Poisoning and Overdose
·
Cause of significant proportion
of arrests in 18 – 35 year olds
·
Duration of arrest and dose of
toxin determinants of survival
·
Do general management
·
Manifestations of poisoning:
o Exaggerated therapeutic response (eg sedation with BZD)
o Pharmacological effects (eg respiratory depression, convulsions)
o Accidental: children, single poison
o Intentional: adult, often multiple, taken in conjunction with alcohol
·
Management:
o History:
§ Find out the drug if you can (has someone brought in the packet?): but
only a few will change management (paracetamol, salicylates, lithium, paraquat,
quinine, phenobarbitone, iron salts)
§ Very unreliable – especially the number of tablets taken
o Supportive treatment:
§ A,B,C: Respiratory depression is the most common cause of death.
§ Maintain airway, check blood gases. Check for hypotension (®raise legs except in heart failure, volume expanders). Monitor electrolytes
§ Maintain safety: close supervision, no access to drugs on ward, etc
o Intensive support treatment: IV fluids, ?NG tube, maintain vital functions, nursing care (eg suction, pressure sores, limb movement ® ¯thrombosis)
o Treat complications: hypothermia, hyperthermia (salicylates and stimulants – sponge down, use fan), seizures (iv diazepam), arrhythmias (leave bradycardia, tachycardia – correct acidosis, try amiodarone), hypoglycaemia (salicylates, oral hypoglycaemics)
o Plus treatment specific to poison
o Mental health assessment
· Investigations:
o Blood levels: sometimes useful (eg Li, aspirin, theophylline, carbamazepine). Waste of time for TCAs
o Urine Screen: Rarely changes management, no quantitative information,
really only for criminal cases (eg after MVA)
·
Corrosives:
o Never induce vomiting
o Drink copious fluids
o Soak eyes, skin, mucous membranes
o Petroleum: beware of inhalation, cup of milk
·
Eliminating poisons. If sure it‟s
not petroleum products, caustics, corrosives or acids, then options may
include:
o Activated charcoal
§ Better than emesis
§ Charcoal powder, mixed with H2O: needs to be within 60 minutes. Give SINGLE 50 g dose in an adult (1 g/kg)
§ Reduces GI absorption of paracetamol, aspirin, phenytoin, digoxin, TCAs,
theophylline, carbamazepine.
§ Don‟t use for volatile hydrocarbons or corrosives or an unprotected
airway
§ Good for unionised drugs. Does not bind with acids, alkalis, alcohols,
lithium.
§ Generally safe but constipation, aspiration may be problems (protect
airway)
o Multiple doses only for drugs undergoing enterohepatic circulation or
diffusing into the gut Þ drugs with a small Vd, low clearance, low protein binding and long T½.
Eg Theophylline, carbamazepine, quinine, phenobarbitone. NOT Paracetamol.
·
PH adjusted diuresis:
o Alkaline diuresis: aspirin, phenobarbitone
o Acid diuresis: amphetamine, methadone.
Doubtful use and dangerous
·
Dialysis: Haemodialysis. Only
useful if low Vd, small molecule and low protein binding (eg lithium,
theophylline, salicylates, alcohol and barbiturates)
·
Whole bowel irrigation: „Go
Lightly‟ – Xray prep
·
Questionable effectiveness:
o Emesis: Not effective? Ipecac – never if airway reflexes not intact.
Causes emesis in 90% within 15 – 30 minutes
o Gastric lavage: large bore catheter through mouth. 1ml/kg of body
temperature water, recover, repeat. Little evidence of benefit and risk of
aspiration. Contraindicated if acid, alkali, or petroleum
·
Paracetamol
o Walk in, conscious
o RUQ pain
o Conjugation pathway easily saturated. Of the remainder, 15% is
metabolised to a metabolite that combines with glutathione. If glutathione is
depleted, metabolite causes hepatic damage
o Toxic dose 140 mg/kg (textbook), 200 mg/kg (Starship), lower if chronic
alcoholism, enzyme inducing drugs or fasting
o Measure plasma concentration. Treat if > 200 mg/ml, 100
if liver disease, anorexia, etc. Threshold declines for each hour after
ingestion
o Absorbed quickly so gastric lavage or activated charcoal only effective
within 45 minutes
o N-acetylcysteine (NAC) best antidote – saturates alternative pathway so
all the paracetamol is metabolised through the main pathway. Normal dose is 10
- 15 mg/kg per 4 hours acutely, per 6 hours at home
o Monitor AST/ALT, PT (INR)
· TCAs: see Topic: Tricyclic Antidepressants
· MAOIs: see Topic: MAOIs (Monoamine Oxidase Inhibitors)
· Opioids:
o Marked sedation, pinpoint pupils, ¯¯ respiration (differential:
stroke)
o Naloxone (but short T½ ® will lapse back)
· Stimulants (cocaine type drugs): BP, tachycardia, arrhythmia, dilated pupils [sympathetic effects], seizures
· Barbiturates ® flumazenil (can cause seizures – so not if SSRIs/TCAs/antihistamines as well – which also cause seizures)
· Dibenzazepine antidepressants: Rapidly absorbed, high Vd, protein bound. Look for myocardial toxicity, hypotension, hyperreflexia, convulsions. Treatment supportive + naso-gastric tube and charcoal (up to 24 hours later). Monitor ECG, iv propranolol and NaHCO3
· Benzodiazepines: Diazepam, temazepam ® Post –OD “cerebellar syndrome” (dizziness, confusion, ataxia, nystagmus, bullous lesions). Supportive treatment
·
Anticonvulscents: carbamazepine
· Bronchodilators: theophylline
· Cocaine ® benzodiazepines
· Carbon Monoxide ® 100% oxygen, treat cerebral oedema. Presentation: pink, headache, vomiting, tachycardia, seizures, arrest
·
Cyanide ® 100% O2
+ cobalt edetate
·
Methanol and ethylene glycol
poisoning ® correct acidosis, ethanol
·
Chelating agents for arsenic,
copper, lead, iron, cyanide
·
Aspirin: risk is pH balance
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