Potassium: Hyperkalemia and Hypokalemia

Question 1

Where is most of the K in our body?

Answer 1

98% is intracellular

Question 2

What is the intracellular K concentration and what is the extracellular K concentration?

Answer 2

intracellular = 140 mM

extracellular -= 4 mM

Question 3

A decrease of K by 1 mM reflects what in total body?

Answer 3

a 200-400 meq total body deficit - huge!

Question 4

What are the main symptoms of low and high K+ and how does this relate to K;s function in the cell?

Answer 4

they relate to an inability to generate action potentials in the muscles - muscle weakness/paralysis starting in the legs, along with EKG changes and cardiac arrhythmias

Question 5

What are the EKG changes in hypokalemia?

Answer 5

PR interval prolongation
ST depression
Flattened or inverted T waves
U waves
QRS widening

Question 6

What are the EKG changes in hyperkalemia?

Answer 6

PR interval prolongation
Elevated T waves
Widened QRS interval

Question 7

What protects against hyperkalemia: hypercalcemia or hypocalcamie?

Answer 7

hypercalcemia - it increases threshold potential and protects against hyperkalemia (which has a decreased resting potential)

Question 8

Is hyperkalemia exacerbated by metabolic acidosis or alkalosis?

Answer 8

acidosis - K+ is released from cells as HCl is buffered into cells

Question 9

Which is tolerated better - chronic or acute hyper/hypokalemia?

Answer 9

chronic

Question 10

What is potassium’s relationship with digoxin?

Answer 10

a bad one…

digoxin toxicity is worse with hypokalemia, but digoxin can cause hyperkalemia

Question 11

The risk of hyperkalmia is potentiated by hyponatremia or hypernatremia?

Answer 11

hyponatremia - less action of the Na/K ATPase

Question 12

What are the three conditions/states that influence the distribution of K_ between cells and the extracellular fluid?

Answer 12

1. concentration of K
2. acid-base status
3. insulin/catecholamine presence - they’ll move K into the cells

Question 13

HOw is K excreted?

Answer 13

almost entirely by the kidneys

Question 14

There’s a butt load of K in a glass of OJ. Why don’t we keep over during breakfast?

Answer 14

Because K+ will rapidly distribute into the cells because of catecholamine and insulin release and the newly high K concentration - this brings the extracellular K concentration back to normal very quickly

Question 15

How do insulin and catecholamines get K into the cells?

Answer 15

they upregulate the Na/K ATPase

Question 16

What direction will K move in acidemia? alkalosis?

Answer 16

acidosis = K will move out of the cells as H is buffered into cells (hyperkalemia)
alkalosis = K will move into cells as H is buffered into the extracellular fluid (hypokalemia)

Question 17

What are hte major controls on K secretion by the kidneys?

Answer 17

1. plasma K concentration = more K, more secretion
2. urin flow in distal tubule = more flow, more secretion
3. aldosterone = released during times of hyperkalemia to cause K secretion by principal cells of collecting tubule

Question 18

In general, describe K handling by the renal tubule?

Answer 18

1. filtered at glomerulus
2. reabosrbed in proximal tubule, following water and sodium
3. reabsorbed in LOH via NaK2Cl carrier
4. Secreted in distal tubule and collecting tubule via principal cells
5. can be reabsorbed in collecting duct by beta intercalated cells during severe hypokalemia

Question 19

What are the main causes of hypokalemia?

Answer 19

decreased intake (rare)
increaesd entry to cells
GI losses
increased urinary losses
increased sweat losses
dialysis

Question 20

What are some ways to get hypokalemia fro inadequate diet?

Answer 20

poverty - no fruits and veggies
exacerbated by diuretics
clay ingestion

Question 21

What are three ways to have hypokalemia from an increased K entry into cells?

Answer 21

metabolic alkalosis
hyperinsulinemia
increased catecholamines/beta agonists

Question 22

What are some ways you can get hypokalemia due to increased GI losses?

Answer 22

1. nasea/vomiting
2. nasogastric tube suction
3. diarrhea/intestinal fistulas

Question 23

How can you get kypokalemia due to increased urinary losses?

Answer 23

1. increased distal flow with impaired salt and water reabsorption from diuretics, salt wasting or polydipsia
2. hypercalcemia (increased distal flow)
3. mineralcorticoid excess - aldosterone mediated secretion
4. hypomagnesemia (affects K channels)

Question 24

What lab can you do to determine if K loss is from the GI tract or renal?

Answer 24

do a 24-hr urine K

the kidneys can decrease urine excretion ot K to 25-30 meg in 24 hours if the patient is hypokealmic.

if the urine K is appropriately low, the loss is somehwere other than th ekidney

Question 25

If you have low urinary K and acidosis, where is the loss? How about low urinary K and alkalosis?

Answer 25

acidosis = lower GI loss (laxatives, villous adenoma)

alkalosis = upper GI loss (vomiting)

Question 26

What are the complications of hypokalemia?

Answer 26

muscle weakness, cramps, cardiac arrhythmias

rhabdomyolysis

renal dysfunciton

hypertension (low K causes uptake of Na)

Question 27

What is the treatment for hypokalemia?

Answer 27

replace to get them out of danger initialy and then more gradually replace entire K deficit (either orally or IV)

treat underlying cause

Question 28

What are the general causes of hyperkalemia?

Answer 28

1. increased intake
2. shifting from inside cells to extracellular fluid
3. decreased urinary excretion

Question 29

What are some things that can cause the K to shift from the cells to the extracellular compartment?

Answer 29

muscle/tissue breakdown
insulin deficiency with hyperglycemia
metabolic acidosis

Question 30

What is the most common cause of hyperkalemia?

Answer 30

renal failure

Question 31

What effect will hypoaldosteronism have on K?

Answer 31

you’ll get hyperkalemia.

can be a syndrome, can be from drugs like ACEI or NSAIDS, can be from aldosterone resistance like with the K sparing diuretics, etc.

Question 32

How do you determine whether you should treat a hyperkalemia?

Answer 32

check for EKG changes

if K is 6.5 to 7 meq/l and EKG shows no changes, check for pseudohyperkalemia

If EKG changes - treat immediately

Question 33

How do you treat hyperkalemia?

Answer 33

1. antagonist K effects with calcium IV
2. shift K into the cells with glucose, insulin, bicarb and beta agonists. Give 3% NaCl is hyponatremia still present
3. remove excess K in the long run with diuretics, kayexalate and hemodialysis as last resort