The entry into the body of toxic substances in amounts which cause dysfunction of body systems

Causes

• Microorganisms (food poisoning)
• Fluids and gases (organic), eg. agricultural chemicals, petrol, paraffin, carbon monoxide
• Metal poisoning (inorganic), eg. lead, mercury, copper
• Alcohol and drugs (in excessive amounts)

For Food Poisoning, see p370

For Alcohol poisoning, see p367

Introduction

If possible, refer/admit all patients showing signs of poisoning to hospital. Send a note of what is known and what treatment has been given

Also refer/admit patients who have taken slow-acting poisons even if they appear well. These include:

• Aspirin
• Iron
• Paracetamol
• Tricyclic antidepressants, eg. amitriptyline, imipramine
• Paraquat
• Modified-release products

Even though it may not be possible to identify the poison and the amount taken, it is usually not important as:

• Only a few poisons have specific antidotes
• Few patients need active removal of the poison

Most patients must be treated symptomatically

However, knowledge of the poison will help you anticipate the likely effects on the patient

General measures

a) Respiration

Often impaired in unconscious patients

Ensure the airway is cleared and maintained - insert an airway if available
Position patient semi-prone to minimise risk of inhalation of vomit
Assist ventilation if necessary

b) BP

Hypotension is common in severe poisoning with CNS depressants. A systolic BP <70mmHg may cause irreversible brain or renal damage

Carry the patient head down on the stretcher and nurse in this position in the ambulance
Give oxygen to correct hypoxia
Set up an IV infusion (see p354)

Fluid depletion without hypotension is common after prolonged coma and after aspirin poisoning due to vomiting, sweating and hyperpnoea

Hypertension is less common but may be associated with sympathomimetic poisoning, eg. amphetamines, cocaine

c) Heart

Cardiac conduction defects and arrhythmias may occur in acute poisoning, especially with tricyclic antidepressants but these often respond to correction of any hypoxia or acidosis

d) Body temperature

Hypothermia: may develop in patients with prolonged unconciousness, especially after overdose of barbiturates or phenothiazines, eg. chlorpromazine, trifluoperazine

- it may be missed unless temperature is monitored
- treat by covering the patient with a blanket

e) Convulsions

Do not treat single brief convulsions

If convulsions are prolonged or recur frequently:

diazepam 10mg rectally repeated if necessary

HC2

child: 400 micrograms (0.4mg)/kg per dose
or diazepam 10mg slow IV repeated if necessary (max: 30mg) child: 200 micrograms (0.2mg)/kg

HC4

- do not give IM
- if IV route is not possible remove the needle of the syringe and give the dose rectally

Removal and elimination of the poison

a) Removal from the stomach

• Balance the dangers of attempting to empty the stomach with the likely toxicity of any swallowed poison as determined by the type of poison and amount swallowed

• Gastric lavage:

- only useful if done within 2 hours of poisoning (except with salicylates when it may be of use within 4 hours)

- seldom practicable or necessary before the patient reaches hospital

- do not attempt in drowsy or comatose patients because of the risk of inhaling stomach contents (unless there is a good cough reflex or the airway can be protected with a cuffed endotracheal tube)

- do not attempt with corrosive or petroleum products

• Use of emetics:

- of limited value, not very effective and may complicate diagnosis (especially with iron poisoning)

Only consider using:

- in fully conscious patients
- if poison is not corrosive or a petroleum product
- if poison is not absorbed by activated charcoal
- if gastric lavage is inadvisable or impossible

ipecacuanha syrup 0.14% 30mL followed by 200mL water child 6-18mths: 10mL older child: 15mL

- repeat once prn after 20 minutes
- vomiting usually occurs within 15-45 minutes of the first dose

b) Prevention of absorption of the poison

• Oral activated charcoal can bind many poisons in the stomach and so reduce their absorption

• It is more effective the sooner it is given but may still work up to 2 hours after poisoning (longer with modified-release products and anticholinergics)

• It is safe and especially useful for poisons toxic in small amounts, eg. antidepressants

• If patient unable to swallow the charcoal/water mixture (slurry), give by gastric lavage tube

Give activated charcoal 50g child: 25g (50g if severe)

- the dose-form of this drug currently available in Uganda is 250mg tablets. Grind these into a fine powder before mixing with 100-200mL of water (50g = 200 tablets of 250mg)

c) Active elimination of the poison

• Repeated doses of activated charcoal increase elimination of some drugs after they have been absorbed, eg. aspirin, carbamazepine, phenobarbitone, quinine, theophylline

Give activated charcoal 50g repeated every 4 hours

Treat any vomiting as this may reduce the effectiveness of the charcoal

In case of intolerance:

Reduce dose and increase frequency, eg. 25g every 2 hours or 10g every hour