Decontamination is commonly used in potentially poisoned animals in an attempt to remove the substance, reduce absorption and decrease the severity of poisoning. There are several methods that can be employed including emetics and gastric lavage for emptying the stomach and administration of adsorbents to reduce absorption. Dermal and ocular decontamination may also be required depending on the substance involved.
The choice of method will depend on the substance ingested, time since ingestion, the clinical condition of the animal, the availability of any drugs to be used and the experience of staff.
Dermal decontamination
Any animal that is exhibiting signs of cardiovascular collapse, respiratory distress, or profound neurological depression should be stabilised before decontamination is attempted. If dermal decontamination is to be delayed, collaring should be considered to prevent grooming and ingestion.
In most cases warm water and mild detergents (e.g. shampoo, washing up liquid) are suitable for dermal contaminants. In small patients it is important not to induce hypothermia with the use of cold water. If the substance is a dry powder, decontamination should start with brushing the coat before washing.
Contamination with oily, greasy substances or other substances that are not very water-soluble may require the use of a commercial degreaser such as Swarfega® (in the UK) or Goop (in the USA). Some degreasers contain beads or other insoluble substances to aid cleansing and removal of dirt and grease, but the products without these additions are most suitable for the decontamination of animals. It is important to note these degreasers are more effective if applied to dry fur as they may be water-soluble themselves. After application to the affected area the degreaser should then be thoroughly washed off, as some also contain a petroleum solvent. Other options for removal of sticky substances, such as glue traps or fly paper, are vegetable oil, margarine or butter (Bough, 2003; Wild, 2010). After decontamination these substances can then be washed off, although ingestion of a small quantity is not hazardous. Solvents such as alcohol or light petroleum products such as turpentine substitute (white spirit) are not recommended for dermal decontamination because they can spread the contaminant further and may also irritate the skin.
If there is heavy contamination or large clumps of material adhering to the fur, it may be more practical to clip decontaminated hair, particularly in longhaired animals.
It is important to ensure staff are adequately protected by the use of aprons, gloves and goggles (Bough, 2003). Aprons and gloves are recommended for substances that are a hazard from dermal exposure. Goggles should be used for decontamination of an animal exposed to a substance that can cause injury to the eyes if splashed. For some substances, such as strong smelling solvents or respiratory irritants, a mask may be needed and it will also be necessary to ensure decontamination is carried out in a well ventilated area. Remember that anything used to transport the animal (e.g. basket, blanket) may also be contaminated.
Corrosive substances, such as acids and particularly alkalis, can cause serious tissue damage. The chemicals are commonly available in oven cleaners and drain cleaners, although the chemicals themselves can also be purchased for household cleaning. Acids and alkalis on the skin should never be neutralised. The neutralisation reaction of an acid with an alkali or an alkali with an acid, produces heat and this can cause further tissue damage. Alkalis cause liquifactive necrosis with saponification of fats and solubilisation of proteins; they also absorb water from tissue. These effects result in adherence and deep penetration into the tissues. In contrast acids cause coagulative necrosis which can reduce further penetration of the acid and may protect deeper tissues, although in severe cases deep burns may occur.
Dermal exposure to strong alkalis (e.g. sodium hydroxide (caustic soda), potassium hydroxide) requires very thorough decontamination. These chemicals can cause deep penetrating burns which can be painless initially and progress over a few hours. Washing the contaminated area with water will only remove surface alkali and so repeated irrigation is required. After the initial decontamination and once the pH of the skin appears to be neutral (litmus paper or a urine dipstick can be used) it is necessary to wait 15 minutes. This allows residual alkali to diffuse up from the deeper regions of the dermis (Herbert and Lawrence, 1989; O'Donoghue et al, 1996). The pH of the area should then be checked again; if the skin has become strongly alkaline again, irrigation should be repeated. Decontamination should be repeated until the run-off fluid is no longer strongly alkaline. In some cases this can take several hours of repeated periods of decontamination. Some mildly alkaline substances such as detergents, can cause burns if left on the skin for a prolonged period.
