TBL - Na Disturbances Flashcards
What is the normal concentration of sodium in plasma?
135-145 mEq/L
What equation relates plasma sodium and total body water?
P(Na) =
TBe (Na + K) / TBW
Where TBe = total body exchangeable
What is the definition of hyponatremia?
Plasma sodium
< 135 mEq/L
What are clinical findings of hyponatremia?
Neurological dysfunction from swelling of brain cells
Consequences:
N/V
Headaches/lethargy
Seizures, coma, death
What are major causes of hyponatremia?
Hypervolemic, hypotonic
Normovolemic, hypotonic
Hypovolemic, hypotonic
Describe hypervolemic, hypotonic condition
Edematous
Examples: cirrhosis (ascites), HF (pulmonary, peripheral edema)
Mechanism:
Dec. ECV = inc. Na/H2O retaining mechanisms = inc. symp, RAAS, ADH = water in excess of sodium = drop in plasma sodium
Describe the normovolemic, hypotonic condition
Euvolemic
Examples:
Syndrome inappropriate ADH (SIADH) = don’t develop edema and leads to increased mechanisms to increase sodium excretion
Describe the hypovolemic, hypotonic condition
Mechanism: volume loss
Replacing volume with hypotonic fluids = dec. plasma sodium
For hypervolemic and normovolemic conditions, what treatments are available?
Water restriction
Loop diuretics
Vasopressin antagonists
Impair ADH action
What do loop diuretics do?
Decrease medullary gradient (what kidneys need to reabsorb water) = ADH can’t work as well to retain water
Describe vasopressin antagonists
Conivaptan Blocks V1 receptors (Blood vessels for constriction) Blocks V2 receptors (On kidney for water reabsorption)
Tolvaptan
Blocks V2 receptors
What drugs impair ADH action?
Lithium
Demeclocycline
How is hypovolemic, hypotonic condition treated?
Sodium replacement with fluids
Must calculate
What are the steps for sodium replacement with fluid to treat hypovolemic, hypotonic condition?
(1) calculate sodium deficit
Na deficit =
TBW [ P(Na)desired - P(Na)current ]
(2) calculate how much fluid required
= Na deficit / [Na] in fluid
(3) calculate time required
= [ P(Na)desired - P(Na)current ] / rate of correction
(4) calculate infusion rate
= volume of fluid / time
How do you calculate TBW?
Volume of Na distribution * body weight
0.6 * weight (kg)
Define hypernatremia
Plasma sodium
> 145 mEq/L
What are clinical findings of hypernatremia?
Neurological dysfunction from water leaving cells and causing them to shrink
Consequences:
Lethargy
Weakness
Seizures, coma, death (higher levels)
What are major causes of hypernatremia?
Water loss in excess of sodium and/or potassium loss
Renal loss:
+ diabetes insipidus
+ loop diuretics
GI loss
What is diabetes insipidus?
Problem with ADH leads to increased loss of water in urine
Differentiate between central diabetes insipidus and nephrogenic problem
Central DI =
Something wrong with brain leads to ADH deficiency
Nephrogenic problem =
Problem with V2 receptors leads to ADH resistance in kidney
What are treatments for hypernatremia?
Give water
For central DI = desmopressin
For nephrogenic DI = thiazide diuretics
How do thiazide diuretics help treat hypernatremia associated with nephrogenic DI?
Trigger inc. PT water reabsorption in order to decrease water delivery to CD = results in dec. ADH effects
What are steps for calculating amount of water to give to treat hypernatremia?
(1) calculate water deficit
= NBW * (1-140 / P(Na))
(2) calculate time required
= P(Na)current - P(Na)desired / rate of correction
(3) calculate infusion rate
= H2O deficit / time
= _______ + “ongoing insensible water loss (sweat, feces…)”
