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MOHD Keystone Exam 2 > #34 - Water balance > Flashcards

#34 - Water balance Flashcards

1
Q

what is total body water, how is it divided?

A

total body water= 60% of body weight.

65% is intracellular fluid,

35% extracellular fluid (28% interstitial, 7% plasma)

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2
Q

which 3 systems work together to maintain plasma osmolality within a tight range?

A
  • ADH
  • thirst (access to water)
  • renal function
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3
Q

hypernatremia and hyponatremia are disorders of __/

A

water homeostasis.

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4
Q

Algorithm for assessing hyponatremia

A

1 - look at plasma osmolality!!

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5
Q

T/F - Osmolality throughout the body (in all compartments) is generally the same.

A

True. This is because, outside the kidney, water moves freely across all body fluid compartments.

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6
Q

What are the primary determinants of plasma osmolality?

A
  • glucose
  • sodium
  • BUN
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7
Q

normal plasma osmolality

A

280-290

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8
Q

what is the plasma osmolality at which ADH starts to be secreted?

A

280 and above

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9
Q

what is the basic equation for serum Na

A

serum Na = total body Na/ total body H20

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10
Q

what is the equation for Posm?

A

2*Na + glu/18 + BUN/ 2.8

notice that Na is multiplied while the other factors are divided.

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11
Q

Case:

  • hyponatremia
  • high plasma osmolality

likely cause

A 
hypertonic hyponatremia - 
-> common cause = diabetes
high glucose pulls water out of cells, 
diluting serum Na. 
But glucose is part of osmolality, 
so osmolality remains high.
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12
Q

symptoms of low osmolality

A

cerebral edema –> neurologic symptoms!

  • mental status change
  • seizure
  • brain herniation due to swelling
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13
Q

case:
- hyponatremia
- low Posm

Next step?

A
  • proceed down the algorithm:
  • determine if it is ADH mediated or ADH independent
  • if ADH mediated, what is the volume status?
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14
Q

describe the algorithm for hyponatremia

A

hyponatremic patient

  • order plasma osmolality (should be low)
  • determine if ADH mediated or ADH independent

-if ADH mediated, determine the volume status.

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15
Q

Causes of ADH independent hyponatremia

A
  • low solute diet
  • excessive water drinking (intake exceeds kidney’s ability to make dilute urine)
  • renal failure (no urine output)
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16
Q

cause of ADH dependent natremia

A

kidney is unable to make a dilute urine, due to ADH. Makes small concentrated urine at the wrong time.

17
Q

3 triggers of ADH release

A
  • high osmolality
  • decrease in blood pressure/ volume (perceived or real)

-nonphysiologic (SIADH = syndrome of inappropriate ADH)

18
Q

What happens to the ADH set point in volume depleted / low BP states?

A

ADH set point is lowered, and the curve is steeper.

ie, it will start to be released starting at Posm =270 instead of 280, and more will be released quicker.

19
Q

Define SIADH (diagnostic criteria)

A
  • low serum osmolality (+hyponatremia)
  • inappropriately concentrated urine
  • -euvolemia
20
Q

What causes SIADH? - 3 categories

A

Numerous causes, but 3 big ones are:

  • pulmonary disease
  • cancer
  • medications
21
Q

How do you determine if hyponatremia is ADH dependent or ADH independent?

A

look at urine osmolality!!
-ADH independent will have low urine osmolality

-ADH dependent will have (inappropriately) high urine osmolality.

22
Q

How do you assess volume status?

A
  • difficult
  • with physical exam
  • tachycardia, orthostatic hypotension
23
Q

treatment for hyponatremia: who gets treated?

A

if symptomatic (altered mental status), treat aggressively.

if asymptomatic, just limit fluids.

24
Q

3 hyponatremia causes that are likely to be acute and need treatment

A
  • water intoxication
  • post-operative
  • thiazide diuretics
25
Q

Treatment approach in symptomatic hyponatremia

A
  • treat with isotonic saline or hypertonic saline (hypertonic corrects faster.)
  • GO SLOW!!!!!!!!
  • correct a maximum of 10-12 meq over the first 24 hours (0.5meq/hr)
26
Q

What happens if you correct hyponatremia too fast?

A

osmotic demyelination

27
Q

main causes of hypernatremia

A
  • excess losses (sweat / fever, vomit, diarrhea, hyperventilation, etc)
  • lack of intakes (eg intubation)
28
Q

symptoms of hypernatremia

A

basically the same as hyponatremia

  • neurological deficit, change of mental status
  • seizures/coma
29
Q

Treatment approach for hypernatremia

A
  • estimate water deficit, and replace it (with D5W or plain water) GRADUALLY over 48-72 hours.
  • frequently monitor labs to make sure they are improving.
  • estimate ongoing water losses, and replace those too.
30
Q

2 categories of hypernatremia

A
  • low urine output (not drinking enough)
  • high urine output

high Uosm = hyperglycemia, loop diuretics low Uosm =
diabetes insipidus lack of ADH)

31
Q

categories of high urine output hypernatremia - what causes it?

A

high Urine osmolality >300= hyperglycemia, loop diuretics

low Uosm

MOHD Keystone Exam 2 (14 decks)

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