Potassium

K+ 3.5 – 5.0 mEq/L                 Total K+ = 50 mEq/kg

  • 98% intracellular (75% is in muscle)
  • Disorders of potassium
    • Problems with K+ intake
      • Normally kidneys protect against hyperkalemia by extreting excess K+
    • Problems with distribution between IC and EC spaces
      • Transcellular shift – integrity of cell membrane, Na-K-ATPase activity, internal state of body ([K+], acid-base status, serum tonicity); rhabdomyolysis; insulin and beta 2-adrenergic catecholamines (increase Na-K-ATPase activity, drive K+ intracellularly); acidosis (H+ into cell and K+ out); alkalemia and hypertonicity i.e. hyperglycemia (K+ moves into cells)
      • 0.1 ∆ in pH = 0.6 ∆ in K+ (correct for pH)
    • Problems with K+ excretion
      • Amount of K+ excreted depends on
        • Plasma [K+] (if increased, stimulates nephron Na-K-ATPase – K+ moves into tubular lumen and excretion
        • Plasma aldosterone (K+ excretion)
        • Delivery of Na+ and H2O to DCT (if increased, stimulates Na-K-ATPase and increased tubular flow – K+ washout and elimination)



 

Hypokalemia

  • Symptoms
    • ↓↓↓ in extracellular K+ and ↓ in intracellular K+ → hyperpolarization of cell membrane and prolongation of AP and refractory periods (increased automaticity and excitability)
    • Cardiac: dysrhythmias, conduction defects
    • Skeletal muscle: weakness (LE affected more than UE, cranial muscles spared), paralysis, rhabdomyolysis, fasiculations and tetany
    • GI: ileus
    • Renal: nephrogenic DI, and metabolic alkalosis
    • EKG changes:
      • Increased P-wave amplitude
      • Prolonged PR interval
      • U waves
      • ST depression
      • Flat T-wav
  • Etiology
    • Inadequate intake (rare) – eating clay which binds K+
    • Transcellular shif
      • Medication induced:
        • Beta2 sympathomimetic agonists (increase Na+ into cells in exchange for H+ which stimulates Na-K-ATPase to drive Na+ out and K+ in) i.e. ventolin
        • Phosphodiesterase inhibitors (theophylline, caffeine)
        • Insulin
        • Barium poisoning
        • Verapamil overdose
        • Digoxin
      • Non-medication induced:
        • Metabolic and respiratory alkalosis (exchange EC K+ for IC H+)
        • Hypothermia
    • Excessive loss
      • Extra-renal (vomit, diarrhea, NG tube)
      • Renal – do a urine K+ (will be ↑)
        • Diuretics (thiazide and loop – ↑ Na+ and Cl to DCT)
        • Osmotic diuresis
        • Aldosterone (↑ open Na+ pores, ↑ Na-K-ATPase in nephron) – 10 or 20 hyperaldosteronism, Cushing’s, high dose steroids or ↑ renin
        • Cyclosporin
  • Treatment:
    • Determine cause and treat cause
    • Oral KCl – 20-80meq/d (safest)
    • Liquid KCl – 40-60meq/dose (rapid elevation – urgent, not emergent)
    • IV KCl – 20-40 meq/hr (severe symptoms)
    • Watch out for rebound hyperkalemia due to transcellular shift

Hyperkalemia

  • Symptoms
    • Cardiac – impaired conduction with risk of asystole or V fib.
    • Neuromuscular – cramps, weakness, paralysis, paresthesias, ↓DTR
    • GI
    • EKG changes
      • Tall peaked T-waves
      • Flat P-waves
      • Wide QRS comple
  • Etiologies
    • Pseudohyperkalemia (K+ released from cells at time of phlebotomy or after collection)
    • ↓ K+ excretion (↓ Na+ and H2O to DCT – RF or real/effective circulating volume depletion; ↓ effectiveness or concentration of aldosterone) – K+ sparing diuretic plus an ACEi (decreased aldosterone)
    • Increased K+ load
    • Transcellular shifting (insulin deficiency, rhabdomyolysis, tumor lysis syndrome, hemolysis, acidosis, hypertonicity, exercise, Drugs)
  • Treatment
    • Cardiac membrane stabilization (significant EKG abN)
      • Calcium gluconate 10mL of 10% soln, repeat once in 5-10min.
    • Reduce plasma K+ by transcelular shift
      • Insulin and glucose (10 units IV with 50 mL of 50% soln or 10 units in 500mL of D10W over 1 hour) – give the glucose first
      • Beta-2 agonists like albuterol – 10-20mg in 4 mL saline nebulized over 20min
    • Remove K+ from body
      • Kayexalate or sodium polystyrene sulfonate – exchange resin working across GI mucosa; 30g PO, 50g PR – takes ~1hour to work
      • Lasix or furosemide 20-40mg IV
      • Dialysis
    • Determine cause / prevent recurrence

Mild 5.0-6.5
Worry if >6.5
But also assess symptoms and ECG changes!!!!

Leave a Comment