19 - Electrolyte Disturbances Flashcards
What is the most common electrolyte imbalance?
hyponatremia
Total body stores of K+ is around ________ mmol
3000-4000 mmol
___% of K is intracellular
98
___% of K is extracellular
2
What is the ratio of Na and K in and out of cell?
3 Na+ out
2 K+ in
normal serum level of K+ ?
3.5-5 mmol/L
intracellular is 150 mmol/L
Elimination of K+ is usually ___% renally and __% GI
90% renally (secretion from distal tubules)
10% GI
What is potassium homeostasis affected by?
- Hormones
- Acid-base status
- Hyperosmolality
What hormones affect potassium homeostasis?
- insulin
- catecholamines
- aldosterone
How does insulin affect potassium homeostasis?
stimulates Na/K ATPase pump to transport K+ intracellularly
How does catecholamines (ex. epinephrine) affect potassium homeostasis?
Beta-receptor stimulation, which:
a) activates Na+/K+/ATPase pump, drives potassium intracellularly
b) causes glyconeogenesis - increases glucose - releases insulin, drives potassium intracellularly
How does aldosterone affect potassium homeostasis?
- acts at distal tubule
- increase urinary potassium excretion
*aldosterone antagonist cause K+ retention (ex. spironolactone - K+ sparing diuretic)
How does decreasing blood pH affect extracellular K+ ?
if pH decreases, extracellular k+ increases
How does increasing blood pH affect extracellular K+ ?
if pH increases, extracellular K+ decreases
How does hyperosmolality affect potassium ?
shifts to extracellular fluid
What is the definition lab value for hypokalemia?
K+ < 3.5 mmol/L
What is hypokalemia due to?
total body K+ deficit or intracellular shifting
What can moderately low hypokalemia cause?
-cramps, weakness, myalgias
What can severely low hypokalemia cause?
-EKG changes, arrhythmias, increased digoxin toxicity
What are the two common medication causes of hypokalemia?
- thiazides
- furosemide
What can hypokalemia also be caused by? (2 things)
1) Excessive GI loss
- diarrhea
- vomiting
- metabolic alkalosis can develop and decrease serum K+
* if pH goes up, extracellular K+ decreases
2) Hypomagnesemia
How can hypomagnesemia cause hypokalemia ?
- increases renal excretion of potassium
- important: need to correct underlying magnesium deficiency to correct
Non-pharms for hypokalemia treatment ?
- adequate dietary intake of potassium (yogurt and potatoes)
- potassium salt substitutes
What is pharmacological Tx for hypokalemia?
- Oral supplementation when mild, nausea/vomiting not a concern
- IV replacement for severe hypokalemia, vomiting
- replacement of magnesium first if hypomagnesemia (oral or IV)
What is the general rule of thumb for hypokalemia acute Tx?
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
Describe oral Tx for hypokalemia
- consider tablet vs liquid as tolerance can be an issue
- split doses to minimize GI irritation
Describe IV Tx for hypokalemia
- 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
What are some common oral replacement products for hypokalemia?
- 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)
For acute replacement for hypokalemia, how do we avoid GI irritation/nausea ?
- 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
For chronic replacement for hypokalemia (i.e. concurrent diuretic) how much oral replacement therapy can we give daily?
8-16 meq oral replacement therapy daily
If the hypokalemia is diuretic-induced, what can we add?
concurrent K+ sparing diuretic (ex. spironolactone)
Hypokalemia:
How do we monitor acute inpatient setting correcting severe hypokalemia?
- can monitor serum levels numerous times daily
- EKG with high infusion rates (>15 mmol/hr)
Hypokalemia:
How do we monitor inpatient setting with mild-moderate acute deficiency ?
replace and check serum levels daily-every 3 days
Hypokalemia:
Remember to check ____ levels if K+ replacement is not correcting serum levels
Mg++
Hypokalemia:
In an ambulatory setting (ex. K+ supplementation with diuretic) how often do you monitor?
check serum level, renal function q1-2 months if levels have been stable
Definition of hyperkalemia
serum K+ > 5 mmol/L
Hyperkalemia due to ?
due to total body K+ surplus or extracellular shifting
Symptoms of mildly elevated K+
usually asymptomatic
Symptoms of moderately to severely elevated K+
EKG changes, arrhythmias, mortality
What are 4 main causes of hyperkalemia?
