Decontamination following overdose

This chapter refers to activated charcoal, gastric lavage, whole bowel irrigation, and basic strip-naked soap-and-water whole-body washing. There are siluations where all, or none, or some of these measures may be appropriate. Of the past paper questions, Question 29 from the second paper of 2010 asked for the greatest amount detail about the appropriate use of activated charcoal. Question 1b from the second paper of 2004 and  Question 5 from the first paper of 2002 ask about  the the role of decontamination in undifferentiated overdose ( eg. "found unconscious surrounded by empty pill packages"). Lastly, Question 15.4 from the second paper of 2012 expects the candidates to identify a bowel obstruction caused by a charcoal bezoar, with the history of carabamazepine overdose as the only clue that multi-dose charcoal has been administered. One might notice a fondness for activate charcoal in the minds of the examiners. Because of this, activated charcoal has been dedicated a chapter all of its own. If one were to read only one article about decontamination techniques,

In brief, decontamination can be critically evaluated in the following manner:

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.

Decontamination of the gut

Activated charcoal, in multiple or single doses

Induced emesis

• Ipecac is the traditional emetic (root extract of Cephalis ipecacuanha)
• The dose has used to be about 15-30ml of syrup and a glass of water.
• Clinical  studies  did  not  demonstrate  that  ipecac syrup  improved  patient  outcome.
• The side-effects are minimal, but there is probably no merit to this practice. Overdosed patients are unlikely to present with all the drug still in the stomach.
• Moreover, the regurgitation of corrosive material is going to do even more damage.
• Aspiration may result if vomiting is induced in a patient with a decreased level of consciousness
• The AACT/EAPCCT recommendation in 2004 was to abandon this practice.

Gastric lavage

• Historically, patients who could not be compelled to drink ipecac (by virtue of being unconscious) were subjected to nasogastric tube insertion and gastric lavage.
• Content which has moved beyond the stomach is inaccessible to lavage.
• Research which had previously supported the use of gastric lavage has been based on the removal of marker substances, rather than on patient outcomes. One author was amazed by the lack of any actual evidence in support of this practice ("it is quite remarkable that gastric lavage survived the scrutiny of clinical scientists for so long"- Krenzelok, 2002)
• Furthermore, lavage cannot be used together with activated charcoal.

Cathartics and charcoal

• Traditionally, charcoal was mixed with sorbitol, an osmotic laxative.
• This was to improve the taste of charcoal, and to speed its transit through the gut to prevent "desorption" of drug from the charcoal particles.
• Again, this practice has no merit.

Whole bowel irrigation

• Large amounts  of  iso-osmotic  polyethylene  glycol  solution is given until the effluent runs clear.
• Clarity of effluent is taken as a sign that the bowel has been "decontaminated". Obviously,  this is not valid - it cannot be said that the bowel has been completely cleansed of all toxin just because the effluent has turned clear.
• It has a role to play only in a few specific scenarios:
  • Iron overdose
  • Sustained-released drugs
  • Enteric-coated drugs
  • Swallowed drug packages (i.e. contraband)

Surgical and endoscopic decontamination

• In certain situations, surgical removal of the toxic material is not only possible but desirable. These situations include:
  • Massive bezoars of any sort, causing obstruction
  • Iron tablets
  • "Body packing" - contraband concealed for transport by swallowing

Decontamination of the surface area

• Most overdoses are by ingestion; but some may be by contact exposure
• Drugs which absorb readily though the skin include the following:
  • Glycerol ethers
  • Industrial solvents, eg. carbon tetrachloride, trichloroethylene, methylene chloride, etc.
  • Mercury salts
  • Lead salts
• Many more can be found in this publication, based on the 2005 TLV (Threshold Limit Values) Booklet by the American Conference of Governmental Industrial Hygienists (ACGIH) as having a “potential significant contribution to the overall exposure by the cutaneous route, including mucous membranes and the eyes, either by contact with vapors, or, of probable greater significance, by direct skin contact with the substance.”
• Decontamination of the exposed skin surface follows the same principle as gut decontamination (i.e. prevent absorption).
• Specific topical antidotes may also exist, eg. calcium for hydrofluoric acid