Toxicologic decontamination (Proceedings)

General concepts:

The goal of decontamination is to prevent the continued absorption of the toxicant. Owners and staff should be advised to protect themselves from toxic exposure when decontaminating a patient; this principle is particularly true with dermal toxins and toxins that are easily volatilized.

Toxicity

Exposure assessment should always be attempted to estimate the dose compared to the known toxicity of the compound. If the dose approaches the toxic range then vigorous decontamination procedures are justified.

Type of substance

Various chemical of physical properties of individual toxins may indicate or preclude particular decontamination techniques. Examples of such restrictions would be the high risk of aspiration pneumonia following emesis after ingestion of volatile hydrocarbons.

Time since exposure

This is a critical factor. Many studies have exhibited a significant decrease in recovery of toxins with a variety of decontamination techniques as the time from exposure increases.

Species affected

Species differences in both physiology and anatomy often necessitate changes in decontamination techniques used for a similar toxin. Some species for example do not vomit and trying to lavage a rumen is difficult due to the volume involved.

Underlying disease

Some decontamination techniques require stresses both on the animal and various organ systems which would preclude their use in animals with preexisting pathology in those organ systems. An example would be attempting urine alkalization in a patient with underlying renal disease.

Routes of exposure and decontamination methods

Topical:

Ocular

Ocular exposures require copious flushing with water or physiologic saline. Flushing should continue for a minimum of 15 minutes, and sedation maybe necessary in some patients. Multiple flushings are often necessary.

Dermal

Dermal exposures allow for both transdermal absorption and oral exposure as the animal tries to clean itself. Rubber gloves and plastic aprons should be used by all decontaminating personnel. Victims with long hair coats may benefit from having the hair clipped before cleaning the skin. Mild soaps will remove most toxins, but multiple washings maybe necessary. Try to minimize trauma to the skin which could enhance absorption of the toxin. Oily substances can often be removed with commercial mechanics hand degreasing agents such as GOJO and or GOOP. These degreasers then need to be washed off to prevent the subsequent ingestion by the patient. Monitor the patient to prevent hypothermia, aspiration or ingestion of the toxin, soap or combination of both.

Particularly difficult dermal decontaminations involve acid or caustic substances with the resultant dermal burns. These require gentle washing with copious volumes of tepid water and mild soaps, trying to minimize trauma.

Gastrointestinal:

Gastric evacuation

Emesis

The following is the position paper for ipecac syrup in humans but is applicable to apomorphine or other emetics. *"Syrup of ipecac should not be administered routinely in the management of poisoned patients. In experimental studies the amount of marker removed by ipecac was highly variable and diminished with time. There is no evidence from clinical studies that ipecac improves the outcome of poisoned patients and its routine administration in the emergency department should be abandoned. There are insufficient data to support or exclude ipecac administration soon after poison ingestion. Ipecac may delay the administration of reduce the effectiveness of activated charcoal, oral antidotes, and whole bowel irrigation. Ipecac should not be administered to a patient who has a decreased level or impending loss of consciousness or who has ingested a corrosive substance or hydrocarbon with high aspiration potential".

Gastric lavage

*"Gastric lavage should not be employed routinely, if ever, in the management of poisoned patients. In experimental studies, the amount of marker removed by gastric lavage was highly variable and diminished with time. The results of clinical outcome studies in overdose patients are weighed heavily on the side of showing a lack of beneficial effect".

Absorbents

Activated charcoal

Single dose activated charcoal

*"Single dose activated charcoal should not be administered routinely in the management of poisoned patients. Based upon volunteer studies, the administration of activated charcoal may be considered if a patient has ingested a potentially toxic amount of a poison (which is known to be absorbed to charcoal) up to one hour previously. Although volunteer studies demonstrate that the reduction of drug absorption decreases to values of questionable clinical importance when charcoal is administered at times greater than one hour, the potential for benefit after one hour cannot be excluded. There is no evidence that the administration of activated charcoal improves clinical outcome. Unless a patient has an intact or protected airway, the administration of charcoal is contraindicated".

Multiple dose activated charcoal

*"Although many studies in animals and volunteers have demonstrated that multiple-dose activated charcoal increases drug elimination significantly, this therapy has not yet been shown in a controlled study in poisoned patients to reduce morbidity and mortality. Further studies are required to establish its role and the optimal dosage regimen of charcoal to be administered. Based on experimental and clinical studies, multiple-dose activated charcoal should be considered only if a patient has ingested a life-threatening amount of carbamazepine, dapsone, Phenobarbital, quinine, or theophylline. With all of these drugs there are data to confirm enhanced elimination, though no controlled studies have demonstrated clinical benefit. Although volunteer studies have demonstrated that multiple-dose activated charcoal increases the elimination of amitriptyline, dextropropoxyphene, digitoxin, digtoxin, disopyramide, nadolol, phenylbutazone, phenytoin, piroxicam, and sotalol, there are insufficient clinical data to support or exclude the use of this therapy. The use of multiple-dose activated charcoal in salicylate poisoning is controversial. Data in poisoned patients are insufficient presently to recommend the use of multiple-dose charcoal therapy for salicylate poisoning. Unless a patient has an intact or protected airway, the administration of multiple-dose activated charcoal is contraindicated. It should not be used in the presence of an intestinal obstruction".

