Poisoning Flashcards
Diagnosis of poisoning/overdose is mainly from history however clinical sings/investigations may help you identify cause. State some potential causes of the following signs in poisoning/overdose:
* Tachycardia or irregular pulse
* Respiratory depression
* Hypothermia
* Hyperthermia
* Coma
* Seizures
* Constricted pupils
* Dilated pupils
* Hyperglycaemia
* Hypoglycaemia
* Renal impairment
* Metabolic acidosis
* Increased osmolality
Describe general approach to poisoning/overdose
- Bedside tests (ECG, ABG)
- Bloods (glucose, FBC, U&Es, LFTs, coagulation, always check paracetamol & salicyclate levels)
- Empty stomach if appropriate
- Consider specific antidote or PO activated charcoal
- Regular observations including BMs & urine output
- Consider ICU if respiratory depression
- Psychiatric assessment (MUST DETERMINE RISK e.g. intentions at time, present intentions, psychiatric history)
If unsure check toxbase
What amount of paracetamol, in mg/kg, can be fatal in adults?
150mg/kg
*However in malnourished pts 75mg/kg can be fatal
If pt is >110kg use weight of 110kg to avoid underestimating toxicity
What are symptoms & signs of paracetamol overdose/poisoning?
- Initially none, but may have vomiting or RUQ pain
- Later can develop jaundice & encephalopathy & AKI
State which pt groups are at increasd risk of developing hepatoxicity after paracetamol overdose
- Malnourished
- Taking liver enzyme inducing drugs (e.g. rifampicin, carbamezapine, phenytoin, chronic alcohol excess)
Remember acute alcohol intake at time of overdose actually thought to be protective
Discuss the management of paracetamol overdose (include management for different timings)
- If present within 1hr ingestion, activated charcoal may help
- If staggered overdose or timing unclear, start NAC straight away
- If <8hrs since ingestion and can act on blood results within 8hrs, take bloods and treat if above line. If can’t act on bloods within 8hrs, start NAC immediately
- If >8hrs and signifcant ingestion start NAC and stop if level below treatment line
Briefly outline the NAC regime
N-acetylcysteine given IV in 3 doses over ~21hr period.
- 150mg/kg in 5% glucose over 15-60 mins
- 50mg/kg in 500ml 5% glucose over 4hrs
- 100mg/kg in 1L 5% glucose over 16hrs
Discuss the ongoing management of paracetamol poisoning
- Do LFTs, coagulation (INR), U&Es next day and if INR raising continue NAC until INR <1.4
- Discuss with hepatology if continued deterioration
- Consider referral to specialist liver unit guided by Kings College Criteria
What is the Kings College Criteria for liver transplanation in acute paracetamol liver failure
Describe the pathophysiology of salicyclate overdose/poisoning in regards to acid base balance
- In mild toxicity, salicylates directly irritate the gastric lining. They can also cause ototoxicity through a multifactorial process, involving reduced cochlear blood flow secondary to vasoconstriction and changes to cochlear cells.
- In higher doses, the pharmacodynamics of salicylate poisoning leads to a mixed respiratory alkalosis and metabolic acidosis. In moderate/severe toxicity, salicylates stimulate the cerebral medulla, leading to hyperventilation and respiratory alkalosis.
- Metabolisation of salicylates then causes uncoupling of oxidative phosphorylation (reducing ATP production), resulting in anaerobic metabolism. This causes** heat production **and pyrexia and increased lactic acid production, resulting in metabolic acidosis. The acidic effects of salicylates also contribute to the associated acidosis.
- Hyperventilation then worsens in response to the acidosis until the body can no longer compensate.3,4
Salicyclate poisoning can be generally categorised into mild, moderate and severe. State some symptoms of each
Mild
* Nausea and vomiting
* Epigastric pain
* Tinnitus
* Dizziness
* Lethargy
Moderate
* Sweating
* Fever
* Dyspnoea
Severe
* Confusion
* Convulsions
* Coma
What might you find on clinical examination of pt with salicyclate overdose/poisoning?
Typical clinical findings in moderate/severe toxicity include:
- Warm peripheries and bounding pulse
- Tachypnoea and hyperventilation
- Cardiac arrhythmia
- Acute pulmonary oedema
What investigations would you do for salicyclate overdose/poisoning?
Bedside: ECG, ABG/venous gas, blood glucose (if not got venous gas), measure urine pH, consider catheterisation
Bloods: FBC, U&Es, LFTs, coagulation, salicyclate level, paracetamol level
NOTE: may need to repeat salicyclate levels after 2hr due to continued absorption. Also monitor serum pH & U&Es
Discuss the management of salicyclate overdose/poisoning
- If present within 1hr activated charcoal
- Urinary alkalinisation of urine with IV sodium bicarbonate (aim urine ph 7.5-8 & monitor K+ as hypokalaemia may occur)
- Consider haemodialysis (see separate FC for info)
No antidote for salicyclate poisoning- supportive care.
State some indications for haemodialysis in salicyclate overdose/poisoning
- serum concentration > 700mg/L
- metabolic acidosis resistant to treatment
- acute renal failure
- pulmonary oedema
- seizures
- coma
Remind yourself of signs of lithium toxicity
Explain how organophosphates cause poisoning/what do they do
State some symptoms of lead poisoning
- abdominal pain
- peripheral neuropathy (mainly motor)
- fatigue
- constipation
- blue lines on gum margin (only 20% of adult patients, very rare in children)
