Disorders of K Metabolism

Question 1

Plasma K+ rises with ________ and falls with _______
(name that blood pH state)
↓↑→

Answer 1

acidemia, alkalemia

• in acidemia, K+ moves from ICF → ECF
• alkalemia increases K+ secretion

Question 2

Effects of alkalosis on K+ secretion

Answer 2

1. High pH causes movement of K+ into the all the cells from ECF
2. enhances electrochemical gradient for K+ secretion
3. Hypokalemic state

*note that alkalosis lowers H+ state, thus relieving their inhibitory effect on apical K channels→ faster flow of K+ into tubules

Question 3

Difference between mild and severe acidosis on K+ secretion

Answer 3

Acidosis should normally ↓ K+ secretion due to:

• inhibiting apical K+ channels
• stimulate K+ movement from the cells into ECF (away from lumen)

Severe acidosis should normally ↑ K+ secretion due to:
- inhibiting Na+ R → inhibiting H2O R → increasing tubular flow → ↑ K+ secretion

Question 4

Major determinants of urinary K+ excretion

Answer 4

1. Normal distal tubule function
2. Aldosterone activity
3. Urinary flow rate
4. Delivery of non-reabsorbed anions to distal nephron

Question 5

Aldosterone stimulates the distal part of the nephron, stimulating K+ secretion or reabsorption?

Answer 5

aldosterone stimulates the distal nephron secretion of K+
(it upregulates Na reabsorption→ K into the cell → K+ out of the cell)

*absence of aldosterone increases body K and plasma K, which in turn increases aldosterone secretion

Question 6

Increase in urinary flow rate does what to K+ excretion?

Answer 6

it should increase K+ excretion, by creating a favorable electrochemical gradient for tubular secretion

Question 7

Delivery of non-reabsorbed anions to distal nephron does what to K+ excretion?

Answer 7

It should increase.

Anions should “drag” K+ along as an obligate cation.

Question 8

Compare suddenly giving K+ to individuals who are maintained on a strictly low/moderate K+ intake vs giving low K+ diet with supplemental K+ .on the side

Answer 8

Low K+ diet + suddenly given K+ = severe hyperkalemia

Low K+ diet w/ supplemental K+ suddenly given K+ = harmless bc animal has adapted to high K+ loads and secrete K+ faster

Question 9

why is hyperkalemia a problem in acute renal failure but not usually in chronic renal failure?

Answer 9

K+ adaptation, in contrast to Na+ reabsorption is a slow process to turn on/off.
Hyperkalemia is a bigger problem in ARF than CRF unless GFR is extremly depressed.

Question 10

3 ways to evaluate ↓ Serum K+

Answer 10

Is the cause of low Serum K+ due to:

1. Spurious (fake) causes
2. Decreased TB K+
3. Transcellular shift

Question 11

Spurious(fake) causes of ↓ Serum K+

Answer 11

Extreme Leukocytosis WBC >100k

note that massively increased WBC also can lead to pseudohyperkalemia

Question 12

Decreased TB K+ leading to ↓ Serum K+ are due to which 2 things?

Answer 12

Renal 101:

1. decreased K+ intake
2. increased K+ loss
   - Renal or extrarenally

Question 13

Transcellular shifts leading to ↓ Serum K+ (5)

Answer 13

1. alkalosis
2. insulin excess (acute)
3. B2 adrenergic agonist excess (acute)
4. Hypokalemic periodic paralysis
5. Hypothermia

Question 14

Treatment of hypokalemia/K+ deficiency

Answer 14

Restore plasma and TB K+ to normal:

• intravenously during emergency (cardiac arrythmia or paralysis)
• orally
• diuretics that are K+ sparing (spirinolactone, triamterone, amiloride)

(very limited, scary to treat, bc you have to do these slow)

Question 15

Consequences of Hypokalemia/K+ deficiency

Answer 15

1. Metabolic
2. cardiovascular effects
3. Neuromuscular effects
4. Renal effects

Question 16

Metabolic effects of Hypokalemia

Answer 16

1. suppresses insulin release → glucose intolerance (high)
2. retards growth
3. intracellular acidosis
4. increase renal ammonia production → make it worse

Question 17

what do you have to worry about in pts on digitalis?

