Chapter 8 Toxicological Decontamination
This chapter explores multiple decontamination procedures. Other chapters in this text cover the use of specific antidotes, supportive care, and emergency management of the poisoned patient. 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. An important rule in toxicological decontamination is not to contaminate the decontaminators. The aim of successful decontamination is to inhibit or cease further toxin absorption and enhance elimination from the body.
Contaminated eyes should be flushed with copious quantities of water or physiological saline. The eyes should be flushed for a minimum of 15 minutes; often multiple flushings are required. Mild sedation or a short-acting anesthetic may be necessary to control the patient before flushing. As a first-aid measure, owners should be advised to flush contaminated eyes at least 15 minutes before transporting the patient to the veterinary facility for complete evaluation and specific medical intervention.
As already mentioned, it is paramount for the veterinarian and paraprofessional staff to protect themselves from dermal exposure when transporting or decontaminating the dermally exposed patient. Rubber gloves and aprons should be used by the attending staff. Toxic dermal exposures allow both transdermal absorption and oral exposure if the patient tries to clean itself by licking.
Long-haired patients may benefit from having the hair clipped before cleaning the skin. Washing with a mild soap or detergent usually removes most toxins. Several washings may be required. Oily substances can often be removed with commercial hand-cleaning degreaser compounds, such as Gojo or Goop. These compounds themselves may be toxic if ingested and should be removed by washing with warm water and soap. Hypothermia is possible, and the patient’s overall physical status should be continually evaluated while decontamination procedures are ongoing.
Special care is necessary when decontaminating acid and caustic burns. Toxin-exposed skin should be copiously flushed with tepid water. The damaged tissue is easily traumatized, and extreme care should be taken not to add mechanical injury to the wound when removing the toxin from the skin.
The effectiveness of vomiting and the percentage of the gastric contents recovered depends on several factors. These factors include the physical properties of the toxin ingested, the time elapsed from toxin ingestion to induction of emesis, the volume of gastric contents, and the emetic agent used.
Emesis is contraindicated when the risk of aspirating vomitus is great. This includes situations in which the patient is stuporous, neurologically depressed, or is unconscious or at risk of becoming so before the emetic can work. Additionally, if the animal is having seizures or is at serious risk of a seizure before the emetic works, the risk of aspiration is increased. No emetic should be employed when oil, gasoline, or other petroleum distillates have been ingested. Emesis is contraindicated if vomiting will reexpose the mouth, pharynx, larynx, or esophagus to additional injury from ingested caustic or corrosive compounds.
Studies have indicated that the more rapidly emesis is induced, the greater the percentage of recovery of gastric contents.1–4 In one study in dogs, the maximum toxin recovery reported was 75% (range, 9% to 75%) with a mean recovery of 49% when emesis was induced within 11 to 30 minutes after toxin ingestion.1 Generally, gastric recovery in dogs ranges from 17% to 62% if emesis is induced within 60 minutes after toxin ingestion.1–4 In humans, mean toxin recovery achieved by emesis induction ranged from 21% to 60%.5,6 In all these studies, the emetic was administered within 60 minutes after toxin ingestion.
Emesis has been successful in removing toxins when it is administered longer than 1 hour postingestion; however, it should be stressed that the volume recovered decreases significantly as time passes. Inducing vomiting more than 4 hours after toxin ingestion is generally of little value.
The usefulness of emetics also depends on the toxic compound ingested. If the toxin has strong antiemetic activity, emetics may be ineffective. As a general rule, if a specific emetic fails to induce vomiting after two doses, it will not be effective. For example, apomorphine, a potent emetic, works by stimulating the chemoreceptor trigger zone. However, it also directly depresses the emetic center, so if the initial dose fails to induce emesis, subsequent doses are not likely to be effective. Additionally, emetics themselves can be toxic if normal dosages are exceeded.
Emetics are usually classified into two groups—those used by the owner at home as a form of first aid and those used by the veterinarian in the medical facility. Home-use emetics include 7% ipecac syrup, 3% hydrogen peroxide (H2O2), liquid dishwashing detergent, and table salt (NaCl). Veterinary emetics include apomorphine and xylazine.
