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Background: Perioperative arrhythmia is a common general anesthesia complication of cardiothoracic surgeries. Sudden or acute onset of life threatening perioperative arrhythmias are rare clinical events in non-cardiac surgical patients. Electrolytes imbalance, particularly hypokalemia and dyskalemia, is one of the main possible underlining cause for the occurrence of these arrhythmias. We present two cases of severe hypokalemia leading to life threatening cardiac arrhythmias in the post-operative period. Case 1: A 30-year old healthy female patient without significant past medical history had emergency laparoscopic cholecystectomy and appendicectomy. Pre- and intraoperative periods were uneventful. Her pre-operative potassium level was 3.7 mmol/L. 18 hours post-operatively, she suddenly developed palpitations and went into ventricular fibrillation (VF) cardiac arrest. Cardiopulmonary resuscitation (CPR) was initiated followed by defibrillation which reverted the heart to a sinus rhythm. She was transferred to the intensive care unit (ICU) sedated and connected to the ventilator. In ICU, her serum electrolytes showed severe hypokalemia (serum potassium level 2.2 mmol/L) (Figure 1) so she was immediately started on 20 mmol of potassium chloride (KCl) over 30 minutes through central venous catheter (CVC) with complementary intravenous fluids with KCl. In the next 36 minutes she had four episodes of VF requiring CPR and defibrillation with a positive outcome. She received amiodarone infusion as well as continuous KCl supplementation and calcium gluconate 2 g. She received 100 mmol of KCl in 6 hours and a total of 220 mmol of KCl in 24 hours, and then she became stable. She was extubated after 48 hours. Echocardiogram and cardiac conduction studies showed no pathological changes. Cardiac conduction studies (electrophysiology study - EPS) were normal. She was discharged home and followed in the outpatient clinic. Case 2: A 78-year old known hypertensive male patient on angiotensin converting enzyme inhibitors was admitted to intensive care unit (ICU) for observation after laparoscopic cholecystectomy. Pre-operative serum electrolytes were within normal range. After one hour he started to have tachycardia and then went into pulseless ventricular tachycardia requiring defibrillation. His serum electrolytes results showed severe hypokalemia (2.4 mmol/L) (Figure 1) so this was corrected by rapid potassium chloride administration through CVC and supplementation of KCl in intravenous fluids. After 10 minutes he went into VF requiring defibrillation and a bolus of amiodarone. In the next 20 minutes he had three more episodes of VF requiring CPR and defibrillation. In six hours he required 90 mmol of KCl to reach a serum potassium level of 3.7 mmol/L. A total of 210 mmol of KCl was needed in 24 hours. He was extubated after 24 hours. He was transferred to the ward on day 3 and discharged home on day 6, and later followed in the outpatient clinic. Conclusion: Perioperative severe hypokalemia can lead to life threatening cardiac arrhythmias. Early recognition and aggressive correction through perioperative potassium supplementation is essential for better outcome. Daily potassium level assessment and supplementation should be done in the perioperative period. [ABSTRACT FROM AUTHOR]