B5.057 Electrolyte Abnormalities

Question 1

distribution of body water

Answer 1

total body water (TBW) = 60% of body weight
extracellular fluid = 20 % BW (5% plasma, 15% interstitial)
intracellular fluid = 40% BW

Question 2

2 methods to calculate total body water

Answer 2

BW * 0.6
OR
0.72 * BW * (1- %fat)

Question 3

why is there a different method depending on fat content

Answer 3

fat cells contain less water

more accurate to say TBW is 72% of lean body mass

Question 4

average TBW in a person weighing 70 kg with 17% body fat

Answer 4

41.83 L

Question 5

how to calculate distribution of TBW

Answer 5

2/3 intracellular
1/3 extracellular
-1/4 plasma
-3/4 interstitial

Question 6

variations of body fluid with age

Answer 6

preterm infants 85% TBW (less in cells)
neonates 80% TBW
adults 60% TBW
elderly 50% TBW

Question 7

significance of body fluid variation with age

Answer 7

problems with dehydration more common in neonates and elderly

Question 8

body fluid variation with gender

Answer 8

women higher % of body fat so lower % TBW

Question 9

forces involved in movement of water between body compartments

Answer 9

hydrostatic pressure (MAP)
osmotic/oncotic pressure (protein content)

Question 10

water movement between ECF and ICF

Answer 10

driven by osmotically active solutes

Question 11

water movement within ECF (vascular > interstitium)

Answer 11

depends on hydrostatic and oncotic pressure (Starling forces)

Question 12

what compartment does water enter the circulation in

Answer 12

plasma

Question 13

what is osmotic pressure

Answer 13

minimum pressure that needs to be applied to a solution to prevent inward flow of its pure solvent across a semipermeable membrane

Question 14

oncotic pressure

Answer 14

osmotic pressure exerted by proteins

Question 15

summary fluid movement across capillaries

Answer 15

fluid leaves arteriolar end of capillaries by outward hydrostatic pressure
fluid returns to plasma at venous side of capillaries due to inward force of oncotic pressure

Question 16

what is the significance of the Starling forces at work in capillaries

Answer 16

constant recycling of fluid between plasma and interstitium

Question 17

describe transcellular water movement

Answer 17

oncotic pressure draws water into the cell
water flows out of the cell following Na+ via Na/K ATPase (prevents cell from bursting)
ions distribute according to their electrochemical equilibrium (concentration and charge both taken into account)

Question 18

discuss the role of sodium in body fluids

Answer 18

key role in water movement
main extracellular cation and value is double from an osmotic perspective due to sodium attending anions (bicarb and Cl-)

Question 19

what % of ATP is used for Na/K ATPase function

Answer 19

60%!!!!
hella important y’all
hi leesy

Question 20

tonicity

Answer 20

defines the effect a solution has on the steady state volume of a cell

Question 21

hypotonic

Answer 21

final cell volume greater than initial

Question 22

isotonic

Answer 22

final cell volume same as initial

Question 23

hypertonic

Answer 23

final cell volume smaller than initial

Question 24

osmolality

Answer 24

number of solute molecules in solution

does not predict how a cell will respond to solution

Question 25

iso-osmotic but hypotonic solution

Answer 25

EX: permeant solute cell in 290 mOsm urea urea enters cell by diffusion, increasing intracellular solute concentration water enters cell causing it to swell and eventually rupture

Question 26

hyperosmotic but hypotonic solution

Answer 26

EX: permeant solute cell in 580 mOsm urea cell initially shrinks as water rapidly leaves cell, intracellular osmolality increases to 580 mOsm urea enters cell by diffusion, increasing intracellular solute concentration water enters cell causing it to swell and eventually rupture

Question 27

hyperosmotic but isotonic solution

Answer 27

cell in 290 mOsm NaCl + 290 mOsm urea cell shrinks initially as water leaves and intracellular osmolality increases to match extracellular urea enters cell and water follows until cell returns to normal volume and intracellular urea concentration is 290 mOsm

Question 28

examples of hypotonic solutions

Answer 28

all solution with less than the osmolality of normal plasma (290 mOsm) all solution that contain only permeant solutes solution containing both impermeant and permeant solute when osmolality due to the impermeant solute is less than 290

Question 29

examples of isotonic solutions

Answer 29

all solutions containing only impearmeant solutes with osmolality equal to the osmolality of normal plasma solutions containing both impermeant and permeant solute when osmolality due to impermeant solute equals the osmolality of normal plasma

Question 30

examples of hypertonic solutions

Answer 30

all solutions containing only impermeant solutes with osmolality greater than that of normal plasma solutions containing both impermeant and permeant solute when osmolality due to impermeant solute is greater than the osmolality of normal plasma

Question 31

hypotonic expansion

Answer 31

``` excessive H2O intake ECF osmolality - decrease ECF volume - increase ICF osmolality - decrease ICF volume - increase ```

Question 32

hypotonic contraction

Answer 32

