Toxicological Decontamination

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.





GASTROINTESTINAL DECONTAMINATION



Emesis


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.14 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.14 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.



Home-use emetics







Veterinary emetics


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.





Gastric lavage


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.13 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.

Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on Toxicological Decontamination
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