sodium Flashcards
how much body weight does water account for? How much is in ICF and ECF?
- 60% of body weight
- TBW = 40 L
- 2/3 is in ICF = 25 L
- 1/3 is in ECF = 15 L
is body water less or more in obese individuals
- proportion of TBW per weight is less in obese adults
- body fat is essentially free of water
of the body water that is in the extracellular fluid, how much is in interstitial fluid and plasma
- 3/4 = interstitial fluid
- 1/4 = plasma
normal range of osmolality? when so symptoms occur
280-295 mOsm/kg
- symptoms occur if
- > 320
- < 265
What is the equation to calculate osmolality
- osmolality = 2 Na + (glucose/18) + (BUN/2.8)
where does fluid tend to shift in hyponatremic conditions? Hypernatremic?
- Hyponatremic: water movement from ECF -> ICF => cell swells
- hypernatremic: water movement from ICF -> ECF => cell shrinks
isotonic changes in body fluids are largely confined to what
ECF
these clinical features are consistent with what volume status
- increased thirst, decreased sweating
- decreased skin turgor and dry mucus membranes
- olifuria with increased urine concentration
- CNS depression
- weakness and muscle cramps
- decreased BP
- tachycardia
hypovolemia
list causes of sequestration causing hypovolemia
- bowel obstruction
- peritonitis
- pancreatitis
- sepsis
these clinical features are characteristics of what volume status
- edema
- SOB
- orthopnea, PND
- HTN, tachycardia
- ? crackles
- JVD
- hepatojugular reflux
hypervolemia
what conditions can cause primary renal sodium retention
- ARF
- acute GN
- chronic RF
- nephrotic syndrome
- cushing’s syndrome
- liver disease
what conditions can cause secondary renal sodium retention
- heart failure
- liver disease
- pregnancy
where is ADH produced and stored
- produced in hypothalamus
- transported to and stored in posterior pituitary
function of aldosterone
- increase renal sodium reabsorption
- increase renal potassium secretion
homeostatic mechanisms respond to what rather than the total extracellular fluid volume
- effective circulating volume (intravascular volume)
- therefore conditions in which there is total ECF excess but decreased ECV continue to stimulate volume sensors to promote further salt and water retention
- ex: heart failure and liver failure
- therefore conditions in which there is total ECF excess but decreased ECV continue to stimulate volume sensors to promote further salt and water retention
water rentention is influenced by what two things
- thirst
- ADH
salt retention is influenced by
- renin-angiotensin system**
- ANP and catecholamines
What are some treatment options for volume overload
- dietary sodium restriction
- fluid restriction (hyponatremic)
- diuretics
- avoid offending medications
- promote sodium retention: NSAIDs, corticosteroids, estrogens/androgens
danger zone of hyponatremia (level)
< 125
symptoms of hyponatremia
- weakness, lethargy
- anorexia, N/V
- muscle cramps, sz, coma
- death
what is the most common electrolyte abnormality in hospitalized patients
hyponatremia
What are some causes of hypervolemic hyponatremia
- CHF
- cirrhosis
- renal failure
- nephrotic syndrome
What are some causes of euvolemic hyponatremia
- SIADH ** (most common cause)
- diuretic use
- hypothyroidism
- adrenal insufficiency
What are some causes of hypovolemic hyponatremia with urine sodium < 10; FENa < 1%
-
urine Na < 10: extrarenal
- vomiting
- diarrhea
- hemorrhage
- excessive sweating
What are some causes of hypovolemic hyponatremia with urine sodium >10; FENa > 1%
- renal causes
- adrenal insufficiency
- diuretics
- salt wasting nephropathy: interstitial nephritis, PCKD
- partial urinary tract obstruction
if patient presents with hyponatremia, need to r/o pseudohyponatremia. What is it
- serum Na < 135 but normal osmolality
- due to hyperlipidemia or hyperproteinemia, with decrease in aqueous portion of plasma
if patient presents with hyponatremia, need to r/o hyponatremia due to hyperosmolar state. What can cause this
- increased glucose in ECF causes shift of water from ICF to ECF thus lowering serum Na
