Disorders of water balance

Question 1

Hypo and Hypernatremia refer to concentration of sodium in ___ NOT ABSOLUTE AMOUNT OF SODIUM IN BODY

Hyponatremia means

Answer 1

serum

too little sodium in the serum

Question 2

Kidney normally maintains serum osmolality between ___ and ___

Answer 2

280-295 mOsm/kg

Question 3

__ moves freely across cell membranes unlike electrolytes

Answer 3

water

Question 4

equation for serum osmolality

Answer 4

Sosm = 2xNa (mEq/L) + BUN (mg/dL) : 2.8 + Glucose (mg/dL): 18

Question 5

Situations with Hypertonicity

Answer 5

Hypernatremia
uremia
diabetic coma
unmeasured osmoles (alcohols, glycin)

Question 6

Much higher ___ with hypovolemia than with ___ although a relatively large fall in blood volume is required before this response is initiated

Answer 6

ADH with hypovolemia

hypervolemia

Question 7

what type of natremia will you see?
1) isotonic (lab artifact in severe hyperlipidemia or hyperproteinemia)

2) due to uncontrolled diabetes (water shift FROM ECF into blood) to cause hyponatremia)
3) MOST SIGNIFICANT

Answer 7

Hyponatremia

Hypertonic:

Hypotonic:

Question 8

Mechanism of osmoregulation

Answer 8

1) osmoreceptors detect incr osmotic pressure (hypothalamic neuron)

baroreceptors (aortic arch, carotid sinus), detect decr blood pressure

2) release ADH into posterior pituitary

3) causes vasoconstriction of blood vessels via V1 receptors
causes incr reabsorption of water in kidney via V2 receptors
4) restore plasma osmolarity, blood volume, blood pressure

Question 9

hypertonic hyponatremia most often due to ___

Answer 9

uncontrolled diabetes

Question 10

isotonic hyponatremia =

Answer 10

lab artifact

Question 11

clinically most significant form of hyponatremia

how does it develop

Answer 11

hypotonic hyponatremia

ADH

Question 12

Hyponatremia usually implies

Hypertonic usually implies

Hypotonic usually implies

Answer 12

1) lab artifact in severe hyperlipidemia or hyperproteinemia
2) uncontrolled diabetes (water shift)
3) significant

Question 13

1) ADH incr …
2) ADH incr exponentially if
3) ADH causes

Answer 13

1) if serum osmolality incr to bring back serum osmolality to normal
2) blood volume decr by more than 6-8% despite decr in serum osmolality leading to hyponatremia
3) water reabosrption in renal collecting ducts

Question 14

ADH normally does what

2) ADH incr if … to bring back…
3) ADH incr expontentially if …. despite decr in serum osmolality (___)

Answer 14

1) water reabsorption in collecting ducts
2) if serum osmolality increases to bring back serum osmolality to normal

if blood volume decreases –> hyponatremia

Question 15

How can blood volume decr

How does kidney respond to decr blood volume

Answer 15

1) hemorrhage

2) plasma volume and ECF losses
a) GI loss
b) renal loss (XS diuretics, osmotic diuresis= uncontrolled diabetes, minearlocorticoid deficiency)
c) XS sweating
d) loss sodium and water

ADH is released

Question 16

if blood volume decr this is called…

Answer 16

hypovolemic hyponatremia

Question 17

signs of decr blood volume

Answer 17

1) low blood pressure and tachy
2) orthostatic hypotension
3) thirst, weakness, lethargy
4) dry skin and muc membranes
5) low urine output, concentrated urine, low urine Na concentration (

Question 18

low urine output, concentrated urine, low urine Na concentration (

Answer 18

decr blood volume

Question 19

define hypovolemia

Answer 19

decr total body sodium (and total water but less because compensatory ADH)

Question 20

how to treat hypovolemic hyponatremia

Answer 20

restore blood volume

1) give normal saline to decr ADH

Question 21

causes of decr “effective blood volume”

how does kidney compensate

Answer 21

decr organ perfusion from

1) weak heart (CHF)
2) XS vasodilation (liver cirrhosis)

incr tubular Na and water reabsorption, excess total body sodium and water –> edema

Question 22

sign of decr effective blood volume

Answer 22

edema

Question 23

describe hypervolemic hyponatremia

in hypervolemic hyponatremia there is excess __ and even more excess __

Answer 23

1) severe CHF and liver cirrhosis
2) ADH stim
3) more water reabsorption in collecting duct
4) hyponatremia

sodium (edema) and total body water

Question 24

2nd mechanism beside ADH release for hypervolemic hyponatremia

Answer 24

intrinsic kidney disease
1) either diluting mechanism in distal tubules nonfunctional or

or
2) RBF and GFR too low (advaced CKD)

Question 25

thiazide diuretics impair dilution and cause hyponatremia in which patient groups

why?

Answer 25

elder

hypo-
hyper-
euvolemic

block thiazide transporter in distal convoluted tubule so urine not sufficiently dilute

Question 26

requirements for normal dilution system (3 areas)

Answer 26

1) ascending limb of loop of henle and distal convoluting tubule
in distal tubule still have NaCl reabsorption via thiazide sensitive NaCl transporter to dilute more

2) delivery of tubular fluid to distal diluting segment of nephron (normal GFR)
3) suppression of ADH

Question 27

free water excretion capacity is ___ of GFR

max urinary dilution = ___

Answer 27

20% of GFR

50 mOsm/kg

Question 28

situations leading to hypervolemic hyponatremia

Answer 28

1) edema
2) ascites
3) pleural effusions
4) hx of heart, kidney, liver disease
5) weight gain in short time

Question 29

treatment of hypervolemic hyponatremia

Answer 29

water and sodium restriction + loop diuretics (stop thiazides)

treat underlying
inotropes for CHF

DON’T GIVE SALT !!!!!

