

Hyponatremia with U[Na] <10 and volume depleted

kidney reabsorbing Na in effort to reexpand vascular space
- nausea, vomitting, diarrhea, burns, diuretics

16

Hyponatremia with U[Na] <10 and volume expanded

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

17

Hyponatremia with U[Na] >10 and volume depleted

kidney receiving wrong signals (salt wasting)
- adrenal insufficiency, diuretics

18

Hyponatremia with U[Na] >10 and volume expanded

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

19

Correction of Hyponatremia

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

20

Use of 3% NaCl

to quickly bring serum Na+ out of danger range

21

Hypernatremia

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

22

Diabetes Insipidus

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

23

Treatment of Hypernatremia

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