A comment on home induction of emesis: I do not routinely advise home induction of emesis. Often the time spent by the owner finding the emetic and then catching and trying to dose the animal usually consumes more time than it would take to drive promptly to the veterinary facility. Generally, home-administered emetics usually succeed only in delaying prompt medical evaluation and specific therapeutic intervention. Additionally, home emetics may not be as successful as clinically available compounds. Owners often miscalculate the weight of the animal and can be either too passive or too aggressive in calculating the dose and administering the compound. The toxin ingested may cause mental depression before the home-administered emetic takes effect, leaving the patient with no airway protection. The risk of aspiration and other secondary side effects of available home emetics is significant. Generally, most owners can transport the animal to a veterinary facility within 30 to 45 minutes. Often the best first aid is rapid transport of the patient and toxin container to the nearest veterinary facility, where prompt induction of emesis is possible.
This compound is derived from the dried root of Cephaelis ipecacuanha, which is indigenous to South America. The active alkaloids are emetine and cephaeline. This product should not be confused with ipecac fluid extract, which is 14 times stronger. Outdated products can be used, but may be less effective. The mechanism involved is direct gastric irritation and stimulation of the chemoreceptor trigger zone. The dosage for dogs is 1 to 2 mL/kg orally; the dosage for cats is 3.3 mL/kg. Some recommend that the cumulative dosage should not exceed 15 mL in either species. The dose can be repeated once. Effective vomiting should result within 10 to 30 minutes, although it can be delayed for up to an hour.
Problems with syrup of ipecac include difficulty in administering the compound to conscious patients because of its bitter taste, which is particularly repugnant to cats. Also, a lack of effectiveness in inducing emesis in 50% of small animal patients has been observed. Additionally, if the patient fails to vomit, the ipecac should be removed from the stomach by lavage because of its potential cardiotoxic arrhythmia-inducing action. In humans the most common complications related to ipecac administration are diarrhea, lethargy, depression, and prolonged vomiting.
Hydrogen peroxide is most effective if it is administered after a small meal. Recommended dosage in dogs and cats is 1 to 5 mL/kg orally, generally not to exceed 50 mL for dogs (although many veterinarians exceed this total dose with negligible complications reported) or 10 mL for cats. The mechanism of action is believed to be gastric irritation. There are no significant risks from H2O2 ingestion. However, the owner should be careful to prevent the patient from aspirating the hydrogen peroxide when it is being administered. If it is successful, 3% hydrogen peroxide usually induces emesis within 10 minutes. If it is unsuccessful, the dose can be repeated.
The recommended dosage in dogs and cats is 1 to 3 tsp orally. Sodium chloride acts as a direct gastric irritant. It usually induces emesis within 10 to 15 minutes. Several negative sequelae are possible with administration of sodium chloride, including hypernatremia, particularly in young animals if emesis is not induced. Additionally, hematemesis can occur. In children oral sodium chloride administration has produced hypernatremia, cerebral edema, and convulsions. If emesis induction is unsuccessful, lavage should be considered to remove the excess salt. If emesis is successful, water should be available ad lib. The use of table salt as an emetic in companion animals is generally discouraged because of the potential for inducing more harm than good.
The recommended oral dosage in dogs and cats is 10 mL/kg body weight of a mixture of 3 tbsp detergent to 8 oz of water. Vomiting usually results within 20 minutes after administration. Detergents containing phosphate are most effective. The mechanism of action is primarily gastric irritation. In one human trial, liquid dishwashing detergent appeared to be safe, and emesis was initiated in 83% of patients compared with 97% of controls given ipecac.7 The effectiveness of liquid detergent in the veterinary population has not been fully elucidated. These detergents should not be confused with caustic detergents, such as electric dishwasher soap or laundry detergent, which are alkaline and are extremely caustic and could induce serious injury to the upper gastrointestinal tract.
One advantage of “veterinary emetics” is the possibility of using them in conjunction with activated charcoal. Once emesis has been induced, the emetic can be readministered after the patient has received a dose of activated charcoal.
Apomorphine acts directly on the chemoreceptor trigger zone to induce emesis. Apomorphine is generally the emetic of choice because of its rapid onset and the ability to reverse its action. Apomorphine is given at a dose of 0.02 to 0.04 mg/kg intravenously or intramuscularly. It can also be administered by placing it directly behind the eyelid in the subconjunctival sac. Diluting the pill with sterile water minimizes ocular irritation. Apomorphine solutions are not stable and must be made fresh before each administration. Vomiting usually ensues within 4 to 6 minutes. When used conjunctivally, the eye should be flushed copiously once vomiting occurs. Apomorphine can be used in cats but at the lower end of the dosage, and adverse side effects can be reversed with naloxone (0.01 to 0.04 mg/kg IV) in both dogs and cats. Apomorphine administered subcutaneously often has a delayed onset of action, and the duration of action may be prolonged.
