Hypotension and Bradycardia in the Poisoned Patient: Beta-Adrenergic Antagonists

As you recall, we are discussing the case of a 23 year old female with an intentional, unknown overdose and subsequent hypotension and bradycardia. We had a brief discussion of the differential and are now going to discuss specific management of the most important poisonings in our differential. The first category we will discuss is beta adrenergic antagonists (beta blockers).

Beta-Adrenergic Antagonists

Although beta blocker (BB) overdoses are often asymptomatic in healthy patients, severe toxicity can occur. The beta blocker poisoned patient will be hypotensive and bradycardic, and the ECG may show sinus bradycardia, an AV node block, sinus pauses, or, in severe cases, asystole. Acute congestive heart failure may be seen. Hypoglycemia is sometimes seen in children but is uncommon in adults. Propranolol overdose may cause respiratory depression and CNS symptoms such as seizures or coma; these are usually not seen in less lipophilic drugs such as atenolol. Sotalol is unique in that it often causes delayed toxicity and may present with prolonged QTc and ventricular tachydysrhythmias. Bronchospasm and significant potassium derangements are rare even in severely symptomatic poisonings although some degree of hyperkalemia may occur.

GI decontamination is indicated for any significant symptomatic ingestion of beta blockers. Activated charcoal, gastric lavage, or whole bowel irrigation should be considered, especially with a large ingestion of sustained release preparations. Glucagon should be given but may cause severe vomiting and aspiration and only improves blood pressure about 50% of the time. The starting dose is 3-5 mg IV and may be increased to 10 mg. An infusion can be started at 2-10 mg/hour if there is clinical response to the initial dose, but patients develop rapid tachyphylaxis and additional therapy may still be needed despite initial response. Calcium is effective at improving blood pressure even in isolated BB overdose and should be given. High-dose insulin should be initiated in hypotensive patients who do not improve with supportive care. Insulin should be given at 0.5-2 units/kg/hour with an initial bolus of 1 unit/kg/hour. Unless there is pre-existing hyperglycemia, 0.5 g/kg of dextrose should be given and a continuous dextrose infusion should be started to maintain euglycemia. Frequent monitoring of glucose and potassium is required. Lower doses of insulin do not appear to be effective and should not be used despite nursing staff reluctance to give insulin at much higher doses than they are accustomed to. A delay in clinical response of up to 60 minutes after insulin is initiated should be expected; vasopressors may be started concurrently with insulin or in patients who remain hypotensive despite insulin infusion. Intravenous lipid emulsion may be beneficial and should be given in the standard dosage used for local anesthetic poisoning.

In patients with refractory hypotension despite treatment, extracorporeal membrane oxygenation (ECMO) or intra-aortic balloon pump placement is reasonable if available, as most patients will survive if they can be supported until the toxic substance is metabolized.

Reference:
Brubacher JR. Chapter 61. β-Adrenergic Antagonists. In: Nelson LS, Lewin NA, Howland M, Hoffman RS, Goldfrank LR, Flomenbaum NE. eds. Goldfrank’s Toxicologic Emergencies, 9e . New York, NY: McGraw-Hill; 2011. http://accessemergencymedicine.mhmedical.com/content.aspx?bookid=454&Sectionid=40199456. Accessed December 1, 2014.

Howland M. Antidotes in Depth (A19): Glucagon. In: Nelson LS, Lewin NA, Howland M, Hoffman RS, Goldfrank LR, Flomenbaum NE. eds. Goldfrank’s Toxicologic Emergencies, 9e . New York, NY: McGraw-Hill; 2011. http://accessemergencymedicine.mhmedical.com/content.aspx?bookid=454&Sectionid=40199457. Accessed December 1, 2014.

High-dose insulin therapy in beta-blocker and calcium channel-blocker poisoning. Engebretsen KM et al. Clin Toxicol 2011;49:277-283.
Pubmed abstract

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Hypotension and Bradycardia in the Poisoned Patient
Post 1: Case and Differential Diagnosis
Post 2: Beta-Adrenergic Antagonists
Post 3: Calcium Channel Antagonists

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