Beta blocker overdose

• Benzodiazepines - Flumazenil
• Ethylene glycol and methanol - Fomepizole and ethanol 10% IV
• Organophosphates - Atropine
• Warfarin - Factor II, VII, IX, X concentrate
• Cyanide - Dicobalt edetate and hydroxycobalamin
• Digoxin - Digibind
• β-Blockers - Glucagon
• Methaemoglobinaemia - Methylene blue
• Paracetamol - N-acetylcysteine
• Opioids - Naloxone

• Mixed overdose
• Interaction with other medications (especially antihypertensives)
• Elderly patients
• Cardiovascularly frail patients
• Sotalol and Propranolol are the most lethal beta blockers in overdose

Every patient suspected of having taken an overdose needs a paracetamol level checking.

These are Gs category G-protein coupled receptors.

β₁

• Heart
• Kidneys

β₂

• Lungs
• Muscle
• Blood vessels

• Causes blockade of sodium channels
• The QRS widens and there's a risk of ventricular arrhythmia
• It also crosses the blood brain barrier with direct toxic effects on the brain and spinal cord

• Causes blockade of potassium efflux
• This prolongs the QT and risks Torsades de pointes
• Often presents in asystole
• Can have delayed effects up to 24 hours after ingestion

Gladly.

• Sotalol comes as a racemate of the l-isomer and d-isomer
• The l-sotalol is the beta blocker, and not a very selective one at that
• The d-sotalol is a class III antiarrhythmic (potassium) and is responsible for the Torsades bit by blocking the delayed rectifier channel that permits timely repolarisation of the myocardium

Gets its own box because it's the most dangerous agent, largely because of its ability to cross the blood brain barrier, and its propensity to block sodium channels as well.

It's also one of the most commonly overdosed beta blockers.

• More than 1 or 2 grams is bad news
• Toxic effects will generally be seen within six hours

What it looks like

• Hypotension
• Bradycardia
• AV block
• PR prolongation
• Heart failure
• Cardiac arrest
• Bronchospasm
• Hypoglycaemia - reduced gluconeogenesis
• Hyperkalaemia - reduced insulin
• Drowsy or coma

Sometimes propranolol can look like a sodium channel blocker, because it is.

• Wide QRS
• Arrhythmias
• Seizures - directly enters the CNS and lowers seizure threshold

• As you would normally - if they can't protect their own airway, do it for them
• If you take enough of anything you can drop your GCS low enough to need a tube
• If you can safely avoid a tube, it allows you to monitor their neurological status more effectively
• Be cautious when intubating - these patients are cardiovascularly delicate

• If they have inadequate ventilatory effort - do it for them

err... that's it really

• IV access
• Fluid bolus (unless in frank pulmonary oedema)

For bradycardia:

• Atropine (most likely won't do much)
• Adrenaline 10-20 mcg bolus +/- infusion
• Isoprenaline up to 10 mcg/min infusion*
• Pacing - transcutaneous or temporary wire

For hypotension

• Fluid bolus
• Adrenaline as above if hypotensive and bradycardic
• Noradrenaline if primarily vasoplegic
• Insulin and dextrose (see below)
• Calcium as an inotrope

For Torsades

• Magnesium 10 mmol IV over 15 - 20 minutes
• Isoprenaline or pacing to maintain heart rate above 100

For QRS broadening and ventricular arrhythmias

• Sodium bicarbonate 2 mmol/kg IV
• Consider lidocaine
• Do not give amiodarone

Do an ECHO to determine whether the main issue is pump failure or vasodilatation and hypovolaemic shock.

*It's helpful to know what agent was ingested here - if they've had a load of selective B1 blocker, then giving isoprenaline (B2 agonist) for bradycardia is likely to worsen hypotension

We don't really know if it does anything useful, but the theory goes as follows:

• Glucagon triggers adenylate cyclase
• This increases cAMP production in cardiac myocytes
• This is essentially the same as activating all the blocked beta receptors
• Hey presto your heart rate, hypotension and lack of gluconeogenesis all magically improve

You give it as an infusion of up to 10 mg/hour IV.

This is becoming increasingly popular but we don't really know how it works.

• Insulin is a positive inotrope when you give lots of it, probably via its downstream effects on calcium
• It also helps supply sugar to the unhappy cardiac myocytes
• It sensitises everything to catecholamines
• It induces a bit of vasodilatation to help myocardial oxygen supply

The dose is anywhere from 0.5 to 10 unit/kg/hr.

How to do it:

• Bolus of 1 unit per kilogram IV
• If blood sugar <11 mmol/L then give 25g IV glucose at the same time
• Start IV infusion of 0.5 - 1 units/kg/hour
• Increase by 0.5 every 15 minutes until satisfactory response
• At the same time give 0.5 mg/kg/h glucose IV (10-20%) and titrate to keep blood sugar between 6 and 12 mmol/L

Monitor sodium, potassium, acid-base balance and glucose every 15 - 30 minutes until adequate response.