CHAPTER 109

Management of poisoning

Poisoning is defined as a pathologic state caused by a toxic agent. Sources of poisoning include medications, plants, environmental pollutants, and drugs of abuse. These toxicants may enter the body orally or by injection, inhalation, or absorption through the skin. Poisoning may be unintentional (accidental) or intentional. Symptoms of poisoning often mimic those of disease, and hence the possibility of poisoning should be considered whenever a diagnosis is made.

In the United States, over 2.4 million poisonings are reported annually. In 2005, accidental poisoning caused 23,618 deaths, and intentional poisoning caused 5833 more. Most poisoning deaths are caused by drugs: In 2004, 95% of deaths from accidental poisoning were caused by drugs, as were 75% of suicides. The incidence of poisoning is highest in young children. However, the mortality rate in this group is very low. In 2000, poisoning-related medical expenses were $26 billion.

Fundamentals of treatment

Poisoning is a medical emergency and requires rapid treatment. Management has five basic elements: (1) supportive care, (2) identification of the poison, (3) prevention of further absorption, (4) poison removal, and (5) use of specific antidotes. These essentials are discussed below.

Supportive care

Supportive care is the most important element in managing acute poisoning. Support is based on the clinical status and requires no knowledge specific to the poison involved. Maintenance of respiration and circulation are primary concerns. Measures for respiratory support include inserting an airway, giving humidified oxygen, and providing mechanical ventilation. Volume depletion (resulting from vomiting, diarrhea, or sweating) can compromise circulation. Volume should be restored by administering normal saline or Ringer’s solution. Severe hypoglycemia may occur, resulting in coma. Levels of blood glucose should be monitored. For coma of unknown etiology, IV dextrose should be given immediately—even if information on blood glucose is lacking. Acid-base disturbances may occur; determination of arterial blood gases will facilitate diagnosis and management. If convulsions develop, IV diazepam is the treatment of choice.

Poison identification

Treatment of poisoning is facilitated by knowing the identity and dosage of the toxicant. Efforts to obtain this information should proceed concurrently with medical management.

A history is one way to identify the toxic agent. However, experience has shown that histories taken at times of poisoning are often inaccurate. Hence, statements about the nature or quantity of poison may not be correct.

Positive identification can be made using analytic techniques. A gas chromatograph/mass spectrometer can provide qualitative and quantitative information. Analyses can be performed on specimens of urine, blood, and gastric contents. To determine whether poison levels are rising or falling, analyses should be performed on sequential blood samples taken about 2 hours apart.

Prevention of further absorption

By reducing the absorption of a poison, we can minimize blood levels, and thereby significantly decrease morbidity and mortality. For ingested poisons, three procedures are available: (1) giving activated charcoal, (2) gastric lavage and aspiration, (3) and whole-bowel irrigation. Induction of emesis with syrup of ipecac, either at home or in the clinic, is no longer recommended. When poison exposure is topical, surface decontamination is employed. Details of these procedures are discussed in the following section.

Promotion of poison removal

Measures that help eliminate poison from the body shorten the duration of exposure and, if implemented before plasma levels have peaked, can reduce the maximum level of poison achieved. By shortening exposure and reducing maximum poison levels, these measures can decrease morbidity and mortality.

Removal of poison can be promoted with drugs and with nonpharmacologic techniques. The drugs used for poison removal act by increasing renal excretion of toxic agents. Nonpharmacologic methods of poison removal include peritoneal dialysis, hemodialysis, and exchange transfusion. Details on methods of poison removal are presented later.

Use of specific antidotes

An antidote is an agent administered to counteract the effects of a poison. Examples include naloxone (to reverse poisoning by heroin and other opioids) and physostigmine (to treat poisoning by atropine and other anticholinergic drugs). Several specific antidotes are discussed later. Unfortunately, although antidotes can be extremely valuable, these agents are rare: For most poisons, no specific antidote exists. Hence, for most patients, treatment is limited to the general measures described above.

