College Answer

(b)       What is the role of decontamination of the digestive tract?

The role of decontamination of the digestive tract is controversial. This does not refer to Selective Decontamination of the Digestive tract (SDD) which is a form of antimicrobial prophylaxis. The induction of emesis is not favoured. The routine use of gastric lavage and/or activated charcoal has lost favour in the majority of overdose situations because of the limited evidence of benefit, and the possibility of harm (eg. aspiration or trauma). There are some situations where either or both of these techniques should be considered: early presentation (eg. < 1 hour) or presence of a drug which would delay gastric emptying, and presence of toxic drug in high quantities (eg. lethal dose) especially if in a slow release form. Administration of charcoal does not absorb small highly ionised chemicals (eg. metals, electrolytes, acids and alkali). Additional techniques such as repeated activated charcoal (and/or cathartics eg. sorbitol) or whole bowel irrigation (eg. with polyethylene glycol balanced electrolyte solution) may be considered (especially with slow release preparations). Rarely is surgical removal required.

Discussion

b)

Rationale for decontamination

• In any overdose, especially early, there is some proportion of the ingested drug which still has not absorbed.
• This unabsorbed drug could potentially be cleared from the gut
• This would result in a reduced total dose of the drug
• The reduced total dose should also result in a reduced total toxicity
• Ergo, the removal of undissolved drugs should reduce the toxicity of the overdose

Techniques of decontamination and their indications

• Activated charcoal, single or multiple doses
• Induced emesis (abandoned)
• Gastric lavage (largely abandoned; only indicated within the first hour)
• Whole bowel irrigation (only indicated for iron and slow release enteric coated tablets)
• Surface decontamination for skin-absorbed toxins

Situations which merit the use of gut decontamination

• The overdose is recent (within the last hour)
• There is reason to believe a large number of undissolved tablets is still present in the stomach or gut
• There is no adequate antidote to the drug, and the overdose is lifethreatening

Criticsm of gut decontamination techniques

• Possibility of aspiration is ever-present, particularly if the airway is unprotected
• Likelihood of effect diminishes with time.
• Even charcoal may have serious complications, eg. bowel obstruction
• Many of the early studies which lauded the effectiveness of gut decontamination techniques such as emesis or lavage were focused on the effectiveness of the emetic in achieving emesis, or in the lavage recovery of some abstract marker substance. No studies focused on patient outcome. Patient outcomes do not seem affected by decontamination techniques.
• The removal of a proportion of ingested drug may have no effect on the course of the overdose, in terms of outcome. One may think of this in terms of the difference between absorbing 100g of paracetamol vs. only absorbing 75g. In either case, your liver is screwed.