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Clinical 2 (Part B) > 19 - Electrolyte Disturbances > Flashcards

19 - Electrolyte Disturbances Flashcards

1
Q

What is the most common electrolyte imbalance?

A

hyponatremia

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2
Q

Total body stores of K+ is around ________ mmol

A

3000-4000 mmol

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3
Q

___% of K is intracellular

A

98

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4
Q

___% of K is extracellular

A

2

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5
Q

What is the ratio of Na and K in and out of cell?

A

3 Na+ out

2 K+ in

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6
Q

normal serum level of K+ ?

A

3.5-5 mmol/L

intracellular is 150 mmol/L

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7
Q

Elimination of K+ is usually ___% renally and __% GI

A

90% renally (secretion from distal tubules)

10% GI

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8
Q

What is potassium homeostasis affected by?

A
  • Hormones
  • Acid-base status
  • Hyperosmolality
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9
Q

What hormones affect potassium homeostasis?

A
  • insulin
  • catecholamines
  • aldosterone
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10
Q

How does insulin affect potassium homeostasis?

A

stimulates Na/K ATPase pump to transport K+ intracellularly

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11
Q

How does catecholamines (ex. epinephrine) affect potassium homeostasis?

A

Beta-receptor stimulation, which:

a) activates Na+/K+/ATPase pump, drives potassium intracellularly
b) causes glyconeogenesis - increases glucose - releases insulin, drives potassium intracellularly

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12
Q

How does aldosterone affect potassium homeostasis?

A
  • acts at distal tubule
  • increase urinary potassium excretion

*aldosterone antagonist cause K+ retention (ex. spironolactone - K+ sparing diuretic)

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13
Q

How does decreasing blood pH affect extracellular K+ ?

A

if pH decreases, extracellular k+ increases

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14
Q

How does increasing blood pH affect extracellular K+ ?

A

if pH increases, extracellular K+ decreases

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15
Q

How does hyperosmolality affect potassium ?

A

shifts to extracellular fluid

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16
Q

What is the definition lab value for hypokalemia?

A

K+ < 3.5 mmol/L

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17
Q

What is hypokalemia due to?

A

total body K+ deficit or intracellular shifting

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18
Q

What can moderately low hypokalemia cause?

A

-cramps, weakness, myalgias

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19
Q

What can severely low hypokalemia cause?

A

-EKG changes, arrhythmias, increased digoxin toxicity

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20
Q

What are the two common medication causes of hypokalemia?

A
  • thiazides

- furosemide

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21
Q

What can hypokalemia also be caused by? (2 things)

A

1) Excessive GI loss
- diarrhea
- vomiting
- metabolic alkalosis can develop and decrease serum K+
* if pH goes up, extracellular K+ decreases

2) Hypomagnesemia

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22
Q

How can hypomagnesemia cause hypokalemia ?

A
  • increases renal excretion of potassium

- important: need to correct underlying magnesium deficiency to correct

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23
Q

Non-pharms for hypokalemia treatment ?

A
  • adequate dietary intake of potassium (yogurt and potatoes)

- potassium salt substitutes

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24
Q

What is pharmacological Tx for hypokalemia?

A
  • Oral supplementation when mild, nausea/vomiting not a concern
  • IV replacement for severe hypokalemia, vomiting
  • replacement of magnesium first if hypomagnesemia (oral or IV)
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25
Q

What is the general rule of thumb for hypokalemia acute Tx?

A

100 mmol of oral replacement increases serum potassium by approx 1 mmol/L

ex. if patient has serum K+ of 2.8mmol/L, give 100 mmol to increase to 3.8 mmol/L

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26
Q

Describe oral Tx for hypokalemia

A
  • consider tablet vs liquid as tolerance can be an issue

- split doses to minimize GI irritation

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27
Q

Describe IV Tx for hypokalemia

A
  • severe hypokalemia
  • inpatient setting
  • high replacement rates need EKG monitoring (WRHA: infusions of > 15 mmol/hr)

*Cardiac monitoring required for infusions of > 15 mmol/hr

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28
Q

What are some common oral replacement products for hypokalemia?

