Hypokalemia is a topic covered in the 5-Minute Emergency Consult.

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Basics

Description

  • Defined as a serum potassium level <3.5 mEq/L:
    • Mild: 3–3.5 mEq/L
    • Moderate: 2.5–3 mEq/L
    • Severe: <2.5 mEq/L
  • Frequency:
    • Up to 20% of inpatients have documented hypokalemia (5% have levels <3 mEq/L).
    • Up to 14% of outpatients are mildly hypokalemic (most are related to diuretics or GI loss).
    • 5% of geriatric patients have K <3 mEq/L.
  • Potassium is the major intracellular cation:
    • Gradient is maintained by Na–K ATPase activity (enhanced by insulin and β-agonists) and mineralocorticoids.
  • Total body potassium is ∼55 mEq/kg of body weight (98% ICF, 2% ECF).
  • Electrophysiologic effects of hypokalemia:
    • Increase in the normal intracellular to extracellular potassium gradient:
      • Alters the depolarization threshold for muscles and nerves
      • Inhibits the termination of action potentials
    • Alterations in intracellular potassium directly affect cellular function.

Etiology

Renal Losses
  • Diuretics (thiazides, loop diuretics, carbonic anhydrase inhibitors), usually associated with loss of other cations (Mg2+, Ca2+, P3+, Na+)
  • Renal tubular damage:
    • Primary renal tubular disorders (RTA type I and II)
    • Interstitial nephritis, analgesic nephropathy, drug toxicity (amphotericin, gentamicin, toluene, cisplatin), myeloma kidney
    • Overdose toxicity: Acetaminophen, NSAIDs, hydroxychloroquine
  • Hyperaldosteronism:
    • Primary (primary hyperaldosteronism, Cushing, pituitary tumor-producing ACTH, congenital adrenal hyperplasia)
    • Secondary (volume depletion, CHF, cirrhosis, nephrotic)
    • Exogenous (steroids; fludrocortisone, glycyrrhizic acid [licorice]) hyperrenin state in renal artery stenosis
  • Hypomagnesemia (increased secretion)
  • Polyuria:
    • Osmotic diuresis (mannitol, hyperglycemia)
    • Psychogenic polydipsia
  • Congenital disorders:
    • Bartter and Gitelman syndromes—hypokalemic metabolic alkalosis and low BP
    • Liddle syndrome is the same but with hypertension.
  • Delivery of nonreabsorbable anions such that sodium is reabsorbed and potassium is exchanged out and excreted:
    • Bicarbonate in metabolic alkalosis
    • β-hydroxybutyrate in DKA
    • Hippurate in toluene abuse
    • Penicillins—high dose IV therapy

GI Losses
  • Diarrhea:
    • Proportional to volume and duration
    • Villous adenomas
    • Laxative abuse
  • Vomiting and nasogastric suction result in volume depletion and metabolic alkalosis, which increases renal losses of potassium from bicarbonaturia and hyperaldosteronism.
  • Ureterosigmoidostomy
  • Intestinal fistulae, ileostomy
  • Cystic fibrosis

Intracellular Shift of Potassium
  • Alkalosis (metabolic or respiratory)
  • Insulin:
    • Insulin administration
    • Stimulation of insulin release by IV glucose or massive sweetened beverage intake
    • Refeeding in prolonged starvation
  • Adrenergic excess:
    • Severe stress (trauma, MI, sepsis)
    • Treatment of asthma (frequent β-agonists and theophylline toxicity)
    • Cocaine, amphetamines, caffeine excess
    • Dobutamine, dopamine, pseudoephedrine
  • Hypokalemic periodic paralysis:
    • Familial
    • Thyrotoxic
  • B12 administration in severely deficient patient
  • Hypothermia
  • Drugs: GM-CSF, quetiapine, risperidone

Poor Intake (Rare as a Sole Cause)
  • Nutritional (poverty, pica, dementia)
  • Eating disorders
  • Dental problems/oral lesions
  • Esophageal disease

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Citation

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TY - ELEC T1 - Hypokalemia ID - 307440 Y1 - 2016 PB - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307440/all/Hypokalemia ER -