Apomorphine can induce central nervous system (CNS) excitability in patients intoxicated with snail bait (metaldehyde), and its use in these patients is not recommended. Apomorphine may also be contraindicated when further CNS depression will significantly alter the patient’s condition. Adverse side effects include CNS and respiratory depression, excessive vomiting, and occasionally CNS stimulation.
Xylazine can be used as an emetic in cats with limited effectiveness at a dosage of 0.5 to 1 mg/kg IM or subcutaneously (SC). Xylazine has centrally acting α2-agonist activity. If effective, this drug usually induces vomiting within 10 minutes. The major adverse effect of xylazine is respiratory depression. The activity of this drug can be reversed with yohimbine, an α2-antagonist, at a dosage of 0.1 mg/kg IV in both dogs and cats.
The purpose of gastric lavage is to remove ingested toxins from the stomach by irrigation. The procedure may be indicated if emesis induction is ineffective or contraindicated. The patient must be unconscious or lightly anesthetized, placed in right lateral recumbency. A cuffed endotracheal tube must be in place. A large stomach tube is passed into the stomach no farther caudal than the xiphoid process. The patient is placed in an inclined position with the head down at approximately a 20-degree angle. If the patient is tilted at too great an angle, the weight of the fluid-filled stomach on the diaphragm can impair respiration.
Water or physiologic saline is then instilled by gravity flow at a volume of 10 mL/kg body weight. Physiologic saline is the lavage fluid of choice in smaller patients, which are more prone to fluid and electrolyte abnormalities. Care should be taken to prevent overdistention of the stomach. The degree of gastric distention can be felt by placing a hand on the abdomen. Lavage fluid should be warm to slow gastric emptying and prevent hypothermia of the patient. Manual agitation of the stomach is performed while the lavage fluid is aspirated, and the procedure is repeated until the recovered lavage fluid is clear. Often a bilge or stomach pump is employed to churn the stomach contents and aid in recovering the lavage fluid. Copious amounts of lavage fluid are usually required (often 15 to 20 lavage cycles), and the practitioner should be prepared for disposal of the same volume. The fluid initially recovered should be saved for toxicological examination. An activated charcoal suspension can be instilled before the stomach tube is removed.
An increasing trend is to administer activated charcoal before performing lavage to halt further absorption of the toxin. Removal of the toxin-charcoal complex becomes the goal of gastric lavage. Additional activated charcoal is then instilled after the lavage procedure has been completed.
Several studies of lavage have been performed in animals, and none has demonstrated substantial drug recovery, particularly if the procedure was delayed for more than 60 minutes after ingestion of the toxin.1–3 When lavage was performed within 15 to 20 minutes of toxin ingestion, the mean recoveries were 38% and 29%, respectively. If lavage was delayed until 60 minutes after ingestion of the marker, the mean recoveries were 13% and 8.6%. In the majority of poisoned patients that present to the veterinary hospital nearly 60 minutes have already passed since toxin ingestion, and by the time the mechanics of setting up a lavage procedure are performed and lavage is started, this time period has clearly passed. Therefore, the practical clinical success of this decontamination procedure is questionable.
It seems prudent to employ this technique if the ingested material is chunky, and large fragments of material can be expected to be recovered. However, chunky material larger than the diameter of the stomach tube will obviously not be retrieved. Additionally, lavage may be more effective in combating ingestions of toxins that delay gastric emptying, such as salicylates, anticholinergics, and cyclic antidepressants. Concretions may not be recovered. Other examples of anticipated poor recovery are toxins similar to iron tablets, which may adhere to the gastric lining, or large amounts of chocolate, which may melt into a significant ball of material that is difficult to retrieve.
The major complications of gastric lavage are aspiration pneumonia, laryngospasm, hypoxia, hypercapnia, fluid and electrolyte imbalances, and mechanical injury to the throat, esophagus, and stomach. Gastric lavage is contraindicated in patients with an unprotected airway, with ingestions of substances that carry a high risk of aspiration (e.g., hydrocarbons) or that are corrosive, with ingestion of sharp objects, with an underlying pathological condition that increases the risk of hemorrhage or gastric perforation, and in patients that are postsurgical or have medical conditions that may be compromised by the lavage procedure.
Another version of this technique is enterogastric lavage. This entails gastric lavage combined with retrograde high enema. This technique requires placing a gastric tube and endotracheal tube and then instilling an enema solution until it passes from the stomach tube.