FRCA Notes

General Approach to the Poisoned Patient

Resources

  • In general, the poisoned patient should be assessed initially using an A-E approach
  • Several classes of drugs produce stereotyped toxidromes, however there are overlapping features and ingestion of multiple medications/drugs may alter the typical picture expected
  • As such, below is a generic approach to any patient with a (suspected) history of drug toxicity or poisoning

ECG

  • An initial ECG should be routinely performed in all poisoned patients, as it may provide both diagnostic and prognostic information
  • Serial ECGs may be required for several hours to monitor for progression or delayed effects
  • Features may include:
    • Bradycardia ± AV block e.g. β-blockers, calcium channel blockers, digoxin, opioids and organophosphates
    • Tachycardia e.g. sympathomimetics (cocaine, amphetamines) or anticholinergics (TCA's)
    • Prolonged QRS interval e.g. fast sodium channel blockade
    • Prolonged QT interval e.g. TCA's, antihistamines and anti-arrhythmics
    • Myocardial ischaemia e.g. cocaine

Laboratory

  • FBC
  • Venous blood gas
  • Urea and creatinine
  • Electrolytes
  • CK
  • Liver function tests
  • Clotting studies
  • Pregnancy test
  • Blood drug levels e.g. paracetamol level, salicylate level

  • There are immunoassay and/or urine toxicology screens for various agents and their metabolites
    • Opioids, benzodiazepines, cocaine and tricyclics
    • Results do not provide information on nature, timing or degree of exposure

  • Arterial blood gas and anion gap
    • The normal anion gap is 8 - 16mmol/L
    • A raised anion gap implies the presence of unmeasured anions, be they exogenous (salicylates, toxic alcohols) or endogenous (lactate, urea)

  • Serum osmolar gap
    • This is the difference between the measured and calculated osmolality
    • Calculated osmolality = 2[Na+] + [urea] + [glucose]
    • The normal osmolar gap is <10mOsm/kg
    • A high gap implies the presence of an osmotically active molecules such as ethanol, methanol or ethylene glycol

  • No RCT has demonstrated a morbidity or mortality benefit

  • Activated charcoal 1g/kg is the preferred method
    • Administered within 1hr of ingestion PO/NG
    • Adsorbs toxin molecules to reduce risk of absorption
    • May cause aspiration and is contraindicated if unprotected airway

  • Other methods:
    • Gastric lavage: less effective than charcoal and is associated with a higher risk of aspiration
    • Induced emesis: e.g. with ipecacuana does not improve outcome
    • Whole bowel irrigation: e.g. enteral administration of polyethylene glycol may be beneficial for agents not well-adsorbed by activated charcoal e.g. lithium

Hypotension

  • Typically managed with IV fluid
  • Refractory hypotension may require invasive monitoring + vasopressors
  • Use positive inotropes with caution as may precipitate arrhythmias

  • May need to use specific antidotes in particular aetiologies:

Arrhythmia

  • Correct aggravating factors, including hypoxia, hypercarbia, acidosis and electrolyte abnormalities

  • Bradyarrhythmias can be managed as per Resus UK guidelines ± use of specific antidotes
  • QRS widening and tachyarrhythmia in the context of TCA overdose requires treatment with sodium bicarbonate
  • Torsades de pointes can be seen in overdose of QT-prolonging drugs and should be treated with magnesium e.g. 2g over 2-5mins
  • Narrow-complex tachycardias may be due to hyperadrenergic states (e.g. cocaine or amphetamines); benzodiazepines may be effective but DCCV or β-blockers less so

Seizures

  • Ensure correction of electrolyte abnormalities and glucose
  • Benzodiazepine therapy as standard
  • Tend to avoid phenytoin as it may exacerbate the clinical picture
  • Can give pyridoxine (vitamin B6) for isoniazid overdose
  • Ensure they hypoglycaemic alcoholic receives some thiamine before any glucose

Hyperthermia

  • Active cooling is generally advised once >39°C as, above this temperature, complications such as AKI, rhabdomyolysis and DIC may occur
  • General measures including removing clothing/covering, ice packs in groin/axillae and cool IV fluids
  • Benzodiazepines may help those in hyper-adrenergic states
  • Refractory hyperthermia should prompt discussion with a clinical toxicologist, and use of dantrolene or cyproheptadine may be recommended

  • Alkalinisation of urine, for example with sodium bicarbonate, may enhance the excretion of weak acids
  • Alkalinisation favours dissociation into H+ and the weak acid (A-)
  • The dissociated weak acid is more readily excreted
  • Examples include salicylate and phenobarbital poisoning

  • Haemofiltration, dialysis or even plasmapheresis may be considered in severe poisoning
  • It works well for low-molecular weight, minimally protein bound and low-volume of distribution poisons
  • Examples include salicylates, lithium and toxic alcohols


Poison Antidote or treatment
Paracetamol NAC
β-blocker High-dose insulin euglycaemic therapy (/Glucagon)
Calcium channel blocker High-dose insulin euglycaemic therapy (/calcium)
Digoxin Digoxin-specific antibodies
Opioids Naloxone
Benzodiazepines Flumazenil
Local anaesthetics Intralipid
Iron Desferrioxamine
TCA Sodium bicarbonate
Heavy metals EDTA
Cyanide Dicobalt edetate or hydroxycobalamin
Organophosphates Pralidoxime (+ Atropine)
Methanol or ethylene glycol Ethanol ± fomepizole (alcohol dehydrogenase antagonist)