Cathartics

*"The administration of a cathartic alone has no role in the management of the poisoned patient and is not recommended as a method of gut decontamination. Experimental data are conflicting regarding the use of cathartics in combination with activated charcoal. No clinical studies have been published to investigate the ability of a cathartic, with or without activated charcoal, to reduce the bioavailability of drugs or to improve the outcome of poisoned patients. Based upon available data, the routine use of a cathartic in combination with activated charcoal is not endorsed. If a cathartic is used, it should be limited to a single dose in order to minimize adverse effects of the cathartic."

Whole bowel irrigation

*"Whole bowel irrigation (WBI) should not be used routinely in the management of the poisoned patient. Although some volunteer studies have shown substantial decreases in the bioavailability of ingested drugs, no controlled clinical studies have been performed and there is no conclusive evidence that WBI improves the outcome of the poisoned patient. Based upon volunteer studies, WBI should be considered for potentially toxic ingestions of sustained-release or enteric-coated drugs particularly for those patients presenting greater than two hours after drug ingestion. WBI should be considered for patients who have ingested substantial amounts of iron as the morbidity is high and there is a lack of other options for gastrointestinal decontamination".

Manual removal

Endoscopy

Surgery

Toxicants which are refractory to other decontamination techniques may need to be manually removed. An example would be iron tables which will adhere to the gastric lining.

Enhanced elimination

Activated charcoal (multiple dose) [see above]

Forced diuresis

Forced diuresis is used when the toxicant has a high level of renal excretion. The object is to increase urine flow rates to 3 to 5ml/kg/hr to force renal clearance of the toxicant. The administration of diuretics and fluid overload in combination are used to achieve this goal.

Urine alkalinization

*"The term urine alkalinization emphasizes that urine pH manipulation rather than a diuresis is the prime objective of treatment; the terms forced alkaline diuresis and alkaline diuresis should therefore be discontinued. Urine alkalinization increases the urine elimination of chlorpropamide, 2,4-dichlorophenoxyacetic acid, diflunisal, fluoride, mecoprop, methotrexate, Phenobarbital, and salicylate. Based upon volunteer and clinical studies, urine alkalinization should be considered as a first line treatment for patients with moderately severe salicylate poisoning who do not meet the criteria for hemodialysis. Urine alkalinization and high urine flow (approximately 600ml/hour) should also be considered in patients with severe 2,4-dichlorophenoxyacetic acid and mecoprop poisoning. Administration of bicarbonate to alkalinize the urine results in alkalemia (an increase in blood pH or reduction in its hydrogen ion concentration); pH values approaching 7.70 have been recorded. Hypokalemia is the most common complication but can be corrected by giving potassium supplements. Alkalotic tetany occurs occasionally, but hypocalcemia is rare. There is no evidence to suggest that relatively short-duration alkalemia (more than a few hours) poses a risk to life in normal individuals or in those with coronary and cerebral arterial disease".

Peritoneal dialysis

The goal of peritoneal dialysis is to speed the elimination of water-soluble, low molecular weight, poorly protein bound toxicants which have a limited volume of distribution. This technique has been demonstrated to be to inefficient (to slow) to be clinically helpful and other faster procedures will accomplish the same goal.

Hemodialysis (charcoal hemoperfusion)

Hemoperfusion is not routinely employed in the veterinary setting, while effective in cleansing the blood of toxicants it raises significant technical challenges for the general veterinary practice.

Antidotes: it is important to be aware of the half life (t1/2) of both the toxicant and antidote since some antidotes will clear the body before the toxicant has been eliminated.

*This position paper was prepared using the methodology agreed by the American Academy of Clinical Toxicology (AACT) and the European Association of Poisons Centres and Clinical Toxicologist (EAPCCT). All relevant scientific literature was identified and reviewed critically by acknowledged experts using set criteria. Well-conducted clinical and experimental studies were given precedence over anecdotal case reports and abstracts were not considered. The position paper was subjected to detailed peer review by an international group of clinical toxicologist chosen by the AACT and EAPCCT, and a final draft was approved by the boards of the two societies.