Beta Blocker Overdose

Beta blocker overdose causes bradycardia, hypotension and cardiogenic shock, with hypoglycemia in children. Severity depends on the agent. Propranolol is highly lipophilic and also blocks sodium channels, so it causes early coma, seizures and QRS widening. Sotalol blocks potassium channels, so it prolongs the QT interval and causes torsades de pointes. Atenolol, nadolol and sotalol are hydrophilic and renally cleared, so toxicity is prolonged in kidney failure.

Ingestion of more than 3 to 5 times the therapeutic dose is concerning. Symptoms start within 1 to 2 hours, and within 6 hours in most, but sustained-release products can delay deterioration for 12 to 24 hours. Coingestion with calcium channel blockers, digoxin or clonidine greatly raises mortality. Complications: refractory shock, asystole, seizures, pulmonary edema, bronchospasm in asthmatic patients, hyperkalemia and mesenteric ischemia.

• Dizziness, fatigue, nausea, vomiting
• Sinus bradycardia, atrioventricular block, junctional escape rhythm, hypotension, cool peripheries, heart failure
• Propranolol: drowsiness, coma and generalized seizures within 1 to 2 hours, QRS over 100 ms, ventricular tachycardia
• Sotalol: QT prolongation and torsades de pointes
• Hypoglycemia (children and fasting patients), hyperkalemia, bronchospasm
• Red flags: systolic pressure under 90 mmHg, heart rate under 50 beats a minute, QRS widening, seizures, depressed consciousness, and any coingestion of calcium channel blocker or digoxin

1. 12-lead ECG on arrival and repeated every hour: rate, PR, QRS and QTc.
2. Continuous cardiac monitoring for at least 6 hours (24 hours for sustained-release preparations and sotalol).
3. Capillary glucose hourly, and potassium, magnesium, calcium, creatinine, lactate and blood gases.
4. Echocardiography at the bedside to measure contractility and guide inotropes in shock.
5. Paracetamol and salicylate levels, and a coingestant screen.

Differentials: calcium channel blocker poisoning, digoxin toxicity, clonidine toxicity, organophosphate poisoning, primary conduction disease, myocardial infarction.

1. Airway and access: secure the airway for depressed consciousness, two IV lines, and IV crystalloid 10 mL/kg cautiously, since the heart may fail.
2. Decontamination: activated charcoal 50 g orally (children 1 g/kg, maximum 50 g) within 1 to 2 hours if the airway is protected. Whole bowel irrigation (polyethylene glycol 2 L/h orally or by tube, children 25 mL/kg/h) for large sustained-release ingestions.
3. Atropine: 0.5 to 1 mg IV every 3 to 5 minutes up to 3 mg (children 20 micrograms/kg, minimum 0.1 mg). Often ineffective.
4. Glucagon: 5 mg IV bolus over 1 to 2 minutes (children 50 micrograms/kg, maximum 5 mg), repeated up to 10 mg, then infusion 2 to 5 mg/h (children 50 micrograms/kg/h) titrated to response. Give ondansetron 4 to 8 mg IV first, since vomiting is expected.
5. Calcium: calcium chloride 10% 10 to 20 mL IV over 10 minutes (children 0.2 mL/kg), repeated every 10 to 20 minutes up to 3 doses, through a central line when possible.
6. High-dose insulin euglycemia therapy for shock:
   • Regular insulin 1 unit/kg IV bolus (with 25 g dextrose bolus if glucose is under 14 mmol/L).
   • Infusion 1 unit/kg/h, increased every 30 minutes by 1 unit/kg/h to a maximum of 10 units/kg/h until perfusion improves.
   • Dextrose 10% or 20% infusion at 0.5 g/kg/h titrated to glucose of 6 to 10 mmol/L, with glucose every 30 minutes initially, then hourly.
   • Keep potassium at 3.0 to 3.5 mmol/L (replace when under 2.5 mmol/L), and check magnesium and phosphate.
7. Vasopressors: norepinephrine 0.05 to 1 microgram/kg/min or epinephrine 0.05 to 1 microgram/kg/min.
8. Lipid emulsion 20% for propranolol or refractory shock: 1.5 mL/kg IV bolus over 1 minute then 0.25 mL/kg/min for 30 to 60 minutes (maximum 12 mL/kg).
9. QRS widening over 100 ms (propranolol): sodium bicarbonate 1 to 2 mmol/kg IV (1 to 2 mL/kg of 8.4%), repeated until the QRS narrows.
10. Sotalol: magnesium sulfate 2 g IV over 10 minutes (children 50 mg/kg, maximum 2 g), potassium to over 4.0 mmol/L, overdrive pacing at 100 to 120 beats a minute or isoprenaline 2 to 10 micrograms/min for torsades.
11. Seizures: lorazepam 4 mg IV (children 0.1 mg/kg, maximum 4 mg).
12. Refractory shock: transvenous pacing (capture is often poor), intra-aortic balloon pump and venoarterial extracorporeal membrane oxygenation.
13. Haemodialysis for atenolol, nadolol and sotalol in renal failure.

Observation for at least 6 hours for immediate-release and 24 hours for sustained-release products and sotalol. Psychiatric assessment before discharge.