Diseases of Potassium Regulation

Question 1

Factors that regulate intracellular potassium

Answer 1

• insluin
  
  • ==> i_ncreased 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

Question 2

Factors that regulate ECF potassium

Answer 2

• 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

Question 3

Causes of low serum potassium

Answer 3

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

Question 4

Acute causes of hypokalemia

Answer 4

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

Question 5

Chronic causes of hypokalemia

Answer 5

• 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

Question 6

Physiologic impact of hypokalemia

Answer 6

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

Question 7

Treatment of hypokalemia

Answer 7

• 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

Question 8

Physiologic effects of hyperkalemia

Answer 8

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

Question 9

DDx for low TB K⁺ w/metabolic alkalosis

Answer 9

• 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

Question 10

Types of hyperkalemia

Answer 10

• 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

Question 11

Causes of high TB K⁺(chronic hyperkalemia)

Answer 11

• 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

Question 12

Causes of transcellular shift (acute hyperkalemia)

Answer 12

• 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

Question 13

Tx of hyperkalemia

Answer 13

• 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+)