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DiBartola - Gautier > Chapter 5 - Disorders of Potassium > Flashcards

Chapter 5 - Disorders of Potassium Flashcards

1
Q

What is the major extracellular cation?

A

Na+

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2
Q

What is the major intracellular cation?

A

K+

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3
Q

What is the concentration of K+ in the intracellular fluid?

A

140mEq/L (variation in RBCs)

Muscle: 400 mEq/L

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4
Q

What is the concentration of Na+ in the intracellular fluid?

A

10mEq/L

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5
Q

As much as 95% or more of total body K is located within the cells. What area contains the most?

A

Muscle

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6
Q

What maintains the relationship between the ECF and ICF potassium concentrations?

A

Na/K ATPase

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7
Q

Na/K ATPase pumps ____ out of cells and ____ into cells.

A

Na, K

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8
Q

Na/K ATPase pumps in what ratio?

A

3Na/ 2K

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9
Q

A net _____ charge is within the cell and a net _______ charge is outside the cell.

A

Negative/ positive

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10
Q

What is the Nernst equation?

A

Resting cell membrane potential

Em = -61Log10 [Ki]/[Ko]

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11
Q

Hypokalemia ___________ the resting membrane potential

A

Increases/ makes more negative/ makes it less excitable

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12
Q

Membrane excitability is affected by potassium, but can also be affected by what two other things?

A

Calcium and acid-base balances

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13
Q

Ionized hypocalcemia _________ membrane excitability.

A

Increases (allows self perpetuating Na permeability to be reached with lesser degree of polarization)

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14
Q

Membrane excitability is ______ with alkalemia and ________ by acidemia.

A

Increased, decreased

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15
Q

T/F: Transport of K in the small intestine is active, while transport of K in the colon is passive.

A

False (passive in the small intestine and active in the colon)

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16
Q

Where is K removed from the body from?

A

Kidneys and GI tract

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17
Q

In dogs, what percent of K intake is eliminated via the kidneys?

A

90-98%

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18
Q

What 2 hormones promote cellular uptake of K in the liver and muscle by increasing the activity of Na/K ATPase?

A

Insulin and epinephrine

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19
Q

What type of acidosis is more likely to cause any clinically relevant change in serum K concentration during acute acid-base disturbances?

A

Mineral acidosis

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20
Q

T/F: Metabolic acidosis of at least 2-3 days duration is associated with increased urinary K excretion and mild hypoK.

A

True

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21
Q

What can help differentiate between renal and non-renal sources of potassium loss?

A

Fractional excretion of potassium

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22
Q

What are the common causes of hypokalemia / metabolic alkalosis, hypokalemia / metabolic acidosis, respectively?

A

Hypokalemia / metabolic alkalosis: vomiting of stomach contents, diuretic administration

Hypokalemia / metabolic acidosis: diarrhea caused by small intestinal disease, chronic renal failure, distal renal tubular acidosis

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23
Q

Causes of hypokalemia: Translocation (ECF to ICF)?

A 
alkalemia
insulin/glucose containing fluid
catecholamine
albuterol overdosage
hypothermia
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24
Q

Effects on muscle

  1. less than 3.0 mEq/L
  2. less than 2.5 mEq/L
  3. less than 2.0 mEq/L
A
  1. muscle weakness
  2. increased CK
  3. frank rhabdomyolysis
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25
Q

True/False: chronic hypokalemia leads to metabolic acidosis in both dogs and cats

A

True

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26
Q

True/False: hypokalemia renders the myocardium refractory to the effects of class 1 antiarrhythmic agents (lidocaine, quinidine, procainamide). Therefore, serum potassium concentration should be measured and hypokalemia should be corrected in dogs with ventricular arrhythmia unresponsive to antiarrhythmic therapy

A 
True
Lidocaine: class 1b
Quinidine: class 1a
Procainamide: class 1a
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27
Q

What are the main features of hypokalemic nephropathy?

A
  1. Renal vasoconstriction- decrease RBF and GFR

2. PU/PD from impaired responsiveness of the kidneys to ADH

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28
Q

Explain 3 categories of hypokalemia

A
  1. decreased intake
  2. translocation of K from ECF to ICF
  3. excessive loss of potassium by either the GI or urinary route
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29
Q

How much potassium is needed for maintenance fluid therapy?

A

15-30 mEq/L

30
Q

True/False: Rattlesnake envenomation is associated with hypokalemia

A

True. Mild hypokalemia was reported in 78% of dogs suffering from rattlesnake envenomation.

31
Q

What is the presumed mechanism of hypokalemia from beta2 adrenergic agonist overdose?

A

Rapid uptake of extracellular potassium by muscle and liver (stimulate Na-K pump embedded in the cell membrane)

32
Q

What breed of cat is reported to have familial disorder characterized by episodes of sudden translocation of potassium from ECF to ICF?

33
Q

T/F: hypokalemia is common in cats with CKD, whereas most dogs with CKD have normal serum potassium concentration

34
Q

What is the mechanism of hypokalemia induced by administration of loop or thiazide diuretics?

