Poisoning

Published on 03/03/2015 by admin

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Last modified 03/03/2015

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13 Poisoning

Self-poisoning

This is a common problem, leading to over 100 000 hospital admissions in England and Wales per annum. It is also a problem in developing countries: in cities, drugs, e.g. diazepam, are used, while in rural areas substances such as copper sulphate and yellow oleander are often taken.

General points

• 80% of patients seen in A&E will be conscious.

• There is poor correlation between history of amount, type and timing of poisons consumed and blood toxicology.

• Frequently, more than one drug will have been consumed.

• Alcohol is the most commonly consumed second agent.

• Carefully assess suicide risk, be sympathetic and admit to MAU.

What particular points do you need to assess on physical examination?

• Assess and record conscious level using the Glasgow Coma Scale (p. 492).

• Document respiratory rate and cyanosis (use pulse oximetry).

• Measure blood pressure and pulse.

• Record pupillary size (small with opiates) and reactivity to light.

• Measure temperature: rectally if unconscious.

• If depressed consciousness, check for coexistent head injury.

• Look for needle tracks or signs of drug use.

Case history (1)

A 25-year-old woman is admitted semi-conscious, smelling of alcohol, having taken an indeterminate amount of an unknown drug at some point earlier that evening.

On examination she has depressed consciousness (GCS = 11), respiratory rate of 12 per minute, blood pressure of 95/70 mmHg and small reactive pupils.

What should you do?

• Baseline: full blood count, urea and electrolytes, liver function.

• Paracetamol and salicylate levels at 4 h or thereafter post-overdose.

• Blood and urine samples for toxicology: particularly useful in seriously ill with altered consciousness.

• O2 saturation, arterial blood gases if depressed respiration.

• Admit patient to MAU.

Information

Self-poisoning

Take advice from the 24-h National Poisons Information Service (see end of chapter) in all serious overdoses: there might have been recent advances in management of the specific poisoning under your care.

Some common drugs used for overdose exhibit delayed action, e.g. aspirin, paracetamol, tricyclic anti-depressants, iron (more common in children), co-phenotrope, paraquat and all modified-release preparations.

General management

• Nurse in left lateral position.

• Clear mouth of vomitus, debris, obstructing objects.

• Catheterisation of bladder is usually unnecessary as gentle suprapubic pressure can empty bladder.

• IV cannula.

• Nursing care of mouth and pressure areas.

Respiratory support

• Protect airway because vomiting is a risk: vomiting is particularly associated with opiates, benzodiazepines, alcohol and tricyclic anti-depressants.

• Respiratory depression might occur with opiates, benzodiazepines, alcohol, tricyclic anti-depressants.

• Monitor with pulse oximetry.

• Give oxygen: start with 60% humidified O2.

• Loss of gag or cough reflex is the prime indication for intubation.

Cardiovascular support

• Watch for hypotension (systolic BP below 80 mmHg):

• Mild: raise end of bed
• Severe: use IV volume expanders, e.g. dextran
• Very severe: insert CVP line to monitor fluid replacement
• Measure urine output: aim for 0.5 mL/kg/h. Urine output is a useful guide to the adequacy of the circulation.

• Monitor ECG for arrhythmias.

What other problems might occur?

Blood pressure

• Watch for hypotension (see above).

• Avoid vasopressant drugs because these might interact adversely with the poison.

• Less commonly, transient hypertension might be seen with amfetamine and cocaine.

Arrhythmias

• Might arise from hypoxia or metabolic acidosis.

• Bradycardia might occur with beta blockers, digoxin and organophosphorus compounds.

• Ventricular and supraventricular tachycardias occur due to theophyllines, tricyclic anti-depressants/phenothiazines (due to prolonged QT interval) cocaine, Ecstasy and amfetamine.

Hypothermia

• Can occur due to unconsciousness, especially with phenothiazines and barbiturates.

• Measure temperature rectally.

• Nurse under space blanket with warming, if needed, using water bottles.

Hyperthermia

• Can occur with amfetamines, Ecstasy and cocaine, selective serotonin reuptake inhibitors (SSRIs), salicylates and tricyclic anti-depressants.

