Definition – potassium < 3.5 mEq/L.

Cancellation of surgery – based on a low serum potassium is not generally warranted.

Heart affects – Decreases the cardiac depolarization threshold. Classic ECG signs of hypokalemia include a U wave and prolonged QT interval

Dysrhythmias – Hypokalemia is one of the major causes of perioperative dysrhythmias.  Lethal dysrhythmias (ie. ventricular fibrillation) warrant aggressive treatment (IV potassium 10-20 mEq/hr).  Treatment should ALWAYS be accompanied by ECG monitoring. If repletion of potassium is too fast, other lethal dysrhythmias may result – monitor closely.  Potassium repletion solutions WITHOUT glucose are preferred.

Not typically treated during CPB – this is due to the significant amount of potassium found in the cardioplegia solution.

May prolong neuromuscular blockade – in fact, hypokalemia interferes with reversal.  watch TOF closely

Digoxin toxicity – hypokalemia may enhance or induce digitalis and digoxin toxicity

B2 agonism (eg. terbutaline, albuterol) – stimulates the migration of extracellular potassium into the cell (out of the plasma – which reduces plasma potassium levels even further)

Signs and Symptoms are typically in the cardiac and neuromuscular systems:
tetany, muscle weakness, dysrhythmias, cramps, paralysis, ilius, prolonged QT interval (greater than 440 ms)

Anesthesia causes: respiratory alkalosis (hyperventilation), aggressive diuresis, gastric suctioning, insulin administration, short-acting bronchodilators (ie. albuterol)

Diseases: Hyperaldosteronism (Conn’s Disease), Bartter syndrome, Cushings syndrome, renal tubular defects, renal failure, liver disease, familial periodic paralysis

Pharmaceutical causes: Thiazide diuretics, loop diuretics, insulin, excessive corticosteroid therapy, Kayexalate, aminoglycosides, mannitol, amphotericin B, cisplatin, carbenicillin, β2 agonists, glucose irrigations, aldosterone antagonists, ritodrine

Other causes: licorice (glycyrrhizic acid), GI loss (diarrhea/vomiting), malnutrition (decreased intake/malabsorption), excessive sweating, burns, hyperglycemia, hypercalcemia, hypomagnesemia, metabolic alkalosis, respiratory alkalosis

Hypokalemia moves the resting membrane potential away from threshold – meaning it takes more to generate an action potential. This is why muscle weakness is often seen in patients with hypokalemia.