Sodium

Question 1

Daily Na requirement

Answer 1

3 mEq/kg/day

Preemies may need 2-3X this amount (renal immaturity and rapid growth)

Question 2

Hypernatremia

Answer 2

Na > 145 mEq/L

Causes:

1. Na excess
   - mixing formula wrong
   - iatrogenic
   - sea water ingestion
   - breast milk with excess Na
   - excessive NaBicarb after resuscitation
2. water deficit
   - Diabetes Insipidus
   - diarrhea

Water following Na+ into extracellular fluid from the intracellular fluid –> pulmonary edema

Question 3

Total Body Water (TBW) = __ % of body weight?

Answer 3

60% in adolescents/adults

90% in infants

Question 4

Central Diabetes insipidus (DI)

Answer 4

Lack of ADH

Responds to exogenous vasopressin

Dilute urine, polyuria, no sugar in urine, hyperosmolar (from water deficit)

Sipping and sipping

Question 5

Nephrogenic DI

Answer 5

X-linked (males only)

Doesn’t respond to vasopressin (ADH)

Dilute urine, polyuria, no sugar in urine, hyperosmolar (from water deficit)

Sipping and sipping

Question 6

Hyponatremia

Answer 6

<130 mEq/L

<120, sz or lethargy

Due to

1. Loss of Na
   - –GI losses (urine Na <10)
   - –thiazides (increased urine Na)
2. Increased water (dilutional
   - –polydipsia (too much in)
   - –SIADH (too little out)

Question 7

The 3 types of hyponatremia

Answer 7

1. Hypovolenic
2. Euvolemic
3. Hypervolemic

Best study to figure it out is FENa

Question 8

Causes of SIADH

Answer 8

SIADH
Surgery
Infection
Axon (neuro like guillain barre, tumor)
Day after, post-op
Head injury / Hemorrhage 

Pulm or endo sometimes

Pituitary makes ADH

Chemo: vincristine, cyclophosphamide
antiepileptic: carbamazepine
Chlorpropamide (oral hypoglycemic)

Question 9

Appropriate ADH secretion

Answer 9

Hyperosmolar

Question 10

SIADH Labs

Answer 10

Hyponatremia
Elevated BP (water retention)
UOP < 1 ml/kg/day
Normal BUN and Cr (kidney still working normally)
Normal serum K
Concentrated urine Na (>25 mEq/L (25 mmol/L)
High urine osm 
Decreased BUN
Increased body weight

Question 11

Hyponatremic dehydration labs

Answer 11

Normal - elevated serum Osm
Elevated BUN
Decreased body weight

Question 12

SIADH treatment

Answer 12

Slow correction
RESTRICT FLUIDS
furosemide
Hypertonic saline (3% NaCl) if <120 mEq/L
Demeclocycline if >8 yrs old (like doxycycline)
Lithium (could be on exam, but in real life has bad side effects so not often used)

Question 13

Renal failure labs

Answer 13

Hyponatremia
—Drink fluid, but can’t pee it out

High Cr
Urine Na > 20 mEq/L

Edema
Oliguric

Question 14

Dilutional hyponatremia

Answer 14

Excess water (water intoxication)
Total body Na is NORMAL
Cerebral swelling –> seizures
Urine Na is increased

• Infants: dilute formula
• –afebrile sz, respiratory insufficiency, hypothermia, no trauma
• Kid who swims a lot (ingests H2O)
• malnutrition
• hypotonic fluids
• glucocorticoid deficiency
• hypothyroidism

Question 15

Third spacing of fluids

Hyponatremia

Answer 15

Post op

• endothelial damage
• low albumin/low oncotic pressure

Nephrotic syndrome

Urine Na <10mEq/L

Question 16

Renal salt wasting

Hyponatremia

Answer 16

Hypovolemia

Question 17

Cerebral salt wasting

Hyponatremia

Answer 17

Post op

• High UOP
• high urine Na

Tx: replace fluid and Na losses.

Question 18

Pseudohyponatremia

Answer 18

Labs show hyponatremia

Total body Na is actually elevated if edema is present (nephrotic syndrome). Excess water in tissues, Na is in there too.

Total body Na is normal is dilutional hyponatremia.