Ocular decontamination
Ocular exposure is uncommon but can lead to severe corneal damage, depending on the chemical involved. Alkalis as explained above can cause particularly severe damage with deep corneal ulceration and damage to internal structures.
Ocular exposure should be managed promptly and as a first aid measure, owners can be advised to flush the eye with water prior to presentation. If only one eye is affected care should be taken to prevent contamination of the other during irrigation. On presentation particulate matter should be removed with cotton wool buds or forceps and contaminated eyes should be flushed with copious volumes of 0.9% saline or water for a minimum of 10–15 minutes. Sedation or anaesthesia may be required to facilitate decontamination. As with dermal exposure, no attempt should be made to neutralise acid or alkalis in the eye. With alkalis it is important to check the pH of the eye and to repeat the irrigation until a pH 8 or less is maintained (Osweiler et al, 2011).
After flushing the eye the corneal surface should be stained with fluorescein and examined carefully for ulceration. Mild corneal damage should be managed with ocular lubrication, topical antibiotics and parenteral analgesics as required. In the case of alkali exposure or severe corneal damage referral to a veterinary ophthalmologist may be required.
Gastrointestinal decontamination
Gastrointestinal decontamination is the most common method of decontamination used and it should be considered in all acute cases of ingestion of a poison and generally includes gastric evacuation (usually emesis or gastric lavage) and administration of an adsorbent. In some situations gastric evacuation is not required or recommended.
In most cases emptying the stomach is usually only worthwhile if ingestion was recent (i.e. within 1–2 hours) as the ingested material will have been absorbed or passed beyond the stomach. However, this is not always the case and some substances can remain in the stomach for longer (e.g. raisins and sultanas), so it may be necessary to seek advice in these cases. The physical form of the substance ingested (large tablets or a solution, for example) will also influence the time that ingested material remains available in the stomach. The chemical nature is also a factor; some substances are digested slowly but others (e.g. alcohol) are absorbed directly from the stomach.
Emesis
Emesis is the most common method of emptying the stomach in cats and dogs, but efficacy declines the longer the time between ingestion and emesis. Emesis is not always suitable depending on the substance ingested and the clinical condition of the animal (see Box 1). If the animal is very drowsy, seizuring or is unable to protect its airway, induction of emesis may lead to aspiration of the stomach contents. For some substances (e.g. aluminium or zinc phosphide, used as rodenticides in some countries) the vomitus may pose a hazard to staff due to the evaporation of a toxic substance (e.g. phosphine gas in the case of phosphide compounds) and induction of emesis in a well-ventilated area, preferably outside if practical, is recommended (AVMA, 2011).
A number of substances can be used for induction of emesis (Table 1). The choice will depend on the availability of drugs and agents and the species involved. Apomorphine is the emetic of choice in dogs and vomiting typically occurs within 1–20 minutes of administration (depending on how the apomorphine is administered). The intravenous route produces the most predictable and rapid response. It acts by stimulating dopamine receptors in the chemoreceptor trigger zone of the medulla but at high doses it causes central nervous system (CNS) depression and suppresses vomiting due to stimulation of opiate receptors within the vomiting centre of the brain. As a result repeated doses are unlikely to cause emesis because of the depressant effect of high doses on the vomiting centre, and are not recommended (Plumb, 2011). Induction of emesis may be ineffective in some cases because the substance ingested has an anti-emetic action (for example, cannabis, antihistamines).
| Apomorphine |
Dogs
|
| Xylazine |
Cats
|
| Washing soda (soda crystals, sodium carbonate) |
Cats and dogs
|
| Hydrogen peroxide 3% |
Cats and dogs
|
| Salt (sodium chloride) | Never to be used because of risk of hypernatraemia |
| Activated charcoal |
Cats and dogs
|
Note the choice will depend on the availability of drugs and agents. There are also variations in dosages and the substances used in different countries. See text for potential risks.
Induction of emesis in cats can be challenging. Apomorphine is generally not used. It may be less effective in cats compared with dogs and has been shown to cause behavioural changes, hallucinations and hypermania in cats (Trulson and Crisp, 1982; Motles et al, 1989). Alpha-2 adrenergic agonists (e.g. xylazine, medetomidine) can be used in cats as vomiting is an adverse (and therefore unreliable) effect of these drugs. Vomiting occurs more commonly with xylazine (Flaherty, 2013). Sedation is common but can be reversed with atipamezole.