Question 30

DEFINE EUVOLEMIC hyponatremia

examples of causes

Answer 30

due to excessive ADH secretion

1) hypothyroidsim and adrenal insufficiency
2) nausea, pain, psychosis
3) SSRI’s antipsychotics, NSAIDS

Question 31

define SIADH

causes

Answer 31

syndrome of inappropriate ADH secretion after ruling out other causes

euvolemic hyponatremia and urine NOT maximally dilute (>50-100 mOsm/kg)

due to carcinomas (SCLC cancers, ectopic ADH)
CNS disorders
pulm diseases

Question 32

symptoms of hyponatremia

why does cerebral edema develop?

Answer 32

1) anorexia, n/v
2) weakness, lethargy, confusion
3) seizures, death from cerebral edema

intracellular osmolarity in brain > serum osmolarity so H2O flow from blood into brain

Question 33

treatment of euvolemic hyponatremia
1) if seizures, give

2) if asymptomatic
3) if hyponatremia is chronic (> 48 hrs) or unknown duration

Answer 33

1) hypertonic saline
2) water restriction and correct underlying disorders/remove drugs
3) slow correction of Na to avoid central pontine myelinolysis (osmotic demyelination syndrome)
4) ADH antagonists = last resort

Question 34

when would a patient get central pontine myelinolysis (osmotic demyelination syndrome)

Answer 34

if you correct their chronic euvolemic hyponatremia too fast

if serum Na is corrected too rapidly, blood entering brain ishypertonic compared to brain cells
water flows out of brain into blood cell —> shrinks the brain (esp pons and medulla)

Question 35

hypernatremia is a disorder of ___ not ___

Answer 35

water balance NOT SODIUM

Question 36

when would hypernatremia develop ?

why?

Answer 36

incr in serum osmolality –> severe thirst (disorder of water balance)

if patient does not have access to water (hospitalized)

or CNS pathology imparing thirst

Question 37

what causes hypernatremia

Answer 37

1) renal/extrarenal water loss > sodium loss (HYPOVOLEMIC HYPERNATREMIA)
2) addition of hypertonic fluids (hypervolemic hypernatremia (iatrogenic) = hypertonic saline, TPN, or bicarb
3) lack of ADH effect = diabetes (water diuresis, dilute urine) because no ADH or kidney resistant to ADH

Question 38

why does diabetes insipidus lead to hypernatremia

manifest as?

Answer 38

1) ADH deficiency
2) kidney don’t respond to ADH

–> polyuria and polydipsia

Question 39

describe ADH deficiency (central diabetes inspidius)
1) diseases of …

2) most are caused by …
3) Do kidneys still respond to exogenous ADH
4) treatment

Answer 39

1) hypothalamus or pituitary gland (head trauma, surgery, tumors, encephalitis)
no ADH secreted

2) idiopathic
3) kidney still respond to exogenous ADH
4) long acting nasally administered analogue (DDAVP)

Question 40

ADH resistance (nephrogenic diabetes inspidius)

1) renal collecting duct does not…
2) exogenous ADH will/will not raise Uosm
3) congental nephrogenic DI due to which 2 mutations
4) symptoms in infants…

Answer 40

1) renal collecting duct not respond to ADH
2) exogenous ADH NOT RAISE Uosm
3) mutation in AVP-receptor (V2R) = XLR or aquaporin 2 gene (AR or AD)
4) failure to thrive, polyuria, fever, vomiting, seizures, death

Question 41

acquired nephrogenic DI
1) more or less common than congenital
more or less severe than congenital

2) causes are
3) long term therapy

Answer 41

1) more common, less severe
2) hypercalcemia, chronic hypokalemia

3) lithium
cidofovir, foscarnet, ampho B, ifosfamide

Question 42

CKD due to acquire nephrogenic DI causes … defect due to tubular dysfunction and ADH resistance

2 diseases that cause early concentrating defect by disrupt medulla

__ causes ADH resistance

Answer 42

1) concentrating defect
2) sickle cell anemia, polycystic kidney disease
3) urinary obstruction

Question 43

describe gestational DI and how it occurs

treatment

Answer 43

1) release of vasopressinase from placenta in 2nd half of pregnancy
2) DDAVP

Question 44

symptoms of hypernatremia

Answer 44

1) extreme thirst
2) neuromuscular irritability = twitch, seziure
3) AMS

Question 45

treatment of hypernatremia

2) give ___ in most cases not half normal saline
3) ___ if hypernatremia > 48 hrs
4) for chronic management, __ helpful

Answer 45

1) replace water deficit
2) give D5W not half-normal saline
3) slow correction if hypernatremia is present for > 48 hrs
4) thiazides to reduce polyuria

Question 46

equation for water needed

Answer 46

Water needed (L) = 0.6 x body weight (kg) x [actual Na:desired Na - 1]

Question 47

why does heart failure cause hyponatremia

Answer 47

1) CO and tissue perfusion are very low
2) sensed by baroreceptors in heart and kidney as decr effective blood volume
3) symp NS stim salt and water retention by kidneys
4) edema (XS total body water and total body sodium)

Question 48

why does liver cirrhosis cause hyponatremia

Answer 48

1) excessive vasodilation in splanchnic vasculature
2) sensed as decr effective blood volume
3) stim ADH ((XS total body water and total body sodium)

Question 49

pulm edema
ascites
pleural effusions

sign of hypo or hypernatremia

Answer 49

hyponatremia