discussion.

You might think this week's exercise feels a bit "high school", and to some extent it is. But, you need to think about what you are likely to be asked from a toxicologic perspective in the written exam, and the options are:
  1. The case of an unknown overdose, plus prop (ECG/ABG) to be interpreted, wit a question centering around differential diagnosis (e.g. long QT plus drugs that cause it, RAGMA on an ABG plus possible causes etc). Most of this you have covered to some degree in the ECG and ABG weeks, but it is worth making sure you are tight with it. 
  2. A known overdose, where you are asked to manage the patient.

It's this second one that specifically concerns us during the toxicology block. Most toxicology management questions can be distilled down to a good general answer (supportive care type stuff) with relatively few specifics thrown in to customise the answer. It's these specifics that you need to have foremost in your mind. We'll cover antidotes next week, but the other arms of management are:

Decontamination: which is aimed at reducing the level of exposure to a toxin that a patient receives
Enhanced elimination: which is used to increase the rate of removal of a toxin from a patient's body.
Common decontamination procedures include:
  • the use of single dose activated charcoal
  • gastic lavage
  • whole bowel irrigation

Common enhanced elimination techniques include:
  • multi-dose activated charcoal
  • urinary alkalinisation
  • haemodialysis or haemoperfusion
​DECONTAMINATION METHODS
Single dose charcoal is used to adsorb lipophilic molecules in the stomach/upper GIT and reduce the amount of a toxin available for absorption from the GI tract. It should be avoided in patients with compromised airways due to the risk of vomiting. It is not useful for hydrophilic molecules (acids, alkalis, metals or hydrocarbons). It is useful for (in order of exam likelihood):
  • Paracetamol
  • Tricyclic antidepressants (remember: watch the airway!)
  • Aspirin
  • Carbamazepine
  • Theophylline
  • Digoxin
  • Phenytoin
  • Barbiturates
Gastric lavage remains controversial, but is used for potentially lethal doses of toxins, or toxins that do not have an effective antidote. It requires an NGT and a protected airway/conscious patient. It should be avoided for corrosive agents (hydrocarbons, acids, alkalis etc). Think about it for:
  • Colchicine
  • Amanita Phalloides
  • Calcium channel blockers
  • Beta-blockers
​Whole bowel irrigation​ is used for similar indications to gastric lavage. You could add iron tablets to the list above.
ENHANCED ELIMINATION METHODS
​Multi dose activated charcoal is though to work by the phenomenon of intestinal dialysis. It may have a role in:
  • Carbamazepine
  • Theophylline
  • Quinine
  • Barbituates
  • Amanita Phalloides (although WBI is probably preferred)
Urinary alkalisation traps acidic toxins in the urine and increases their excretion. By far the most likely subject this will come up with is aspirin toxicity, and it will be mandatory to mention here. It may also be useful for phenobarbitone toxicity. (Note that the use of NaHCO3 in TCA toxicity is more to do with Na load and plasma/cellular pH than urinary pH.)
Haemodialysis works on the stuff that most of the other therapies on this list are useless for. That is, it's good for small, highly charged molecules that are usually excreted by the kidney:
  • Heavy metals and electrolytes
  • Toxic alcohols
  • Metformin
  • Methotrexate (or haemoperfusion)
  • Salicylates
  • Valproate
Note that none of these lists is particularly exhaustive. We've tried to hit the "likely" or "high yield" topics. It's crucial to have everything above straight in your mind before the exam, but if there's something you think we've missed, put it up to share on the VSG!