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

Table 80.2 Clinical effects of the common poisons

INVESTIGATIONS

Important initial investigations include:

• : 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.

EMESIS

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

WHOLE BOWEL IRRIGATION

This is a newer method of gastric decontamination that is indicated for a limited number of poisons.⁸ Whole bowel irrigation involves administration of non-absorbable polyethylene glycol solution to cause a liquid stool and reduce drug absorption by physically forcing contents rapidly through the gastrointestinal tract. Polyethylene glycol preparations are still occasionally used in surgical units for ‘bowel preparation’ prior to surgery. It may have arole in treating large ingestions of drugs that are not absorbed by AC. Indications include large ingestions of iron or lithium, ingestion of drug-filled packets/condoms (‘body packers’), and large ingestions of sustained-release or enteric-coated drugs (e.g. theophylline or calcium channel blockers). At present, efficacy is based on case reports alone.

URINARY ALKALINISATION

Urinary alkalinisation (previously termed forced alkaline diuresis) may be useful for serious poisonings with:

Intravenous sodium bicarbonate (approximately 1.26%) is infused to maintain a neutral balance and attempt to achieve a urine pH of approximately ≥ 7.5. The term ‘urine alkalinisation’ emphasises that urine pH manipulation is the prime objective of treatment; the terms ‘forced alkaline diuresis’ and ‘alkaline diuresis’ should be discontinued. According to international position statements it should be considered the treatment of choice for moderate to severe salicylate poisoning.⁹ Care must be taken to ensure the potassium does not fall rapidly.

EXTRACORPOREAL TECHNIQUES

Numerous extracorporeal techniques are potentially available to aid drug removal in the poisoned patient. These include plasmapheresis, haemodialysis, haemofiltration, haemodiafiltration and haemoperfusion. There are limited data on drug clearance by these techniques in the literature and it is not possible to extrapolate from one system to the other. At present, knowledge of the principles of the methods and the kinetics of the drug involved is relied upon.

Extracorporeal techniques should only be considered when there are clinical features or markers of severe toxicity, failure to respond to full supportive care coupled with poisoning by a drug that can potentially be removed. Impairment of the normal route of elimination of the compound may also influence the decision. Use of extracorporeal techniques is probably only worthwhile if total body clearance is increased by at least 30%. Haemoperfusion is rarely performed in most intensive care units and intermittent haemodialysis is often confined to renal units. Consequently, the use of continuous haemofiltration, with or without dialysis, using filtration rates of greater than 50–100 ml/kg per hour, is likely to be as equally effective as when an extracorporeal technique is indicated.

AMPHETAMINES (INCLUDING ‘ECSTASY’, MDMA)

BARBITURATES

BENZODIAZEPINES