A
  • Potassium chloride liquid - ex. 20 meq/dose (bitter taste but inexpensive, consider dissolving in juice)
  • Potassium citrate 25 meq oral tablets (effervescent, orange flavoured)
  • Potassium chloride 8 meq oral tablets/capsules (SlowK - do not crush, MicroK- can open up and sprinkle in apple sauce)
29
Q

For acute replacement for hypokalemia, how do we avoid GI irritation/nausea ?

A
  • avoid giving more than 24 meq (3 tabs) per dose or more than 50 meq or liquid per dose
  • wait at least 2 hours before giving additional doses
30
Q

For chronic replacement for hypokalemia (i.e. concurrent diuretic) how much oral replacement therapy can we give daily?

A

8-16 meq oral replacement therapy daily

31
Q

If the hypokalemia is diuretic-induced, what can we add?

A

concurrent K+ sparing diuretic (ex. spironolactone)

32
Q

Hypokalemia:

How do we monitor acute inpatient setting correcting severe hypokalemia?

A
  • can monitor serum levels numerous times daily

- EKG with high infusion rates (>15 mmol/hr)

33
Q

Hypokalemia:

How do we monitor inpatient setting with mild-moderate acute deficiency ?

A

replace and check serum levels daily-every 3 days

34
Q

Hypokalemia:

Remember to check ____ levels if K+ replacement is not correcting serum levels

A

Mg++

35
Q

Hypokalemia:

In an ambulatory setting (ex. K+ supplementation with diuretic) how often do you monitor?

A

check serum level, renal function q1-2 months if levels have been stable

36
Q

Definition of hyperkalemia

A

serum K+ > 5 mmol/L

37
Q

Hyperkalemia due to ?

A

due to total body K+ surplus or extracellular shifting

38
Q

Symptoms of mildly elevated K+

A

usually asymptomatic

39
Q

Symptoms of moderately to severely elevated K+

A

EKG changes, arrhythmias, mortality

40
Q

What are 4 main causes of hyperkalemia?

A

1) Increased K+ intake
2) Decreased K+ excretion
3) Decreased effect of aldosterone
4) Extracellular movement of total body potassium (pseudohyperkalemia)

41
Q

Hyperkalemia:

Increased K+ intake usually a problem in ?

A

Severe renal impairment or dialysis:

  • Non-compliance with diet restrictions
  • Unwittingly using KCl salt substitutes
  • OTC/alternative products containing potassium ?
42
Q

Hyperkalemia:

Impaired excretion in renal failure alone or in conjunction with medications such as ??

A
  • ACEi
  • ARB
  • potassium sparing diuretic (spironolactone)
  • NSAIDs

Less common but notable:

  • digoxin
  • TMP-SMX
  • heparin

Caution with additive effects of >1 medications listed above

43
Q

Hyperkalemia:

What can cause falsely elevated serum K+ ?

A
  • Intracellular potassium can spill from RBCs
  • Lab will usually note if sample appears hemolyzed
  • Consider false elevation if other labs (blood CO2, renal function) normal
  • Redraw sample before making treatment decision
44
Q

Hyperkalemia:

Tx for mild hyperkalemia?

A

may self correct with monitoring, may or may not opt to treat

45
Q

Hyperkalemia:

What is Tx for hyperkalemia with EKG changes?

A

emergency, immediate Tx needed

46
Q

Hyperkalemia:

Aim therapies to either ??

A

a) Reduce total body stores of potassium

b) Correct extracellular (serum) levels by temporarily driving K+ intracellularly

47
Q

Hyperkalemia:

First stabilize cardiac membrane with ??

A

Cardiac membrane (reverse EKG changes) - IV calcium

  • acts within 5 minutes, lasts 30-60 minutes
  • DOES NOT CHANGE SERUM POTASSIUM LEVEL - need additional measures
48
Q

Hyperkalemia:

Because stabilizing cardiac membrane with IV calcium does not change serum potassium levels, you need additional measures: What are these additional measures?