``` kidneys excreting too much salt (removal of salt in excess of water) ECF osmolality - decrease ECF volume - decrease ICF osmolality - decrease ICF volume -increase ```

Question 33

isotonic expansion

Answer 33

``` IV normal saline infusion ECF osmolality - no change ECF volume - increase ICF osmolality - no change ICF volume - no change ```

Question 34

isotonic contraction

Answer 34

``` hemorrhage ECF osmolality - no change ECF volume - decrease ICF osmolality - no change ICF volume -no change ```

Question 35

hypertonic expansion

Answer 35

``` drinking sea water ECF osmolality - increase ECF volume - increase ICF osmolality - increase ICF volume - decrease ```

Question 36

hypertonic contraction

Answer 36

``` severe sweating (removal of water in excess of salt) ECF osmolality - increase ECF volume - decrease ICF osmolality - increase ICF volume - decrease ```

Question 37

compensation for hypotonic expansion(hyponatremia)

Answer 37

decreased H2O intake increased H2O output decreased Na+ output ECF to ICF fluid shift

Question 38

what is water intoxication

Answer 38

acute dilutional hyponatremia | movement of water into brain cells causes neurological symptoms

Question 39

compensation for hypotonic contraction

Answer 39

``` decreased H2O intake increased Na+ intake increased H2O output (decreased ADH) decreased Na+ output (via R-A-A) ECF to ICF fluid shift ```

Question 40

compensation for hypertonic expansion (hypernatremia)

Answer 40

increased H2O intake decreased H2O output increased Na+ output ICF to ECF fluid shift

Question 41

discuss hypertonic expansion in the context of hyponatremia

Answer 41

pseudohyponatremia due to increased concentration of another solute (glucose, ureas, etc.) normal total body sodium but increased osmolality

Question 42

compensation for hypertonic contraction

Answer 42

increased H2O intake decreased H2O output increased Na+ output ICF to ECF shift

Question 43

Na+ deficit

Answer 43

amount of NaCl necessary to raise plasma Na+ to the desired value

Question 44

Na+ deficit formula

Answer 44

Na+ deficit = TBW * (desired Na+ - present Na+)

Question 45

calculation of H2O deficit

Answer 45

normal TBW * normal Na+ = current TBW * current Na+ | water deficit = present TBW * [(current Na+/normal Na+) - 1]

Question 46

when can hyponatremia occur

Answer 46

hypotonic expansion - increased H2O hypotonic contraction- increased Na+ loss water in excess of solute

Question 47

hyponatremia with plasma hypertonicity

Answer 47

severe hyperglycemia hypertonic mannitol hyperproteinemia (myeloma)

Question 48

hyponatremia with plasma hypotonicity

Answer 48

``` renal failure edematous states thiazides SIADH endocrine genetic (Bartter, Gitelmans) ```

Question 49

signs and symptoms of hyponatremia

Answer 49

frequently asymptomatic symptomatic < 120 usually CNS symptoms: lethargy, weakness, confusion, delirium, seizures

Question 50

diagnosis of hyponatremia

Answer 50

1. severe w seizures or less severe, water restriction if less severe 2. exclude pseudohyponatremia 3. investigate hyponatremia with hypotonicity (renal water excretion, excess free water sources) 4. identify signs of ECFV depletion or overload

Question 51

treatment of hyponatremia with increased tonicity

Answer 51

usually due to hyperglycemia | 0.9% saline until stable, then 0.45%

Question 52

treatment of renal failure hyponatremia

Answer 52

water restriction

Question 53

treatment of ECFV depletion hyponatremia

Answer 53

0.9% saline

Question 54

treatment of edematous hyponatremia

Answer 54

water restriction sodium restriction diuretics to remove edema

Question 55

treatment of increased ADH hyponatremia

Answer 55

water restriction | treat cause

Question 56

treatment of endocrine hyponatremia

Answer 56

treat hypothyroidism | correct adrenal failure

Question 57

when can hypernatremia occur

Answer 57

hypertonic expansion- increased Na+ intake hypertonic contraction- decreased H2O solute in excess of water

Question 58

reasons for hypernatremia

Answer 58

extra renal water loss (sweat, burns, GI) renal water loss (osmotic diuresis, DI) excess sodium (iatrogenic, Liddles)

Question 59

signs and symptoms of hypernatremia

Answer 59

w dehydration: orthostatic hypotension and oliguria altered mental status w severe hyperosmolality: hyperthermia, delirium, coma

Question 60

diagnosis of hypernatremia

Answer 60

1. find reason for water loss or Na+ gain 2. find why patient is unable to replace water loss 3. identify if polyuria is present

Question 61

treatment of hypernatremia

Answer 61

1. correct severe ECFV depletion with 0.9% saline, continue with hypotonic fluid 0.45% 2. calculate water deficit and administer water replacement at a rate sufficient to correct hyponatremia but slowly enough to avoid cerebral edema