Gastrointestinal decontamination in poisoning

What it is

Decontamination is the neutralization or removal of a poison. External decontamination covers the eye and the skin; internal decontamination of the gut is gastrointestinal decontamination, which means functionally removing an ingested toxin from the gastrointestinal tract in order to decrease its absorption.

The approaches fall into three groups:

• Gastric evacuation, by forced emesis or gastric lavage.
• Intra-gastric binding, most commonly by single or multidose activated charcoal.
• Speeding transit of toxins to decrease total absorption time, by whole bowel irrigation or cathartics.

Endoscopy, surgery and dilution are also listed among the options.

Decontamination of the gut is most likely to help patients who present for care soon after ingestion, usually within one to two hours, who have ingested a poison and an amount suspected to cause toxicity, and who do not have clinical factors such as somnolence that make decontamination dangerous.

How it is treated

Gastric lavage, or stomach pumping, is considered for a recent ingestion, under one hour, of a life-threatening amount of a toxin for which there is no effective treatment once absorbed. The airway is secured first, the patient is placed in the left lateral decubitus position with the head end lowered, and a thick orogastric tube of 28 to 40 is inserted into the stomach. Gastric content is aspirated, then warm water or NS is infused slowly in aliquots of 3 to 4 ml/kg, aspirated, and the cycle repeated until the return is clear. A dose of activated charcoal at 1 g/kg is added, and the first 100 ml recovered is sent for a toxin screen. Lavage must not be used with an unprotected airway, which is why endotracheal intubation comes first in a comatose patient, nor after a caustic or corrosive ingestion because of perforation, nor after a hydrocarbon of low viscosity because of aspiration, nor in a patient at risk of gastrointestinal hemorrhage or perforation. An uncontrolled convulsion and an uncontrolled cardiac dysrhythmia are also listed against it.

Activated charcoal is called the best of these methods. It is a highly adsorbent powder that adsorbs chemicals within minutes of contact and so prevents absorption and toxicity. The dose is 1 g/kg. It is likely to be beneficial if administered within 1 to 2 hours of ingestion of a toxic substance known to be adsorbed by it; traditionally this period is thought to be within one hour, while the toxin remains in the stomach, but the potential for benefit when it is administered later cannot be excluded. Dilute the appropriate amount in water or sorbitol and give it by lavage tube, or orally for an awake patient. In the gut lumen the charcoal adsorbs the poison and the charcoal-toxin complex is then evacuated with the stool. When the drug has an enterohepatic circulation, charcoal is readministered every 4 to 6 hours to limit reabsorption during recirculation. It should not be given for non-binding substances such as hydrocarbons, with an unprotected airway, at late presentation, when endoscopy is needed after a significant caustic ingestion because it impairs visibility, or with intestinal obstruction; the need for an oral antidote or for endoscopy is a relative contraindication.

Syrup of ipecac is for an alert conscious patient who has ingested a potentially toxic amount of a poison within the last one hour; the oral dose given is 30 ml in adults, 15 ml in children and 10 ml in small infants.

Cathartics increase the excretion of toxins from the gut, and the ones commonly used are magnesium sulphate, magnesium citrate and sorbitol. They have no definite indication.

Whole bowel irrigation is an option for potentially toxic ingestions of sustained release or enteric coated drugs. An isotonic solution of polyethylene glycol-electrolytes is given orally at 2 liters/hour in adults and 0.5 liters/hour in children, and continued for 4 to 6 hours or until the rectal effluent is clear. Bowel obstruction and ileus rule it out.