TBL - Na Disturbances

Question 1

What is the normal concentration of sodium in plasma?

Answer 1

135-145 mEq/L

Question 2

What equation relates plasma sodium and total body water?

Answer 2

P(Na) =
TBe (Na + K) / TBW

Where TBe = total body exchangeable

Question 3

What is the definition of hyponatremia?

Answer 3

Plasma sodium

< 135 mEq/L

Question 4

What are clinical findings of hyponatremia?

Answer 4

Neurological dysfunction from swelling of brain cells

Consequences:
N/V
Headaches/lethargy
Seizures, coma, death

Question 5

What are major causes of hyponatremia?

Answer 5

Hypervolemic, hypotonic

Normovolemic, hypotonic

Hypovolemic, hypotonic

Question 6

Describe hypervolemic, hypotonic condition

Answer 6

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

Question 7

Describe the normovolemic, hypotonic condition

Answer 7

Euvolemic

Examples:
Syndrome inappropriate ADH (SIADH) = don’t develop edema and leads to increased mechanisms to increase sodium excretion

Question 8

Describe the hypovolemic, hypotonic condition

Answer 8

Mechanism: volume loss

Replacing volume with hypotonic fluids = dec. plasma sodium

Question 9

For hypervolemic and normovolemic conditions, what treatments are available?

Answer 9

Water restriction

Loop diuretics

Vasopressin antagonists

Impair ADH action

Question 10

What do loop diuretics do?

Answer 10

Decrease medullary gradient (what kidneys need to reabsorb water) = ADH can’t work as well to retain water

Question 11

Describe vasopressin antagonists

Answer 11

Conivaptan
Blocks V1 receptors
(Blood vessels for constriction)
Blocks V2 receptors 
(On kidney for water reabsorption)

Tolvaptan
Blocks V2 receptors

Question 12

What drugs impair ADH action?

Answer 12

Lithium

Demeclocycline

Question 13

How is hypovolemic, hypotonic condition treated?

Answer 13

Sodium replacement with fluids

Must calculate

Question 14

What are the steps for sodium replacement with fluid to treat hypovolemic, hypotonic condition?

Answer 14

(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

Question 15

How do you calculate TBW?

Answer 15

Volume of Na distribution * body weight

0.6 * weight (kg)

Question 16

Define hypernatremia

Answer 16

Plasma sodium

> 145 mEq/L

Question 17

What are clinical findings of hypernatremia?

Answer 17

Neurological dysfunction from water leaving cells and causing them to shrink

Consequences:
Lethargy
Weakness
Seizures, coma, death (higher levels)

Question 18

What are major causes of hypernatremia?

Answer 18

Water loss in excess of sodium and/or potassium loss

Renal loss:
+ diabetes insipidus
+ loop diuretics

GI loss

Question 19

What is diabetes insipidus?

Answer 19

Problem with ADH leads to increased loss of water in urine

Question 20

Differentiate between central diabetes insipidus and nephrogenic problem

Answer 20

Central DI =
Something wrong with brain leads to ADH deficiency

Nephrogenic problem =
Problem with V2 receptors leads to ADH resistance in kidney

Question 21

What are treatments for hypernatremia?

Answer 21

Give water

For central DI = desmopressin

For nephrogenic DI = thiazide diuretics

Question 22

How do thiazide diuretics help treat hypernatremia associated with nephrogenic DI?

Answer 22

Trigger inc. PT water reabsorption in order to decrease water delivery to CD = results in dec. ADH effects

Question 23

What are steps for calculating amount of water to give to treat hypernatremia?

Answer 23

(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…)”