General Approach (Sources: Revision notes)

Question 1

What is the general approach to a patient with poisoning?

Answer 1

ABCD
Identify agent and quantity taken
Drug manipulation to limit absorption and maximise excretion
Specific antidotes
General supportive care

Question 2

Where should you get further advice on poisoning? (UK)

Answer 2

The National Poisons Information Service has an online service www.toxbase.org and a 24/7 telephone service

Question 3

What are the important factors in a history of a patient with poisoning?

Answer 3

Info regarding the toxin - if tablets - number, strength, time period there were taken over
For other toxins - mode of exposure, exact nature of toxin - packaging always useful, duration of exposure
Any first aid measures
Other medications
Alcohol use
Chronic liver or renal dysfunction
Current symptoms

Question 4

What investigations would you do in a patient with poisoning?

Answer 4

Identification of toxin- urinalysis
Identification of factors that may impact toxin clearance - e.g. renal function, liver function
Assessment of physiological derangements associated with the toxin- - biochem, ABG, anion gap, ECG
Plasma drug levels e.g. paracetamol, salicylate, ion, digoxin, lithium, some anti-epileptics

Question 5

How can you limit absorption of a toxin?

Answer 5

Gut decontamination

• induced emesis - historical and no longer used
• gastric lavage - irrigation of the stomach by injecting and aspirating water NG, only beneficial within 1 hour of OD, should not be attempted if corrosives ingested
• Activated charcoal - porous substance with large SA, bind she majority of ingested toxins (except heavy metals, strong acids, alkali, cyanide and alcohols).
• Whole bowel irrigation

Question 6

Which toxins is activated charcoal not effective for?

Answer 6

heavy metals
strong acids and alkalis
cyanide
Alcohols

Question 7

When should activated charcoal be given?

Answer 7

Within 1 hour of ingestion
Therapeutic window is however extended in drug that slow gastric emptying (opiates, TCAs) or those that exhibit entero-hepatic recirculation e.g. carbamazepine, theophylline, digoxin, quinine and phenobarbital - AC may be effective for up to 4 hours
Repeat doses may be helpful in ODs with sustained release drugs

Question 8

Discuss whole bowel irrigation for limiting absorption of toxins

Answer 8

Non-absorbable polyethylene glycol is infused down an NG causing rapid expulsion of gut contents as liquid stool
May be employed for those agents not absorbed by AC or in those with non-absorbable but potentially dangerous objects in their gut - e.g. ‘body packers’

Question 9

How is elimination of toxins enhanced?

Answer 9

Forced alkaline diuresis
Renal replacement therapy
Haemoperfusion

Question 10

Describe forced alkaline diuresis

Answer 10

The elimination of acidic drugs with low pKa may be enhanced by forced alkaline diuresis
Required infusion of IV sodium bicarb with a view to increasing urinary pH to around 7.5
The acidic drug molecules, which are normally filtered at the glomerulus and then reabsorbed, convert to the ionic form within the abnormally alkaline conditions of the tubule and are therefore not reabsorbed
Classically used in aspirin poisoning but may also have a role in methotrexate and phenobarbital

Question 11

Describe the use of renal replacement therapy to improve drug elimination in OD

Answer 11

Most effective for drugs that are
 - small (MW < 500Da)
- low protein binding
-small volume of distribution
Very high replacement rate may be required (50-100ml/kg)

Question 12

What is haemoperfusion?

Answer 12

A charcoal cartridge replaces the dialysis membrane with in the extracorporeal circuit
More effective at removing larger molecules
Expensive with limited availability with no evidence of superiority to more conventional techniques
Theoretical advantage in poisoning with theophylline, carbamazepine, verapamil, phenobarbital and paraquat.

Question 13

What is a toxidrome?

Answer 13

Many of the agents associated with OD manifest with similar symptoms, these are classified into toxidrome
These are:
Cholinergic's
Anticholinergics
opioid
Hypo-sedative
Serotonin syndrome
Sympathomimetic

Question 14

Describe the features of a cholinergic overdose

Answer 14

Confusion, decreased conscious state, salivation, bronchorrhoea, bronchospasm, bradycardia, emesis, incontinence, abdo cramps, sweating, hypotension

Question 15

What toxins cause cholinergic symptoms?

Answer 15

Organophosphates

Some fungi

Question 16

What are the management principles of a cholinergic overdose?

Answer 16

Anticholinergics -atropine
Anti cholinesterase reactivate - pralidoxine
Benzos

Question 17

What are the features of an anti-cholinergic overdose?

Answer 17

tachycardia, hypotension, confusion, coma, dry skin, fever, flushing, ileum, urinary retention

Question 18

What drugs cause anti-cholinergic symptoms?

Answer 18

Antihistamines
Anti-depressants
Anti-parkinson drugs
anti-psychotics
atropine

Question 19

What are the key features of an opioid overdose?

Answer 19

Coma, pinpoint pupils, respiratory depression, bradycardia, hypotension

Question 20

What are the key features of the hypo-sedative toxidrome?

Answer 20

ataxia, CNS depression, coma, nystagmus, hypotension, hypothermia

Question 21

What drugs cause the hypo-sedative toxidrome?

Answer 21

Benzodiazepines, barbituates, anti-depressants, alcohols, Gamma-hydroxy-butyric acid

Question 22

Describe the features of serotonin syndrome

Answer 22

Altered mental status
Autonomic dysfunction
neuromuscular hyper-activity

Question 23

What drugs cause serotonin syndrome?

Answer 23

Anti-depressants
Amphetamines
Ecstasy

Question 24

What are the key features to treating serotonin syndrome?

Answer 24

benzos

serotonin antagonist - cyproheptadine

Question 25

What are the key features of sympathomimetic overdose?

Answer 25

delusions
paranoia
tachycardia
hypertension
hyperreflexia
diaphoresis
piloerection

Question 26

What drugs cause the sympathomimetic toxidrome?

Answer 26

amphetamines
cocaine
sympathetic agents e.g. pseudo ephedrine, salbutamol