What specific management procedures are there for overdoses?

Reducing absorption

• Gastric lavage: should only be used for life-threatening overdoses and only within the first hour for significant recovery of poison. Avoid lavage if corrosives, paraffin or petrol have been taken because of risk of inhalation. Always intubate if the patient is unconscious.

• Induced emesis: should not be used because it is ineffective at removal of poison and delays the use of activated charcoal.

• Activated charcoal: binds drugs in the intestine and is valuable for adsorbing most poisons but is most effective for aspirin, tricyclic anti-depressants and theophyllines. For most drugs do not use more than 1 h post-ingestion of poison or with an oral antidote (see also Active elimination, below).

Active elimination

• Repeated doses of charcoal might enhance elimination for selected drugs even after the drug has been absorbed. This works for aspirin, barbiturates, quinine, theophylline and carbamazepine.

• Whole bowel irrigation using non-absorbable polyethylene glycol solution (not to be confused with ethylene glycol or anti-freeze) causes loose stool and forces bowel contents through, rapidly reducing absorption. This is not routinely used.

• Forced diuresis for salicyclate poisoning is dangerous and should not be used.

• Urine alkalinisation is mainly used for salicylate overdose (see p. 403).

• Haemodialysis helps in severe salicylate poisoning, barbiturates, ethylene glycol, alcohol and lithium poisoning.

• Haemoperfusion involves passing heparinised blood across absorbents such as charcoal. Works for barbiturates and theophylline.

Antagonising the influences of poisons

• Acetylcysteine or methionine replenishes cellular glutathione stores in paracetamol poisoning.

• Ethanol is a competitive inhibitor of alcohol dehydrogenase and is given in ethylene glycol (anti-freeze) poisoning. Fomepizole is also useful when ethanol is contraindicated, e.g. previous excess alcohol user or liver disease.

• Naloxone and opiates compete at the same receptor.

Progress.

The partner of this 25-year-old patient came to the MAU shortly after admission. He had found two empty boxes of diazepam which she had been taking for acute anxiety over the last few months. He said that her drug misuse might be related to her being made redundant a week ago. She did not require ventilation and woke up gradually. She was very tearful and apologetic and did not require psychiatric referral after counselling.

Benzodiazepine overdose

Benzodiazepines account for 40% of all overdoses.

Clinical features

• Drowsiness, ataxia, slurred speech, coma

• Respiratory depression and hypotension might occur.

Management – the problems

Respiratory depression or in combination with alcohol – vomiting and aspiration.

Treatment – supportive

• Protect airway and neurological observations.

• Gastric lavage is not required.

• Flumazenil is a benzodiazepine antagonist that can be used in severe overdose with marked respiratory depression only.

• Beware: seizures have followed flumazenil administration.

• Patients are usually fit to be discharged at 24 h.

Paracetamol (acetaminophen) poisoning

Remember

• Paracetamol is consumed in 45% of overdoses in the UK

• As little as 7.5–15 g (15–30) tablets can cause severe hepatic necrosis.

Case history (2)

A young woman, aged 18, was brought into A&E by her boyfriend, who had found her drowsy. A tablet packet – possibly containing paracetamol tablets – and half a bottle of wine was found near her. They had argued the previous night and she had threatened suicide. He thought that she had taken the tablets 6 h ago. A past history of an eating disorder was elicited.

On examination she was very thin and had a GCS of 10. There were no other physical signs.

Investigations

• Baseline urea and electrolytes

• Liver function (including INR) and biochemistry

• Paracetamol and salicylate levels

This patient’s paracetamol level was 140 mg/L and her salicylate level was < 10 mg at 6 h post-overdose. She was admitted to MAU.

Points to remember

• Nausea and vomiting are extremely common in first 24 h.

• Abdominal pain 24 h plus.

• Persistent nausea with subcostal pain usually indicates significant hepatic necrosis.

• Chronic alcohol excess or other enzyme-inducing drugs increase metabolism of drugs.

• Hypoglycaemia may occur.

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