1: Sodium Flashcards
Sodium normal range
135-145 meq/L
Equation for calculating plasma/serum osmolality
Na x2 + BUN/2.8 + Glc/18 (note that Na is main contributor)
Major cause of sodium imbalance
Almost always a water issue, not a salt issue.
Hyponatremia symptoms and their overall etiology
Extracellular hypoosm –> brain swelling. <115: obtundation, seizures, coma
Why might a patient have a sodium of 110 and be asymptomatic?
Chronic issue, developed gradually –> time to adjust
Symptoms of hypernatremia and cause
Hyperosm –> brain cell shrinkage –> possible rupture of cerebral vessels, lethargy, weakness, irritability, twitching, seizures, coma, death
ADH produced where? Stored where? How does secretion work?
Prod in hypothalamus in supraoptic and paraventricular nuclei, stored in sec granules which move down supraopticohypophyseal tract to post lobe of pituitary
Osmotic stimuli for ADH release
Increased plasma osmolarity
Non-osmotic stimuli for ADH
Baroreceptors signaling hypovolemia or dec ECV (effect. circ vol), pain (alters Na level), esophageal (tumors, intubation), meds
What type of vasopressin do humans have?
Arginine
ADH cascade
ADH binds V2 receptor (collecting tubules) -> act protein kinase -> AQP2 to luminal membrane
What can you evaluate to determine the kidney’s thoughts on body volume status?
Urine sodium: high = kidney behaving as though body is volume expanded. Low is vice versa
Normal urine osm range?
50-1400 in normal functioning kidney
What Uosm indicate ADH vs no ADH present?
100 = varying degrees of ADH activity
What determines max and min daily urine output? What is the usual mOsm load?
Daily osmolar load and urine osmolarity. Usual daily = 500-750 mOsm
Minimum vol water excreted daily (calculate)
Daily osm load/max Uosm = 500/1000 = 0.5 L daily
Max vol water excreted daily (calculate)
Daily osm load/ min Uosm = 750 mOsm/50 = 15 L/d
Which components respond to neurohumoral regulation?
Prox (Angiotensin II, dopamine, NE) and Collecting tubule (aldosterone, atrial natriuretic peptide)
How is reabsorption of sodium determined in the LoH and distal tubule?
Flow-dependent
What amount of urinary sodium is indicative of low vs high?
Low: < 10 meq/L
High: > 10 meq/L
Causes of hyponatremia with normal Posm
Hyperlipidemia, hyperproteinemia: these items take up more plasma space reducing plasma water space
Causes of hyponatremia with elevated Posm
Hyperglycemia, hypertonic mannitol: water shifts out of cells to reestablish equilibrium making Na more dilute
Osmotic stimuli to ADH -> plasma reg within 1%. How does hypoNa develop then?
Non-osmotic stim (baroreceptors) maintain ECF (effec circ vol) at expense of plasma osm
How much water would you have to drink/day to cause hypoNa?
10-15 L
How can you run into hyponatremia without excessive fluid intake?
Low osmolar load e.g. usually big beer drinkers not eating much else or “toast and tea” elderly
What might be some causes of hypoNa when volume depleted?
GI (n/v/d), skin losses (burns), diuretics, pure cortisol deficiency
When might you have hypoNa with UNa <10 and be volume expanded?
Kidney/baroreceptors perceive reduced ECV e.g. CHF, cirrhosis/liver failure, nephrotic syndrome
HypoNa with UNa >10 and volume depleted: what is this called? Causes?
Salt wasting. Adrenal insufficiency, renal disease, diuretics, hypothyroid, hypoK w met alkalosis after vomiting (Na loss with bicarb)
HypoNa with UNa >10 and vol approp or expanded: causes?
Excess ADH production e.g. SIADH, reset osmostat, CKD
Causes of SIADH
Tumors (oat cell), pulmonary (TB, pneumonia, asthma), drugs, esophageal, pain, neuropsych
What happens in SIADH
Fixed ADH excretion w/o regard to osm or vol stimuli, fixed Uosm at high level
SIADH treatment
Fluid restriction, inc osm load diet via sodium or protein.
Hyponatremia treatment
Give NS to replenish volume and turn off ADH
Severe hyponatremia treatment
hypertonic saline (3% = 513 meq Na/L) to get out of danger zone
Volume expanded hyponatremia treatment
ADH antagonist “-vaptans” e.g. Tolvaptan or Conivaptan
What is the “danger range” of hyponatremia? Over what time period should someone be corrected out of this?
115-120, correct over several hours (more slowly for the more chronic)
Once out of danger range, how quickly should you correct hyponatremia?
12meq/L over 24 hours (0.5 meq/L/hour). This is the same rate at which you correct hypernatremia.
What is the risk of rapid hyponatremia correction?
Demyelination of pons/ osmotic demyelination syndrome
Treatment for hyponatremic seizures
100 cc 3% NaCl over 10 min
Treatment for hyponatremic neurologic non-seizure symptoms
30-50 cc 3% NaCl/hour for several hours
V1a and V1b ADH receptors involved in ___ (2)
vasoconstriction and ACTH release
V2 ADH receptors involved in
Water channels moving into the luminal membrane
Which ADH antagonist has a limit on duration of treatment? Why?
Tolvaptan <30 days due to risk of liver failure
What is max UOsm in humans?
800-1400, corresponds to urine SG of 1.025 to 1.030
What UOsm constitutes severe CDI or NDI during hypernatremia?
<300 UOsm
What is central diabetes insipidus?
hypothalamus or pituitary not releasing ADH -> can’t reabsorb free water
What is nephrogenic DI?
Collecting tubules don’t respond to ADH
What is the action of renal prostaglandins on ADH response?
PG impairs ADH response -> inc water loss. NSAIDs decrease this.
In what situation would dDAVP be given for DI treatment?
Central DI. dDAVP is ADH, giving extra won’t make a difference in nephrogenic DI.
How do you determine treatment of hypernatremia?
Replace calculated water deficit over 60 hours
Equation for calculating free water deficit
(%body water) x (mass) x {([Na]/140) -1}
Standard % body water for males and females
males: 60%, females: 50%
Fluid used for hypernatremia treatment
Water PO or D5W IV
When would you use NS with hypernatremia?
Concomitant fluid loss and hypotension. Use NS until tissue perfusion improves
