Management of common household toxins (Proceedings)

• The initial approach to the poisoned patient includes major organ system assessment and stabilization.

• Gastric evacuation can be achieved by induction of emesis, gastric lavage, or whole bowel irrigation.

• Activated charcoal is an adsorbent that binds toxins and facilitates excretion through the gastrointestinal tract.

• Cathartics often are used in combination with activated charcoal and decrease the absorption of toxins by shortening gastrointestinal transit time.

• Other methods exist to enhance elimination of toxins but are not widely recommended because of their potential harmful effects or limited availability.

Key therapeutic points

Immediate assessment of the patient should be performed to evaluate vital signs and major body systems. Appropriate therapy should be initiated to stabilize the cardiovascular, respiratory, and neurologic systems. In the event of a witnessed ingestion, it may be appropriate to administer an antidote immediately. However, in many cases an antidote does not exist or the exact toxic agent is not known. Therefore, when treating the poisoned patient, decontamination often becomes the most effective means of therapy. Depending on the route of exposure, several methods of decontamination may be used to eliminate the toxin and prevent continued absorption. Further symptomatic and supportive care should be tailored to the needs of the individual patient.

Gastrointestinal decontamination is used to limit exposure to ingested toxins and traditionally has consisted of gastric emptying followed by the administration of agents to hasten toxin elimination. Methods of gastric evacuation include emesis induction and gastric lavage. Following gastric evacuation, activated charcoal may be administered to adsorb residual toxin. Cathartics such as sorbitol are commonly used in conjunction with activated charcoal to shorten gastrointestinal transit time and hasten elimination of ingested toxins.

Emesis

Emetics act either locally to cause gastric irritation or centrally at the chemoreceptor trigger zone to induce vomiting. A number of factors should be considered before inducing emesis including time of ingestion, agent ingested, and clinical status of the patient. Most emetics are effective only if given within 1 to 2 hours of ingestion, and induction of emesis does not eliminate the need for additional therapies, because emetics are successful at retrieving only a fraction of the gastric contents. Emesis is contraindicated with ingestion of petroleum distillates, corrosive agents, or sharp objects because of the risk of aspiration and damage to the esophagus. Emesis should not be induced in animals with altered mentation or seizures because of the possibility of aspiration, in animals that are already vomiting, and in animals with preexisting health conditions such as significant cardiac disease, epilepsy, or recent abdominal surgery.

Hydrogen peroxide administered orally is used frequently to induce vomiting in cats and dogs. Because of its availability and low cost, hydrogen peroxide is often recommended to pet owners for use at home to promote rapid removal of ingested toxins. The dosage is 1 to 2 ml/kg, (not to exceed 3 tbsp even in large dogs), administered with a syringe or turkey baster. Administration of hydrogen peroxide results in vomiting by triggering gastric irritation and is usually effective within minutes. The dose may be repeated once if emesis is not achieved. The use of more concentrated or higher doses of hydrogen peroxide is not advised, because it may lead to severe vomiting, mucosal irritation or ulceration, and salivation.

Apomorphine hydrochloride is a synthetic opiate that stimulates dopamine receptors in the chemoreceptor trigger zone to induce vomiting. Apomorphine is considered by many veterinarians to be the emetic of choice in dogs, but its use in cats is unreliable. The recommended dosage in dogs is 0.03-0.04 mg/kg intravenously or intramuscularly. Apomorphine may also be administered conjunctivally by crushing a portion of a tablet (approximately 0.25 mg/kg) and dissolving it in a few drops of water. The conjunctival sac is then rinsed after emesis has occurred to prevent ongoing vomiting. Adverse effects associated with apomorphine include protracted vomiting, restlessness, excitement, and central nervous system depression. Naloxone may be used to the reverse the central nervous system depression but does not inhibit the emetic effects.