Na drops how much for every 100mg/dl rise of plasma glucose
1.5mmole/L
if hyponatremia with hypovolemia is a chronic process, rapid correction may cause what
- osmotic demylination
- neurologic morbidity or mortality
- no more than 10 mEq/L increase in 24 hours
small cell carcinoma of lung can cause what condition that can result in hyponatremia
SIADH
List the etiologies of SIADH
- neuropsychiatric disorders
- malignancies
- pulmonary disorders (small cell CA lung)
- drug induced:
- carbamezepine, tricyclic antidepressants, antineoplastic agents, narcotics
List the 4 characteristics of SIADH
- serum osmolarity below normal
- inappropriately concentrated urine
- euvolemia
- normal renal, adrenal, and thyroid function
treatment of SIADH induced hyponatremia
fluid restriction
treatment of hypervolemic hyponatremia
- manage underlying disease
- sodium and water restriction
- diuretics
what sodium lab value should warrant hospitalization
Na < 125
overall, if patient has hypervolemic or euvolemic hyponatremia, first line of tx is
restrict fluids
overall, if patient has hypovolemic hyponatremia, first line of tx is
replace fluid, usually with isotonic saline
what is the traditional treatment of chronic hyponatremia
- demeclocycline
- induces nephrogenic diabetes insipidus
clinical presentation is consistent with
- thirst
- restlessness
- irritability
- AMS
- sz
- muscle twitching
- hyperreflexia
- ataxia
hypernatremia
- clinical features due to brain shrinkage secondary to increased ECF osmolality
what are the big picture causes of hypernatremia
- too little dietary water
- too much dietary salt
- excessive water loss from body
name some conditions or situations that will cause hypovolemic hypernatremia
- loss of solute-free water
- renal: loop diuretics, osmotic diuresis
- extrarenal: osmotic diarrhea, sweat
in response to hypernatremia, the body’s homeostatic mechanism would normally
- create thirst and increase fluid intake
- maximally concentrate the urine to prevent further water loss
list the body’s homeostatic priorites in order
- volume
- pH
- electrolytes
what is central diabetes insipidus
- impaired secretion of ADH
- see nonosmotic urinary water loss in setting of elevated serum sodium (urine is dilute when it should be concentrated)
what is nephrogenic diabetes insipidus
- lack of kidney response to ADH causing continued water loss even though patient is low on water
- adequate ADH is present
list some causes of acquired nephrogenic diabetes insipidus
- chronic renal insufficiency
- tubulointerstitial renal disease
- amyloidosis
- lithium toxicity
- hypercalcemia, hypokalemia
in diabetes insipidus, a urine osmolarity of what indicated impaired release or action
<500 mOsm/kg
Giving vasopressin will increase urine osmolality in which form of diabetes insipidus
central DI
tx options for nephrogenic Diabetes insipidus
- thiazide diuretics
- amiloride (potassium sparing diuretic)
- chlorpropamide
Why should a patient with hypernatremia present for several days not be given water too rapidly
- could result in rapid shift of water into brain cells causing seizures or brain damage
- central pontine myelinolysis (osmotic demyelination)
how do you calculate water deficit
- water deficit = normal TBW - current TBW
- normal TBW = 0.6 x body weight in Kg
- current TBW = (normal serum Na x normal TBW / measured serum Na)
name some conditions or situations that will cause hypervolemic hypernatremia
- excess sodium and extracellular volume expansion
- excess saline or sodium bicarb
- exteral or parenteral feeding without free water
name some conditions or situations that will cause euvolemic hypernatremia
- loss of fluid low in sodium and potassium
- diabetes insipidus
- central:
- head trauma, inflammatory, neoplastic, infiltrative
- nephrogenic
- congential or acquired defect of vasopressin 2 receptors
- central:
treatment of hypovolemic hypernatremia
- rehydrate
- isotonic solution initially then hypotonic
treatment of euvolemic hypernatremia
- rehydration
- D5 or 1/2 normal saline
treatment of hypervolemic hypernatremia
loop diuretics
