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.