Another emetic that can be used is xylazine hydrochloride, an α2-adrenergic agonist. The recommended dosage for emesis in cats is 0.44 to 1.1 mg/kg administered intramuscularly or subcutaneously. Adverse effects include sedation, bradycardia, arrhythmias, and muscle tremors. Once emesis has been achieved, the effects of the drug can be reversed with yohimbine hydrochloride at a dosage of 0.25 to 0.5 mg/kg intramuscularly. Xylazine does not reliably produce emesis in dogs.

The administration of syrup of ipecac, liquid dishwashing detergents, and table salt (sodium chloride) are not recommended. Syrup of ipecac has a narrow therapeutic index in dogs and safer options are available. Excessive quantities of salt may result in hypernatremia and seizures. Attempts by pet owners to "gag" their pets are also unreliable and may be dangerous to both the patient and the pet owner.

Gastric lavage

Gastric lavage may be indicated when emesis has failed, when emesis is contraindicated (depressed mental state, loss of gag reflex), or when administration of charcoal is critical and emesis would delay its administration. Contraindications to gastric lavage include ingestion of hydrocarbons because of high aspiration potential, ingestion of corrosive substances, and risk of hemorrhage or gastrointestinal perforation resulting from pathology or recent surgery. As with induction of emesis, the effectiveness of this procedure is dependent on the time of ingestion and is likely to be most effective within the first 1 to 2 hours postintoxication.

In the conscious animal, gastric lavage is performed after induction of general anesthesia with the patient intubated to prevent aspiration. The cuff of the endotracheal tube should be assessed before initiation of gastric lavage to ensure a snug fit. The patient is positioned in lateral recumbency with the head lower than the thorax. A large-bore gastric tube with a fenestrated end is placed alongside the patient and the distance measured from the tip of the nose to the last rib. The fenestrated end of the tube may then be lubricated and gently passed down the esophagus into the stomach to the marked distance on the tube. Tube placement may be confirmed by aspiration of gastric contents, air insufflation with a stethoscope placed over the stomach, or by radiographic confirmation. Warm water or saline is infused into the tube, with approximately 5 to 10 ml/kg per cycle to moderately distend the stomach. The fluid is then allowed to drain from the tube via gravity flow. The procedure is repeated until clear fluid is returned. Activated charcoal may then be administered through the tube. The end of the tube should be occluded before removal to prevent spillage of tube contents into the pharynx.

Activated charcoal

Activated charcoal is available in the form of granules, tablets, capsules, or as a suspension. The suspension may also be obtained in combination with a cathartic such as sorbitol. In human patients the suspension is significantly more effective than the tablets or capsules.

The recommended dosage of activated charcoal is 1 to 4 gm/kg administered by syringe. Pets exhibiting no clinical symptoms may drink the charcoal freely. A small amount of food may be added to the solution to enhance palatability. In animals exhibiting clinical symptoms, charcoal may be administered through an orogastric tube with a cuffed endotracheal tube in place to protect against aspiration. Another useful technique, especially in cats, is administration of the charcoal through a nasogastric tube. Tube placement should always be confirmed before administration.

As with most decontamination procedures, activated charcoal is most effective if given soon after toxin ingestion. In the human literature, it has been shown that administration is most effective within 1 hour of toxin ingestion. However, the potential for benefit beyond 1 hour cannot be excluded. Multiple doses of activated charcoal may be appropriate when managing toxins that undergo enterohepatic circulation or with drugs that diffuse into the intestinal tract from the systemic circulation down their concentration gradients. In these situations charcoal is repeated every 4 to 8 hours and may be beneficial for several days. In human patients, substantial decreases in serum half-life with the use of multidose activated charcoal have been reported for theophylline, phenobarbital, digitoxin, dapsone, and antidepressants.

When other methods of decontamination such as emesis induction or gastric lavage are employed, charcoal administration may be delayed. Human studies have questioned the need for gastric emptying procedures before administration of activated charcoal, and several have shown that charcoal alone is as effective as gastric emptying and charcoal combined. Further studies in animals are currently underway at Michigan State University to determine the effectiveness of charcoal alone in the management of acute poisoning.