1) Increased K+ intake
2) Decreased K+ excretion
3) Decreased effect of aldosterone
4) Extracellular movement of total body potassium (pseudohyperkalemia)
Hyperkalemia:
Increased K+ intake usually a problem in ?
Severe renal impairment or dialysis:
- Non-compliance with diet restrictions
- Unwittingly using KCl salt substitutes
- OTC/alternative products containing potassium ?
Hyperkalemia:
Impaired excretion in renal failure alone or in conjunction with medications such as ??
- ACEi
- ARB
- potassium sparing diuretic (spironolactone)
- NSAIDs
Less common but notable:
- digoxin
- TMP-SMX
- heparin
Caution with additive effects of >1 medications listed above
Hyperkalemia:
What can cause falsely elevated serum K+ ?
- 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
Hyperkalemia:
Tx for mild hyperkalemia?
may self correct with monitoring, may or may not opt to treat
Hyperkalemia:
What is Tx for hyperkalemia with EKG changes?
emergency, immediate Tx needed
Hyperkalemia:
Aim therapies to either ??
a) Reduce total body stores of potassium
b) Correct extracellular (serum) levels by temporarily driving K+ intracellularly
Hyperkalemia:
First stabilize cardiac membrane with ??
Cardiac membrane (reverse EKG changes) - IV calcium
- acts within 5 minutes, lasts 30-60 minutes
- DOES NOT CHANGE SERUM POTASSIUM LEVEL - need additional measures
Hyperkalemia:
Because stabilizing cardiac membrane with IV calcium does not change serum potassium levels, you need additional measures: What are these additional measures?
- Calcium gluconate 1 g IV or calcium chloride 1 g IV
- Calcium chloride has 3 times the elemental calcium, but caution with tissue necrosis
Hyperkalemia:
After the calcium treatment, what is the next step?
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)
Hyperkalemia:
What is Tx for severe hyperkalemia caused by metabolic acidosis (decreased extracellular pH) ?
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
Hyperkalemia:
How come you can’t give SC insulin for hyperkalemia ?
bc it has a longer duration of effect than dextrose and patient can become hypoglycemic
Do we treat pseudohyperkalemia ?
treatment was not even required
How do you treat mild hyperkalemia? (2 options)
1) Sodium polystyrene sulfonate (commonly known by brand name Kayexalate)
2) Furosemide
Describe Kayexalate Tx for mild hyperkalemia
- 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
Describe furosemide Tx for mild hyperkalemia
Furosemide - ex. 40 mg IV x 1, increase urinary potassium loss
- onset of action within minutes
- duration 4-6 hours
How much sodium does human body require?
1.5 grams daily
Sodium:
The predominant _____ cation
extracellular
What is normal sodium serum concentration ?
135-147 mmol/L
What lab value defines hyponatremia ?
serum sodium < 135 mmol/L
What are the 3 categories of hyponatremia?
1) Hypovolemic hypotonic hyponatremia
- Common with thiazide diuretics
2) Euvolemic hyponatremia
- Associated with SIADH
3) Hypervolemic hyponatremia
- Associated with cirrhosis, heart failure, nephrotic syndrome
Presentation of mild hyponatremia
usually asymptomatic, impairment of attention and gait, and increased fall risk possible
Presentation of moderate hyponatremia
headache, lethargy, restlessness, disorientation
Presentation of severe hyponatremia
seizures, coma, respiratory arrest, brain damage, death
Describe the basics of hyponatremia Tx
-Treat the underlying cause to correct the level
How do you treat hypovolemic hyponatremia ?
treat with IV NaCl (0.9% or sometimes 3% if severe)
How do you treat euvolemic or hypoervolemic hyponatremia?
try fluid restriction first
What can rapid swings in sodium levels cause?
Osmotic demyelination syndrome: damage to myelin sheath in the brainstem
Rule of thumb for sodium correction (to prevent osmotic demyelination) ?
never increase serum Na+ level more than 12 mmol/L/24 hours (and more conservative than that if hyponatremia has been chronic)
