Sodium Disorders

Question 1

is sodium an intracellular or extracellular ion

Answer 1

major extracellular ion

Question 2

normal Na value

Answer 2

140-160 mEq/L

cats: higher end
dogs: lower end

VERY tightly regulated - variations beyond 1-2 mEq/L from patient’s normal can start to cause signs

Question 3

what is the major problem with sodium derangements (dysnatremia)

Answer 3

water

dysnatremia leads to either water retention or loss

Question 4

how does Na influence water movement

Answer 4

endothelium: leaky barrier between IV and interstitium
- water + ions move freely

cell membrane: semi-permeable barrier between ICF and ECF
- only water moves freely

Question 5

water movement in hypernatremia

Answer 5

high Na concentration in ECF –> water moves from ICF to ECF –> cell shrinks

Question 6

water movement in hyponatremia

Answer 6

low Na concentration in ECF –> water moves from ECF to ICF –> cell swells

Question 7

should sodium derangement therapies be administered quickly or slowly

Answer 7

slowly - cell has internal mechanisms to accommodate dysnatremias

want to use treatments slowly to minimize adverse effects

Question 8

osmotic pressure

Answer 8

pressure generated by the NUMBER of molecules dissolved in water that drives water movement

ECF and ICF will try to maintain equilibrium - water moves along osmotic gradient to establish equal omolality in each

Question 9

plasma osmolality

Answer 9

depends on the total number of molecules dissolved in plasma

NOT affected by molecule size, weight, charge, shape, type, etc - each molecule contributes equally

Question 10

plasma osmolality equation

Answer 10

Osmo = (2 x Na) + (BUN / 2.8) + (BG / 18)

Question 11

clinical signs of hyper AND hyponatremia

Answer 11

1. disorientation
2. head pressing
3. obtundation
4. seizure
5. coma
6. death

most often an INCIDENTAL finding - have to be significantly out of range to cause signs

Question 12

causes of hypernatremia

Answer 12

1. increased water loss
2. decreased water intake
3. increased sodium intake (rare)

Question 13

causes of increased water loss

Answer 13

1. diabetes insipidus (central vs nephrogenic)
   - low or dysfunctional ADH –> unable to reabsorb water
2. RARE: excess panting, diarrhea

Question 14

causes of decreased water intake

Answer 14

• no access to water
• no access to water + concurrent water loss (PU without PD, diarrhea without drinking)

Question 15

causes of increased sodium intake

Answer 15

play dough, beef jerky, saltwater ingestion

Question 16

hypernatremia treatment

Answer 16

EMERGENCY (both for clinical and incidental lab finding)

if stable: electrolyte free fluid therapy @ 3-7 mL/kg/hr
- return to normal Na within 48 hours
- calculate water deficit and divide by 48 for hourly rate

if clinical: D5W fluids @ 7-10 mL/hr
- treat until neuro signs resolve
- once stable - treat as stable hypernatremia

Question 17

causes of hyponatremia

Answer 17

1. increased retention
2. excess intake (rare, healthy kidneys should be able to eliminate excess water)

Question 18

causes of increased water retention

Answer 18

1. excess ADH action when not indicated
2. low effective circulating volume
3. diuretics
4. addison’s

Question 19

hyponatremia treatment

Answer 19

EMERGENCY (only if clinical)

1. hypertonic saline
2. furosemide +/- mannitol