Potassium Balance

• Potassium concentration dramatically affects excitable membrane function (muscle and nerve)

• Symptoms: muscle weakness, nausea, lethargy, arrhythmias (both low and high potassium); EKG with peaked T waves (hyperkalemia) or ST segment depression and T wave inversion (hypokalemia)

• Renal potassium management is also dependent on Na/K/H+ exchange in the distal tubule

• Decreased potassium concentration = Hypokalemia
  1. Inadequate intake of potassium

  2. Treatment of normokalemic dehydration without potassium supplementation (dilutes potassium)

  3. Mineralocorticoid excess (Cushing's syndrome and hyperaldosteronism; increased Na/K/H exchange in the distal tubule)

  4. Renal loss of potassium associated with diuretic therapy

  5. GI loss (protracted vomiting or diarrhea)

  
  
  
  

• Increased potassium concentration = Hyperkalemia
  1. Dehydration

  2. Renal failure (decreased Na/K/H exchange in the distal tubule)

  3. Endocrine diseases with mineralocorticoid deficiency (decreased Na/K/H exchange in the distal tubule)

  4. "Potassium sparing" diuretics (e.g., spironolactone; inhibit water uptake in the distal tubule by inhibiting Na/K/H exchange)

  5. Tumor lysis (release of intracellular potassium)

  6. Artifactual hemolysis of blood specimens after drawing (release of intracellular potassium)