Answer 17

hypokalemia can enhance development of atrial/ventricular arrythmias in pts on digitalis

Question 18

Both hyper and hypokalemia have which neuromuscular effects?

Answer 18

muscle weakness

paralysis

Question 19

renal effects of hypokalemia

Answer 19

increased thirst

renal concentration defect → polyuria

Question 20

Hyperkalemia progression on EKG

Answer 20

if pt has >6.0, do an EKG

peaked T waves → Wide QRS complex w. flattened P waves → sine waves (more severe)

Question 21

EKG of hypokalemia

Answer 21

u waves after repolarization of T waves → artia/ventricular arrythmias in pts on digitalis

Question 22

Types of hyperkalemia and their causes

Answer 22

1. pseudohyperkalemia (spurious)
   - hemolysis of drawn blood (tight torniquet)
   - massively incrased WBC
2. True hyperkalemia
   - transcellular shift from ICF to ECF
   - decreased excretion
   - increased input

Question 23

Causes of transcellular shifts that result in true hyperkalemia (5)

Answer 23

reversible shift from ICF to ECF

• acidosis
• digitalis intoxication
• beta adrenergic blocker
• alpha 2 adrenergic agonist
• hyperglycemia!/hyperosmolar

Question 24

Causes of decreased excretion that result in true hyperkalemia

Answer 24

Acute renal failure
K+ sparing diuretics
hypoaldosteronism (low adrenal steroids)

Question 25

Causes of increased input that result in true hyperkalemia

Answer 25

endogenous ( hemolysis, rhabdo)
exogenous (K+ rich foods >300 mEq/d)
(note that diabetes/inadequate insulin response can also cause acute hyperkalemia) - acute

Question 26

Treatment of Hyperkalemia with ECG changes present

Answer 26

1. reverse the depolarization - stabilize membrane
   - calcium infusion
2. move K+ from ECF to ICF:
   - Sodium Bicarb
   - Glucose/insulin
   - beta agonist
3. remove K+ from body
   - diuretics
   - hemodialysis

Question 27

insulin deficiency, acidosis, beta blockers may result in hyper or hypokalemia?

Answer 27

hyperkalemia

-

Question 28

Vomiting, diarrhea, and anorexia could result in hyper or hypokalemia?

Answer 28

Hypokalemia (met acidosis)

- extrarenal cause

Question 29

How does K+ affect insulin?

Answer 29

K+ is a stimulus for insulin secretion

- insulin moves K+ from ECF to ICF

Question 30

What 3 hormones regulate internal K+ balance?

Answer 30

1. insulin
2. catecholamines
3. aldosterone

Question 31

How do catecholamines regulate K+

Answer 31

it moves K+ from ECF to ICF (just like insulin does), especially during stress via B2 receptor

Question 32

what plays key roles in regulating external K+ balance (very imp)

Answer 32

1. Kidney (reabsorption + SECRETION (unlike Na, water, ca, where there are just R)
2. Cortical collecting tubule
3. GFR (minor player)

Question 33

Chronic hypokalemia what should you assess? What do you expect to find?

Answer 33

Look at urine K+

- low (40 Meq/L) - renal

Question 34

low urine K

could be due to what?

Answer 34

Met acidosis
- diarrhea (GI losses)
Low K+ intake

Question 35

high Urine K (>40 Meq/L) - renal causes of hypokalemia

Answer 35

look at that cortical collecting duct K secretion

no acid base disorder: Mg depletion
metabolic alkalosis: aldosterone drives K+ and H+ secretion
metabolic acidosis: DKA

Question 36

What is the first test you would order in a pt with hyperkalemia?

Answer 36

repeat ECG

• if normal: work up first, treat second
• if not normal: treat now, work up second

Question 37

Low aldosterone would cause hyper or Hypokalemia?

Answer 37

Hyper: leads to less Na+ R and thus less K+ excretion