Cathartics

Cathartics such as sorbitol decrease the absorption of substances by accelerating their expulsion from the gastrointestinal tract. Cathartics often are administered with charcoal to hasten toxin elimination from the gastrointestinal tract before absorption. If multiple doses of activated charcoal are given, a cathartic should be used only with the first dose of charcoal to prevent diarrhea and dehydration. Cathartics are contraindicated in cases of recent abdominal trauma, recent bowel surgery, intestinal obstruction or perforation, or with ingestion of a corrosive substance.

Enhanced elimination

Other methods that have been used to enhance the elimination of certain toxins and drugs from the body include diuresis, ion trapping, hemodialysis, and hemoperfusion. Forced diuresis using large volumes of intravenous fluids may be effective for toxins that are eliminated primarily through the kidneys. However, this management carries some risk of volume overload with resulting pulmonary and cerebral edema. Therefore as a general principle this technique should be avoided unless specifically indicated by the nature of the toxin ingested. Manipulation of urine pH with alkalinizing or acidifying agents has been proposed to trap substances in the ionized form and enhance elimination. However, the agents used to accomplish these goals may induce a systemic alkalosis or acidosis that may be more detrimental to the patient than the toxin itself. Therefore, this therapy as a general management should be avoided. Hemodialysis and hemoperfusion are techniques that allow blood to be removed from the body, filtered through a membrane or an adsorbent material, and then returned to the patient. These techniques are highly effective for certain toxins, but are unfortunately not widely available in veterinary practice.

Supportive care

The goals of therapy in any toxicologic emergency should include prevention of further toxin absorption, administration of appropriate antidotes when applicable, and supportive care. Many toxins or their metabolic byproducts have the potential to cause secondary organ damage beyond the initial insult. Therefore, in addition to general decontamination procedures and specific antidotes, intoxicated patients may require further symptom-targeted treatments and supportive care. These include maintenance of respiratory and cardiovascular function, control of acid–base disorders, maintenance of body temperature, and control of central nervous system disorders. Regardless of the toxin ingested, a problem-oriented approach should always be employed to determine the most effective and appropriate therapies for each individual patient.

If unsure about the management of a specific toxin, The ASPCA Animal Poison Control Center should be contacted at (888) 426-4435. This service provides detailed information about assessment and management of specific toxins for a cost of $60.

References/Suggested Reading

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Corby DG, Lisciandro RC, Lehman RH, et al: The efficiency of methods used to evacuate the stomach after acute ingestions. Pediatrics 40(5):871-874, 1967

Yeary RA: Syrup of ipecac as an emetic in the cat. J Am Vet Med Assoc 161(12):1677-1678, 1972

American Academy of Clinical Toxicology/European Association of Poison Control Centres and Clinical Toxicologists: Position paper: ipecac syrup. J Toxicol Clin Toxicol 42(2):133-143, 2004

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American Academy of Clinical Toxicology/European Association of Poison Control Centres and Clinical Toxicologists: Position paper: gastric lavage. J Toxicol Clin Toxicol 42(7):933-43, 2004

Seger D: Single-dose activated charcoal-backup and reassess. J Toxicol Clin Toxicol 42(1):101-111, 2004

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Green R, Grierson R, Sitar DS, et al: How long after drug ingestion is activated charcoal still effective? J Toxicol Clin Toxicol 39(6):601-605, 2001

Christophersen AB, Levin D, Hoegberg LG, et al: Activated charcoal alone or after gastric lavage: a simulated large paracetamol intoxication. Br J Clin Pharmacol 53(3):312-317, 2002

American Academy of Clinical Toxicology/European Association of Poison Control Centres and Clinical Toxicologists: Position paper: single-dose activated charcoal. J Toxicol Clin Toxicol 43(2):61-87, 2005

American Academy of Clinical Toxicology/European Association of Poison Control Centres and Clinical Toxicologists: Position paper: cathartics. J Toxicol Clin Toxicol 42(3):243-254, 2004