Sodium carbonate (washing soda) crystals are an effective emetic in dogs and cats (BSAVA/VPIS, 2012) and are commonly used in the UK. However, administration can be a problem as washing soda is now more commonly available as a powder rather than crystals. In addition, it is essential that washing soda is not confused with caustic soda (sodium hydroxide). In a Veterinary Poisons Information Service (VPIS) case, massive swelling and severe oral burns and ulceration occurred in a dog given caustic soda instead of washing soda as an emetic. The dog was euthanised (VPIS case number 163548).
Hydrogen peroxide 3% is often recommended in the American literature as an emetic in dogs but it can cause local tissue damage with haematemesis and gastritis, particularly with overdosing in dogs or usage in cats. In addition, in the presence of organic matter hydrogen peroxide vigorously decomposes to oxygen and water and the oxygen produced can cause emboli, although this is more of a risk with higher concentrations (e.g. 30–40%), and has occurred in humans after ingestion of hydrogen peroxide (Cina et al, 1994).
In a review of 147 dogs given apomorphine or hydrogen peroxide as an emetic, vomiting occurred in 94% and 90% of dogs, respectively. Adverse effects occurred in 14% of dogs in both groups and included lethargy and persistent hypersalivation with apomorphine and diarrhoea, lethargy and protracted vomiting with hydrogen peroxide. The mean recovery of ingested material in this study was 48% for hydrogen peroxide and 52% for apomorphine (Khan et al, 2012). This is fairly typical where an emetic is expected to remove 40–60% of the stomach contents when vomiting occurs (Beasley, 1999).
A number of substances have been used as emetics in the past but they are obsolete and potentially dangerous. Salt (sodium chloride) should never be used. It can cause serious (Pouzet et al, 2007) or fatal (De Groot et al, 2008) hypernatraemia in animals when used as an emetic. Mustard is unreliable and not recommended (Beasley, 1999). Copper sulphate is also a potent emetic but is not recommended because of risk of toxicity. Syrup of ipecac (ipecacuanha) was widely used in the past but is now not routinely recommended. It is relatively ineffective, slow to act, has a bitter taste and is no longer widely available.
Gastric lavage
Gastric lavage is another method of gastric decontamination. It will only retrieve material from the stomach and is generally used in potentially severe cases of poisoning, particularly where there is rapid onset of signs and emesis is contraindicated (see Box 1).
Gastric lavage involves the passage of a tube via the mouth into the stomach followed by repeated administration and removal of small volumes of liquid to flush out the stomach contents. General anaesthesia is required and it is important to note that lavage will be ineffective if the material ingested is too large to pass up the tube used. Gastric lavage is contraindicated if the substance ingested is corrosive as gastric fluid can leak down the outside of the tube during the procedure resulting in damage to the oesophagus. In addition if the gut wall is damaged and weakened, placement of the tube could result in perforation. In smaller or younger animals it is important to maintain body temperature and to use warmed rather than cold water or saline as the lavage fluid. Once the procedure is complete activated charcoal can be left in the stomach, if appropriate.
Adsorbents
The most commonly used adsorbent is activated charcoal (Figure 1). It binds many toxic substances and further reduces gastrointestinal absorption. Activated charcoal is a finely powdered material that has been treated to give it a huge surface area (1000 m2/g), which is capable of binding a variety of drugs and chemicals. It is essential that activated charcoal is used to ensure the product has the maximum ability to adsorb toxicants. Slurries are more effective than tablets or capsules. The charcoal is not systemically absorbed or metabolised but passes through the gut. Activated charcoal is given as a single dose or in repeated doses and is given after emesis or gastric lavage. Timing of administration is important, as efficacy declines the longer the period is between ingestion and administration (AACT & EAPCCT, 2005). A single dose is most useful when the substance ingested is still in the stomach and in most cases that is all that is required. Repeat dose administration of activated charcoal is particularly important when the agent is enterohepatically recirculated (such as theobromine in chocolate) because it can interrupt enterohepatic recycling and/or promote drug exsorption from the systemic circulation into the gut lumen (Pond, 1986; McLuckie et al, 1990). Repeated doses of activated charcoal should only be given if the animal has normal bowel sounds. Note that activated charcoal does not bind everything and is not recommended for a number of substances (Box 2).
