Beta Blockers

Background

  • BB’s competitively block the binding of catecholamines at beta-adrenergic receptors resulting in decreased inotropy and chronotropy
  • Lipophilic BB’s (propranolol, metoprolol) cross the blood brain barrier and cause CNS depression. Membrane stabilizing BB’s (propranolol) can result in QRS prolongation, dysrhythmias, and seizures
  • Sotalol also has potassium channel blocking properties which can cause QTc prolongation and dysrhythmias. Blood glucose can be low as BB’s impair gluconeogenesis and glycogenolysis
  • The antidote is glucagon which stimulates adenyl cyclase increasing cAMP and increases the heart rate and blood pressure.

 

Evaluation

  • Physical Exam: CNS depression
  • Laboratory abnormalities:  Hypoglycemia or normoglycemia
  • ECG: Sinus bradycardia but also low degree AV block (i.e. 1st degree).

 

Management

  • IVF, calcium, vasopressors, glucagon
  • Intralipid infusion if refractory HoTN or pt codes from a lipophilic BB (i.e. Propranolol)
  • Glucagon must be given as IV bolus over 10 min (if you give faster, patients will vomit)
  • Epinephrine or Norepinephrine should be first line vasopressors. VA-ECMO should be considered as a last resort after medical therapy has failed. Hemodialysis is recommended for significant sotalol toxicity.

 

Quick dosing reference: if patient is hypotensive and bradycardic:

  • Glucagon: 10 mg over 10 min (vomiting occurs if administered too fast; max 10 mg/hr)
    • Infusion 3-5 mg/h (need infusion as half-life is 6 minutes)
  • Vasopressors: Norepinephrine (0.01 to 3 mcg/kg/min – adjust rate per ICU protocol)  or epinephrine (0.05 to 2 mcg/kg/min – adjust rate per ICU protocol)
  • Calcium: 3g calcium gluconate
  • Intralipid infusions for propanolol (1 liter over 1 hour) for refractory hypotension or if patient codes. Other dosing is 1.5 cc/kg bolus followed by 0.25 cc/kg/min over 60 min but for a 70 kg adult, this equates to 1 liter over 1 hour).