Diseases of Potassium Regulation Flashcards Preview

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Flashcards in Diseases of Potassium Regulation Deck (13)
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1

Factors that regulate intracellular potassium

  • insluin
    • ==> increased flux of K+ into cells
    • increased ECF [K+] ==> insulin release from pancreas
    • ==> stimulates Na/K ATPase + activates Na/H antiporter
  • catecholamines
    • ß2 adrenergic mediates K+ movement into cells
    • nonselective ß-block (propanalol) = inhibit K+ movement into cells
    • selective ß-block (metaprolol) = no impact

2

Factors that regulate ECF potassium

  • GFR has little role unless very low
  • Collecting tubule/fine-tuning segments
    • ENaC = exchanges Na and K + various K channels (passive)
    • aldosterone ==> upregulation of ENaC channel, K channels, and Na/K ATPase ==> increased K+ secretion + increased Na+ reabsorption

3

Causes of low serum potassium

  • spurious (high WBC)
  • decreased total body K+
    • decreased intake
    • increased loss: GI, renal
  • transcellular shift (stress)

4

Acute causes of hypokalemia

  • catecholamine excess (ß2 adrenergic)
    • Rx = ß2AR agonists (albuterol)
    • physio = stress ==> catecholamine release
  • insulin excess (rare)

5

Chronic causes of hypokalemia

  • Renal loss
    • urine [K+] > 20 mEq/L
    • metabolic acidosis = renal tubular acidosis or DKA
    • metabolic alkalosis = hyperaldosteronism
    • normal pH = magnesium depletion
  • Extrarenal loss = decreased intake or GI loss
    • urine [K+] < 20 mEq/L

    • metabolic acidosis=GI loss e.g. diarrhea

    • inadequate intake

6

Physiologic impact of hypokalemia

  • neuromuscular
    • weakness ==> paralysis @ extremities or chest wall (respiratory arrest)
  • cardiac
    • ECG abnormalities
    • unpredictable course

7

Treatment of hypokalemia

  • reverse correctable causes
    • stop diuretics, treat diarrhea, correct Mg deficiency 
  • asymptomatic
    • metabolic acidosis = K+ citrate or K+ bicarbonate
    • normal pH/metabolic alkalosis
      • normal BP = KCl; volume replace
      • high BP = K+-sparing diuretic
  • symptomatic ==> IV K+ replacement up to 40 mEq/hour
    • + ECG monitor 
    • + serum K+ monitoring

8

Physiologic effects of hyperkalemia

  • Neuromuscular
    • weakness
  • Cardiac
    • ECG changes = peaked T waves, absent P waves
    • 2nd/3rd degree heart block
    • potentially lethal

9

DDx for low TB K+ w/metabolic alkalosis

  • high urine chloride (>20 mEq/L)
    • Low BP = Bartter's Syndrome or Gittelman's Syndrome
    • High BP = Primary hyperaldosteronism or Cushing's Syndrome
  • low urine chloride (< 20 mEq/L)
    • diuretics

10

Types of hyperkalemia

  • spuriuos 
    • pseudohyperkalemia/artifiact due to: hemolysis, "tough draw", extended tourniquet time, high platelet count
  • high total body K+ (decreased renal K+ excretion) = chronic
  • Transcellular shift = acute

11

Causes of high TB K(chronic hyperkalemia)

  • GFR < 20 ml/min
    • GFR is the main problem when very low
    • exogenous K
    • endogenous K
    • medication
  • GFR > 20ml/min
    • Aldosterone high
      • Low urine Na = decreased Na delivery
      • High urine Na = drugs, PHA (pseudohyperaldo)
    • Aldosterone low 
      • Low renin = diabetes
      • high renin = adrenal insufficiency

12

Causes of transcellular shift (acute hyperkalemia)

  • Diabetes
    • No insulin + high blood glucose creates an osmotic driving force on water to leave cells and enter the ECF and K+ follows the water from cells to serum
  • Medications
    • Non-selective beta blockers block the B2 receptor from mediating K+ uptake into the cell
  • Ischemia or tissue damage
    • Rhabdomyolysis
    • Intestinal or peripheral vascular arterial insufficiency 

13

Tx of hyperkalemia

  • ALWAYS ECG first ==> tx if abnormal; continue w/work up if normal
  • Calcium gluconate = stabilizes cardiac arrhythmia
  • Sodium bicarbonate moves K+ into cells
  • Insulin +/- glucose
  • Albuterol nebulizer
  • K+ exchange resin (lowers total body K+)
  • Hemodialysis (lowers total body K+)