Activated charcoal will stain faeces black and if given in a sedated animal without airway protection can result in aspiration into the lungs and pneumonitis. Activated charcoal slows gut transit time, thus co-administration of a laxative (see below) can be considered. The use or timing of activated charcoal administration should be considered when oral treatments are to be used as the charcoal will also absorb these and will reduce their efficacy. A period of at least 2 hours should be allowed between administration of charcoal and oral medication.
Administration of activated charcoal may be difficult. Ideally it should be given alone as the adsorptive capacity may be reduced if mixed with other substances such as food. Activated charcoal is commonly given with dog or cat food to improve palatability and a recent in vitro study evaluated the effect of dog food on the adsorptive capacity of activated charcoal using paracetamol (acetaminophen) as a marker. A statistically significant reduction in the adsorptive capacity of activated charcoal was demonstrated with increasing amounts of dog food. However, all measurements of paracetamol represented a reduction in concentration of more than 98%. It was concluded that the addition of dog food to activated charcoal does reduce the total adsorptive capacity, but this reduction is unlikely to be clinically significant in the presence of both the formulation of dog food and the ratio of charcoal to dog food used in this study (1 g of charcoal to 2–14 g of dog food) (Wilson and Humm, 2013).
Laxatives (cathartics)
Laxatives (or cathartics) alone are ineffective as a method of gut decontamination (AACT & EAPCCT, 2004a). They can be used to increase the movement of substances, including absorbents, through the gut. Bulk laxatives can be used to reduce transit time of foreign bodies such as coins or batteries, although osmotic laxatives such as lactulose can also be used. Saline (e.g. magnesium sulphate) or saccharide cathartics (e.g. sorbitol) are sometimes given after activated charcoal to enhance elimination but only one dose should be given to reduce the risk of adverse effects (AACT & EAPCCT, 2004a). Mineral oil (liquid paraffin) is generally not recommended as a laxative because of the risk of aspiration.
Laxatives should not be used in animals with dehydration, diarrhoea, gastrointestinal obstruction or perforation, hypotension or electrolyte abnormalities. Electrolyte monitoring is required in animals receiving multiple doses of cathartics (due to the risk of hypernatraemia in animals receiving sodium-containing laxatives or hypermagnesaemia in those given a magnesium-containing laxative).
Whole bowel irrigation
Whole bowel irrigation is a method of decontamination used in human medicine. It is rarely used in the management of poisoning in veterinary medicine. It involves the administration of a polyethylene glycol-electrolyte bowel cleansing solution orally or by nasogastric tube until the rectal effluent resembles the irrigating solution (usually within 2–6 hours). It is most commonly used in human medicine for gut decontamination of body packers (individuals who smuggle drugs wrapped in plastic or other material) and patients who have ingested drugs which are poorly adsorbed by activated charcoal, particularly iron, or sustained release medications (AACT & EAPCCT, 2004b).
Conclusions
Decontamination in an animal with suspected poisoning is used to remove the substance, reduce absorption and decrease the severity of poisoning. In most cases warm water and a mild detergent is all that is required for effective dermal decontamination but some substances such as glues may require other removal agents. Alkalis on the skin or in the eye can cause serious tissue damage and may require repeated irrigation for effective decontamination. Emesis is the most common method of gastric decontamination although induction of emesis in cats remains a challenge. Use of emetics in contraindicated where there is risk of aspiration of stomach contents. Gastric lavage is generally reserved for potentially severe cases of poisoning, particularly where there is rapid onset of signs and emesis is contraindicated. Activated charcoal is a useful adsorbent but it is ineffective for a number of commonly ingested substances. The effectiveness of all methods of gastric decontamination declines as the period between ingestion and intervention increases.