A

Blocks Na-Cl receptors in the distal convoluted tubule

  1. increased flow rate in distal tubule (decreased sodium reabsorption)
  2. increased secretion of aldosterone secondary to volume depletion (PUPD)
35
Q

What is the additive of choice for parenteral potassium supplementation and why?

A

KCl. Chloride repletion is essential if vomiting or diuretic administration is the underlying cause of hypokalemia.

36
Q

KCL should not be infused at rates greater than _____?

A

0.5 mEq/kg/hr

37
Q

What are the reasons for normo- or hyperkalemia in DKA cases?

A
  1. effects of insulin deficiency
  2. hyperosmolality on serum potassium concentration
  3. Hypovolemia
38
Q

In the proximal tubule, how is K reabsorbed?

A

Solvent drag via paracellular route

39
Q

In the thick ascending limb of the LoH, most K reabsorption happens by what route?

A

Paracellular

40
Q

T/F: The transepithelial electrical potential difference is lumen positive in the early proximal tubule.

A

False, the lumen is positive

41
Q

T/F: In the thick ascending limb of the LoH, the transepithelial electrical potential difference is lumen positive.

A

True, the lumen is strongly positive

42
Q

Transcellular reabsorption of K is facilitated by what in the luminal membrane?

A

Na-K-2Cl cotransporter

43
Q

Transcellular reabsorption of K is facilitated by what in the basolateral membrane?

A

K channels and and K-Cl cotransporters

44
Q

What cotransporter do thiazide diuretics inhibit?

A

Na-Cl cotransporter

45
Q

What cells in the connecting tubule and collecting duct are responsible for K secretion?

A

Principal cells

46
Q

Name 3 diuretics of the principal cells and what they work on.

A
  1. Amiloride- directly block electrogenic Na channel
  2. Triamterene- directly block electrogenic Na channel
    3, Spironolactone- antagonized aldosterone’s effect on the electrogenic Na channel
47
Q

Where are a-intercalated cells located?

A

Connecting tubule, CCD and outer medullary collecting duct

48
Q

Where are B-intercalated cells located?

A

Cortical collecting duct

49
Q

Where are the Cl-HCO3 countertransporters located in the a-intercalated cells?

A

Basolateral membrane

50
Q

What three main factors affect K secretion in the distal nephron?

A
  1. Magnitude of chemical concentration gradient for K between the tubular cells and tubular lumen
  2. Tubular flow rate
  3. Transmembrane potential difference across the luminal membranes of the tubular cells
51
Q

What is the most important hormone affecting urinary K excretion?

A

Aldosterone

52
Q

What two things directly stimulate the secretion of aldosterone?

A

Hyperkalemia

Angiotensin II

53
Q

What two things directly inhibit aldosterone release?

A

ANP

Dopamine

54
Q

What three things indirectly promote aldosterone secretion?

A

ACTH
Hyponatremia
Increased extracellular pH

55
Q

What is the primary effect of aldosterone?

A

Increase the number of open Na cells in the luminal membrane of principal cells

56
Q

T/F: Aldosterone increases the activity and number of Na-K ATPase pumps in the basolateral membrane of the principal cells.

57
Q

In what two ways does aldosterone influence H secretion?

A
  1. Directly promotes H secretion in H secreting type a-intercalated cells through stimulation of the H-ATPase present on the luminal membrane.
  2. Promotes H secretion in the distal tubule by stimulating electrogenic Na reabsorption in principal cells, increasing lumen negativity which favors enhanced H secretion
58
Q

T/F: Low Na intake is associated with decreased renal K excretion.

59
Q

T/F: Acute mineral metabolic alkalosis decreases urinary excretion of K.

A

False, it causes metabolic acidosis

60
Q

Chronic metabolic acidosis does what to urinary excretion of K?

A

Increases urinary excretion of K

61
Q

What is a normal K concentration in dogs and cats?

A

3.5-5.5mEq/L

62
Q

Why does serum K concentration exceed plasma concentrations?

A

Platelets release K during clotting

63
Q

T/F: There is a positive correlation between platelet count and serum K concentration in cats

A

False, the positive correlation is in dogs

64
Q

T/F: In normal adult canine and felines, hemolysis is not associated with hyperK.

65
Q

Which has higher K concentrations:

Neonatal dogs or adult dogs

66
Q

Which has higher K concentrations: Dogs with thrombocytopenia or thrombocytosis

A

Thrombocytosis

67
Q

Which has higher K concentrations: Canine red cells stored in citrate for 4 days or 40 days

68
Q

Which has higher concentations: Canine RBC or reticulocytes

A

Reticulocytes

69
Q

Which has higher K concentrations: Canine RBC with Na-K ATPase present or absent

70
Q

What breeds tend to have a high K phenotype for their RBC? (3 breed naturally, and 2 breed with a disease)

A

Naturally: Shibas, Akitas, Jindos
Disease: Phosphofructokinase deficiency- Springers and whippets

71
Q

Some dogs with the high K phenotype for their RBC can accumulate a lot of glutathione in their RBC. What food should they avoid?

A

Onions- they have a predisposition for oxidative damage

DiBartola - Gautier (11 decks)

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