Management of acute poisoning

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Chapter 80 Management of acute poisoning

Acute poisoning remains one of the commonest medical emergencies, accounting for 5–10% of hospital medical admissions. Although in the majority of cases the drug ingestion is intentional, the in-hospital mortality remains low (< 0.5%).¹ There are specific antidotes available for a small number of poisons and drugs; however, in most intoxications, basic supportive care is the main requirement and recovery will follow. This chapter is a hands-on guide to the general management of acute poisoning and drug intoxication. Larger reference books should be sourced, or internet-based information services (e.g. Toxbase – http://www.spib.axl.co.uk) referred to, if specific detail is required.

Clinical toxicology remains an experience-based specialty; consequently, many recommendations are based on a small literature of case reports, rather than controlled clinical studies. In recent years, toxicological experts have produced position statements and clinical guidelines on certain aspects of care, and these will be referenced when possible.

GENERAL PRINCIPLES

The general principles of the management of poisoned patients are diagnosis, clinical examination and resuscitation, investigations, drug manipulation, specific measures and continued supportive care. In the more acute situations, these actions often have to be carried out simultaneously.

AIRWAY AND VENTILATION

In acute poisoned patients who are unconscious, dentures should be removed and the oropharynx cleared of food and vomit. Tracheal intubation and airway protection is almost always necessary when a patient tolerates insertion of an oropharyngeal airway. Inadequate spontaneous ventilation, determined clinically or by arterial blood gas (ABG) analysis, obviously requires ventilatory support. Venous access should be established, and circulatory assessment must be made. Basic observations, including blood pressure, pulse rate, peripheral perfusion and urine output, should be recorded. There are very few tricks or traps as to the use of invasive monitoring and inotropic drugs, and the principles are similar to those covered elsewhere in this book.

CLINICAL EXAMINATION

A standard clinical examination should be carried out, looking particularly for needle marks or evidence of previous self-harm. The Glasgow Coma Scale, although designed for head-injured patients, is frequently used. However, descriptive documentation of the degree of impaired consciousness is much more valuable. When patients are unconscious and no history is available, the diagnosis depends upon excluding other common causes of coma (Table 80.1) and consideration of any circumstantial evidence. Specific attention should be paid to the temperature, pupil size, respiratory and heart rate, as these may help to restrict the list of potential toxins (Table 80.2).

Table 80.1 Common causes of coma other than acute poisoning

Intracranial bleeds

Subarachnoid haemorrhage

Subdural/extradural haematomas

Meningitis or encephalitis

Diabetic comas

Uraemic encephalopathy

Table 80.2 Clinical effects of the common poisons

Convulsions	Tricyclics, isoniazid, lithium, amfetamines, theophylline, carbon monoxide, phenothiazines, cocaine
Skin
Bullae	Barbiturates, tricyclics
Sweating	Salicylates, organophosphates, amfetamines, cocaine
Pupils
Constricted	Opioids, organophosphates
Dilated	Hypoxia, hypothermia, tricyclics, phenothiazines, anticholinergics
Temperature
Pyrexia	Anticholinergics, tricyclics, salicylates, amfetamines, cocaine
Hypothermia	Barbiturates, alcohol, opioids
Cardiac rhythm
Bradycardia	Digoxin, β-blockers, organophosphates
Tachycardia	Salicylates, theophylline, anticholinergics
Arrhythmias	Digoxin, phenothiazines, tricyclics, anticholinergics

INVESTIGATIONS

Important initial investigations include:

• Urinalysis: with a sample kept for later analysis if required (rapid reaction dipsticks are available to screen for common drugs of abuse/recreational drugs; however, their reliability is questioned by some).

• Basic biochemistry: many drugs are dependent on renal elimination. Significant renal insufficiency may alter management.

• ABG analysis: Metabolic and/or respiratory acidosis is most common. Aspirin may initially cause a respiratory alkalosis. Metabolic alkaloses are unusual.

•

: It is normally 10–14. Ethanol, methanol, ethylene glycol, metformin, cyanide, isoniazid or salicylates are the most frequent causes a high anion gap metabolic acidosis in clinical toxicology.

• Osmolal gap: this is the difference between the laboratory measured osmolality (O_m) and the calculated osmolality (O_c). O_c = 2(Na⁺ + K⁺) + urea + glucose. The osmolal gap is normally < 10. Causes of a raised osmolal gap are ethanol, methanol and ethylene glycol.

• Chest X-ray: inhalation of gastric contents is not uncommon.

• Drug levels: these are rarely helpful except in specific poisonings. They include paracetamol, salicylates, iron, digoxin and lithium.

GUT DECONTAMINATION

Ipecacuanha-induced emesis is no longer recommended for two reasons:² first, it is ineffective at removing significant quantities of poisons from the stomach and, second, it limits the use of activated charcoal.

GASTRIC LAVAGE

Unless performed within 1 hour of drug ingestion, it is no longer recommended.³ The joint American and European toxicologists’ statement states that if performed after this time the amount of poison removed is insignificant, and lavage may only propel unabsorbed poison into the small intestine. However, this view has recently been questioned and is based on limited data.⁴ Prior intubation is essential when laryngeal competence is absent or doubtful, especially because, in the majority of overdoses, pulmonary aspiration is more lethal than the ingested drug.

To perform gastric lavage, the patient should be positioned head-down on the left side, and then a large-bore tube (36–40 Fr) with large side holes is passed into the stomach. The tube is aspirated before lavage is started, then tepid water instilled and recovered completely before continuing. The lavage is repeated until the return is clear; stomach massage or gastroscopy may assist removal of coalesced drug masses. Sodium, water and heat balance are of major importance in children. Gastric lavage is contraindicated in ingestions of corrosives, caustics and acids as oesophageal or gastric perforation may occur. Inhalation of petrol, paraffin or white spirits can cause intense pneumonitis.

ACTIVATED CHARCOAL

Activated charcoal (AC) remains the first-line treatment for most acute poisonings.⁵ Owing to its large surface area and porous structure it is highly effective at adsorbing many toxins with few exceptions. Exceptions include elemental metals, pesticides, strong acids and alkalis, and cyanide. It should be given to all patients who present within 1 hour of ingestion, although it is also acceptable to administer it after 1 hour if it follows an overdose of a substance that slows gastric emptying (e.g. opioids, tricyclic antidepressants). Because of international guidelines recommending administration of AC within 1 hour, it is vital to identify rapidly those who present after a potentially serious overdose so that it can be given swiftly.⁶

Repeated doses of AC can increase the elimination of some drugs by interrupting their entero-enteric and enterohepatic circulation. Indications for repeated dose AC are shown in Table 80.3.⁷ AC is given in 50 g doses for adults and 1 g/kg for children. It commonly causes vomiting; therefore consider giving an antiemetic prior to administration. Repeated doses are given at 4-hourly intervals.

Table 80.3 Drug intoxications where multiple-dose activated charcoal may be beneficial

Sustained-release preparations