L48 Flashcards
What are 2 relationships between Na and H2O that may yield hypernatremia?
Normal Na/↓H2O = euvol hyperNa
↓Na/↓↓H2O = hypovol hyperNa = drop in water out of proportion to salt loss
↑↑↑Na/↑H2O = hypervol hyperNa
What is the sensor for ECF volume?
Baroreceptors in the carotid sins and atrium
Watch for drop in BP: hemorrhage, vomiting, diarrhea
What is the response invoked by baroreceptors when sense drop in BP?
Catecholamines
RAAS
ADH (non-osmotic regulation)
Net: ↑Na + H2O reabsorbed
What are 3 scenarios that simulate a drop in effective circulating volume? Aka probably volume overloaded but all fluid is edema not in vasculature.
CHF
Cirrhosis
Nephrotic syndrome
Where are osmoreceptors located?
Ant hypothalamus
↑osm -> ↑ADH
Would you rather be hypovolemic or hyponatremic?
You will release ADH to repair hypovolemia and remain hypoNa
If you lose too much volume, you’ll suffer CV collapse before you notice the effects of low Na
Where is ADH made?
Supraoptic + paraventricular nuclei
Stored in the post pituitary
Mechanism of ADH
Binds V2 receptors in collecting duct
Causes aquaporin 2 to the apical surface - re-uptake of water
Urine gets concentrated
Describe hypovol hyperNa. What is the cause if U Na > 20?
Lost more H2O than Na - both dehydrated and intravasc vol depleted
U Na > 20 = renal problem b/c you should be holding on to that Na to retain water
- Either on diuretic
- Or intrinsic renal disease
What is the cause of hypovol hyperNa if U Na
U Na
Describe euvol hyperNa. Name the 3 possible causes.
Dehydrated (lost H2O) but normal intravasc vol (no change to amt Na)
- Diabetes insipidus
- Hypodipsia (no drinking enough)
- Extra-renal loss in lungs or skin
Describe 2 types of diabetes insipidus
- Central DI = ADH deficient
- Nephrogenic DI = ADH isn’t working at kidney
Either way, can’t concentrate urine so at risk for hyperNa
What are the 3 possible causes of hypervol hyperNa?
U Na > 20 - makes sense b/c you’re trying to lose water and salt
- Psych pt ate NaCl
- Doctor did it - infusion of saline or NaHCO3
- Hypertonic dialysis
Why would hyperNa state be maintained?
Can’t get water: obtunded, infant
Clinical presentation of hyperNa
AMS - range confusion -> coma, watch out for metabolic encephalitis
+/- muscle irritability
Explain encephalitis in acute and chronic response to hyperNa
Cells shrink b/c lost water to hypertonic environment
Acute = (under 24 hrs) +electrolytes to pull water back in, bad SE on cell fxn
Chronic = +non-electrolytes to hold water, harder to remove but less impact on fxn
Treat acute hypernatremia
Hydration
Treat chronic hyperNa
Worry!!! Osmotic demyelinating syndrome // cerebral edema
Correct:
- ↓1 mEq/L [Na+] / hr
- ↓2 mosm/kg H2O / hr
Treat DI
ADH replacement
Do you use diuretics for hypervol hyperNa pts?
RARE
Equation for calculating pts water deficit (aka how much you need to replace)
H2O def = 0.6 x weight kg x (plasma Na - 140/140)
