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odbetablocker

beta adrenergic blocker overdose

general features of beta blockers in overdose:

  • more rapid onset of life-threatening features than with digoxin OD:
    • life-threatening CNS/CVS effects may occur within 30min of ingestion & death by 80min
  • much of the cardioselectivity is lost in OD thus features characteristic of all beta blockers in OD are:
    • bradycardia (~70%)
    • hypotension (~70%)
    • decreased level of consciousness (>55%)
    • respiratory failure (~40%)
    • hypoglycaemia (esp. children)
    • AV block
    • negative inotropy
    • bronchospasm (actually uncommon in OD)
    • mild hyperkalaemia (usually doesn't require Rx unless digoxin OD too)
  • mortality higher with propranolol than the cardioselective beta blockers because:
    • lipophilic ⇒ enters CNS ⇒ obtundation, resp. depression, seizures
  • seizures most probably result from combination of:
    • hypotension, hypoglycaemia, hypoxia & direct CNS toxicity
  • membrane stabilising (quinidine-like effect, also shown by nadolol & acebutalol):
    • impairs SA & AV nodal function ⇒ bradycardia & AV block
    • depressed ventricular conduction ⇒ wide QRS & occas. ventricular dysrhythmias
    • ⇒ VT, torsades, VF as well as bradyarrhythmias of other beta blockers
  • those with intrinsic sympathomimetic activity (pindolol carteolol) may cause sinus tachycardia
    • labetalol by blocking alpha receptors has an additional mechanism for causing hypotension

Mx of beta blocker overdose:

  • oxygen, monitor, IV line, ECG
  • consider activated charcoal if recent ingestion:
    • consider 4h administration if drug undergoes entero-hepatic circulation
  • if slow release formulation, consider whole bowel irrigation
  • use atropine prior to vagally-stimulating procedures (eg. intubation, gastric lavage)
  • propranolol overdose is managed primarily as a tricyclic antidepressant overdose (as early life-threats are due to its sodium-channel blocking effects) and secondarily as a beta-blocker overdose.

Mx of cardiac arrest

  • good CPR (cardioversion/defibrillation unlikely to help)
  • call an expert on toxicological arrests ASAP if possible
  • give boluses iv sodium bicarbonate 1-2mEq/kg every 1-2 minutes until return of perfusing rhythm
  • intubate and hyperventilate
  • give adrenaline as per usual cardiac arrest protocol
  • avoid amiodarone
  • consider 20% intralipid 100ml over 1 minute, repeat once or twice in 3-5 minute intervals if required, followed by an infusion
  • keep doing CPR

Mx of hypotension, bradycardia, AV block:

  • 1st line now should probably be High Insulin-Dextrose - Euglycaemia Therapy (HIET) as pig studies seem to show this is the only effective Rx.
  • IV atropine 0.02mg/kg children (min. 0.15mg) or 0.6mg adults:
    • tends to wear off quickly or be ineffective
  • IV glucagon:
    • half-life 20min
    • adults: 5-10mg bolus then infusion 2-5mg/hr
    • children: 0.05-0.1mg/kg bolus then 0.05-0.1mg/kg/hr infusion
    • NB. reconstitute in sterile water & dilute in 5% dextrose as its diluent (phenol) will eventually cause toxicity!!
  • 20ml/kg crystalloid solution to expand blood volume prn
  • if inadequate response, consider an inotrope with chronotropic activity at higher (perhaps 20x) than usual doses:
  • refractory cases of bradycardia require early pacing
  • refractory cases of hypotension:
    • peripheral arterial line and pulmonary artery catheter
    • may require IABP or cardiopulmonary bypass as the relatively short half lives (hours) means that these temporarising measures may be useful, as long as end-organ damage has not already occurred from prolonged hypotension
      • unproven benefit in beta-blocker overdose

Mx of ventricular arrhythmias:

  • usually treat VF/VT as per ACLS guidelines, avoiding VW class Ia & Ic drugs, ie. use lignocaine, DC;
  • treat torsade as usual:
    • over-drive pacing with isoprenaline or a pacemaker
    • magnesium sulphate

Mx of seizures:

  • check for & treat hypoglycaemia:
  • obtunded children should receive empiric 1-2ml/kg 25% glucose
  • 5% dextrose infusions generally have been sufficient to maintain euglycaemia, esp. if concomitant glucagon & catecholamines.
  • treat seizures as per usual

increasing elimination:

  • most have large Vd's & thus are not suitable for dialysis EXCEPTIONS are the hydrophilic ones with low protein binding & low Vd:

disposition:

  • if remain completely asymptomatic for 6hrs post-ingestion implies minimal risk unless slow-release formulation used
  • ⇒ can be discharged after psych. assessment with medical F/U in 24hrs
  • if slow-release preparation ⇒ admit
  • if hypotension, higher than 1st degree HB or haemodynamically significant arrhythmias ⇒ ICU
odbetablocker.txt · Last modified: 2012/01/25 10:53 (external edit)