A
  • Calcium gluconate 1 g IV or calcium chloride 1 g IV

- Calcium chloride has 3 times the elemental calcium, but caution with tissue necrosis

49
Q

Hyperkalemia:

After the calcium treatment, what is the next step?

A

Drive serum potassium intracellularly:

-Regular insulin 10 units IV x 1 (if not already hyperglycaemic, give dextrose 25 g IV x 1 concurrently to avoid hypoglycaemia)

and/or

-Beta-2 agonists - salbutamol 10 mg nebule inhaled x 1 (4x more than usual dosing for pulmonary indications)

50
Q

Hyperkalemia:

What is Tx for severe hyperkalemia caused by metabolic acidosis (decreased extracellular pH) ?

A

Can also give sodium bicarbonate 50-100mg IV x 1

  • Raises pH, potassium moves into cells and therefore decreases extracellular K+
  • Not a Tx of choice outside of metabolic acidosis patient
  • Doesn’t work as well in patients with end-stage renal disease
51
Q

Hyperkalemia:

How come you can’t give SC insulin for hyperkalemia ?

A

bc it has a longer duration of effect than dextrose and patient can become hypoglycemic

52
Q

Do we treat pseudohyperkalemia ?

A

treatment was not even required

53
Q

How do you treat mild hyperkalemia? (2 options)

A

1) Sodium polystyrene sulfonate (commonly known by brand name Kayexalate)
2) Furosemide

54
Q

Describe Kayexalate Tx for mild hyperkalemia

A
  • cation exchange resin
  • exchanges sodium for potassium 1:1 in intestine
  • takes many hours to see full effect
  • can give PO or PR, typically 15-45 grams per dose
  • contraindicated in bowel dysfunction
  • risk of colonic necrosis, linked more to sorbitol-containing formulations
  • may bind other medications - spacing medications 6 hours apart prudent
55
Q

Describe furosemide Tx for mild hyperkalemia

A

Furosemide - ex. 40 mg IV x 1, increase urinary potassium loss

  • onset of action within minutes
  • duration 4-6 hours
56
Q

How much sodium does human body require?

A

1.5 grams daily

57
Q

Sodium:

The predominant _____ cation

A

extracellular

58
Q

What is normal sodium serum concentration ?

A

135-147 mmol/L

59
Q

What lab value defines hyponatremia ?

A

serum sodium < 135 mmol/L

60
Q

What are the 3 categories of hyponatremia?

A

1) Hypovolemic hypotonic hyponatremia
- Common with thiazide diuretics

2) Euvolemic hyponatremia
- Associated with SIADH

3) Hypervolemic hyponatremia
- Associated with cirrhosis, heart failure, nephrotic syndrome

61
Q

Presentation of mild hyponatremia

A

usually asymptomatic, impairment of attention and gait, and increased fall risk possible

62
Q

Presentation of moderate hyponatremia

A

headache, lethargy, restlessness, disorientation

63
Q

Presentation of severe hyponatremia

A

seizures, coma, respiratory arrest, brain damage, death

64
Q

Describe the basics of hyponatremia Tx

A

-Treat the underlying cause to correct the level

65
Q

How do you treat hypovolemic hyponatremia ?

A

treat with IV NaCl (0.9% or sometimes 3% if severe)

66
Q

How do you treat euvolemic or hypoervolemic hyponatremia?

A

try fluid restriction first

67
Q

What can rapid swings in sodium levels cause?

A

Osmotic demyelination syndrome: damage to myelin sheath in the brainstem

68
Q

Rule of thumb for sodium correction (to prevent osmotic demyelination) ?

A

never increase serum Na+ level more than 12 mmol/L/24 hours (and more conservative than that if hyponatremia has been chronic)

Clinical 2 (Part B) (30 decks)

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