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Potassium Homeostasis

  • Potassium Homeostasis
    • There is a substantial variation in the daily urinary excretion of K+. Hence, use caution in using Urinary K+ in the evaluation of hypo- or hyper-kalemia.
    • Time of the day also affects the adaptation to a potassium load.
    • Do not give potassium in a glucose solution while treating for hypokalemia
    • Plasma Potassium is a balance of 
      • 1. K+ Intake
      • 2. Internal Potassium homeostasis
      • 3. K+ Output (renal or extra-renal) 
    • Homeostasis: 2 concurrent process are involved
      • External Potassium Homeostasis i.e. (Renal K + excretion = K intake - (extra renal potassium loss + correction of potassium deficit) i.e  steps 1 and 3 from above
        • 3 control system
          • 2 Reactive system
            • Negative Feedback Loop i.e Dependent of potassium level
            • Feedforward Loop i.e Independent of potassium level
          • 1 Predictive system (circadian rhythm at suprachiasmic nucleus in brain) . It modulates the reactive system
      • Internal Potassium Homeostasis i.e distribution of potassium in body (98% intracellular, and 2% extracellular) i.e step 2 from above 
        • Case examples: 
    • Renal Regulation of Potassium
      • 400 or more meQ of K / day is handled by well functioning kidney
      • Filtered K is largely reabsorbed in PCT and LoH; Hence, K+ excreted in Urine is mainly a balance of K+ secretion and reabsorption in Cortical Distal Nephron and CD 
        • Potassium Secretion
          • Homeostatic
          • Contra-Homeostatic
        • Potassium Reabsorption
          • Homeostatic
          • Contra-homeostatic
    • Reference
  • HYPOKALEMIA: K: Low:  Check for Magnesium; Check potassium in Urine -- Is Kidney doing its work right? -- if not High BP or not -- i.e ? Hyper-aldosteronism or not -- Primary vs Secondary Hyperaldosteronism (see algorithm below)
    • Do EKG (only way to tell if hyperkalemia is life threatening or not)
    • Plasma K is more accurate than serum K
    • KCl: Only given via central line
    • KGluconate: Can be given through peripheral access

HYPERKALEMIA: K: High: Renal Failure? Acidosis (trans-cellular shift), Type 4 RTA, Drugs à EKG à Rx: Calcium Gluconate (If EKG Changes), Insulin, (regular IV 10 units) with 5% Dextrose; Bicarbonate; Beta-agonist Inhalation (K-BOMB); Resin (Kayexelate)