TBW
- Men 0.6 x weight
- Women 0.5 x weight
- Elderly have less
Hyponatremia is a disorder of water regulation. Most cases of hyponatremia
are from problems in water excretions, kidney failure or CHF.
- Pseudohyponatremia: serum Na is normal but serum osmolality is normal
- Severe hypertriglyceridemia (TG’s in 1000’s)
- Severe hypoproteinemia (such as in multiple myeloma)
- Hyponatremia with hypertonicity
- Severe hyperglycemia (DKA)
- Mannitol
- Hyponatremia with hypotonicity (“true” hyponatremia): Requires continued water intake
- Renal failure
- ECFV depletion (increased resorption of water)
- Edematous states (increased resorption of water, e.g. CHF, liver failure)
- Thiazide diuretics
- SIADH
- Endocrine (hypothyroidism, adrenal insufficiency)
- Diminished solute intake: “tea and toast” diet, “beer potomania”
Workup
#1 FLUID RESTRICTION!!! to < 800 ml/24 hrs. This will buy you some time (hours).
- When faced with a low sodium value, first check a serum osmolality.
- If it’s low, you can immediately eliminate the first two above
(pseudohyponatremia and hyponatremia with hypertonicity) and concentrate on
the hyponatremia.
- If you're not sure if the pt is dehydrated (vomiting) or SIADH, give slow NS.
- If the sodium corrects, then the problem was dehydration.
- If the sodium does not correct then the problem is SIADH
- In this case, calculate the sodium deficit
- Sodium deficit = ([Na]desired – [Na]measured ) x TBW
- 1L of NS has 154 mEq of Na
- 0.9 % to 3% = 3 1/3 and 154 x 3.33 = 513 1/3 So 1L 3% saline has 513 mEq Na
CHF, nephrotic syndrome, CRH, cirrhosis, thiazide diuretics Fig 3-2 Tx Loop
diuretic causes more loss of water than Na, so give.