Drugs and procedures used to minimize poison absorption

Reducing absorption of ingested poisons

Activated charcoal

Treatment with activated charcoal is a preferred method for removing ingested poisons from the GI tract. Activated charcoal is an inert substance that adsorbs drugs and other chemicals. Binding of toxicants to charcoal is essentially irreversible. Because charcoal particles cannot be absorbed into the blood, adsorption of poisons onto charcoal prevents toxicity. The charcoal-poison complex is eliminated in the stool. Patients should be advised that charcoal will turn the feces black. Charcoal is very safe, but should not be used in patients with bowel perforation or obstruction.

Charcoal selectively adsorbs large molecules that contain a carbon atom. Adsorption of small molecules and molecules that lack a carbon atom is poor. Among these poorly absorbed molecules are heavy metals, caustics and corrosives, alcohols and glycols, chlorine, iodine, and petroleum distillates.

Because charcoal can adsorb antidotes, and thereby neutralize their benefits, antidotes should not be administered immediately before, with, or shortly after the charcoal.

Activated charcoal has the consistency of a fine powder and is mixed with water for oral administration. The adult dose is 60 to 100 gm. Pediatric doses range from 15 to 30 gm. For poisoning with certain compounds—phenobarbital, dapsone, quinidine, theophylline, and carbamazepine—giving sequential doses of charcoal can be beneficial. When administered within 30 minutes after poison ingestion, charcoal can adsorb about 90% of the dose. However, if given 60 minutes after poison ingestion, the amount adsorbed decreases to only 37%. Clearly, charcoal should be given as soon as possible after poison exposure.

Gastric lavage and aspiration

Gastric lavage (irrigation) and aspiration consists of flushing the stomach with fluid and then sucking (aspirating) the fluid back out. The procedure should be done only in life-threatening cases, and only if less than 60 minutes has elapsed since poison ingestion. Specific contraindications to lavage and aspiration include

• Ingestion of caustic agents (owing to the risk of esophageal perforation)

• Convulsions (owing to the risk of injury from the procedure, including aspiration of stomach contents into the lungs)

• Ingestion of high-viscosity petroleum distillates

• Significant cardiac dysrhythmias

• Emesis of blood

Lavage and aspiration is accomplished using a large-bore orogastric tube (No. 36 to 42 French for adults, No. 22 to 28 French for children). Smaller tubes should be avoided because they may not permit removal of solids (food, pills, capsules, tablets) and because their small diameter would impede flow of the lavage fluid. If the patient is comatose, an endotracheal tube with an inflatable cuff should be installed to protect the airway. Because of the anatomy of the stomach, the patient should be placed on the left side with the head down. Prior to initiation of lavage, stomach contents should be aspirated and sent for toxicologic analysis. Lavage may be performed employing tap water or saline solution. Multiple washes are instilled using 150 to 200 mL/wash (for adults and older children) or 50 to 100 mL/wash (for children under 5 years old). Larger volumes should be avoided since they may push stomach contents into the small intestine. Washes should be repeated until the fluid retrieved from the stomach is clear. About 10 to 12 washes are employed.

Whole-bowel irrigation

Whole-bowel irrigation is done with a solution of polyethylene glycol that contains balanced electrolytes, available under the trade names CoLyte and GoLYTELY. The solution is administered repeatedly over a 5-hour period, either by mouth or through a nasogastric tube. Rates of administration are as follows:

• For patients age 12 years and older—1.5 to 2 L/hr

• For patients 6 to 12 years old—1 L/hr

• For patients less than 6 years old—0.5 L/hr

The procedure has been effective following ingestion of iron, lithium, and lead, as well as sustained-release products. Whole-bowel irrigation should not be used in patients with ileus, peritonitis, bloody vomitus, or obstruction or perforation of the bowel.

Surface decontamination

Topical exposure to toxicants can cause local and systemic injury. To minimize injury, contaminated clothing should be removed, and the poison should be washed from the victim. The recommended procedure is to alternate soap-and-water washes with alcohol washes. Personnel performing these washes should take precautions to avoid contaminating themselves. If the victim’s eyes have been exposed, they should be flushed with water for at least 15 minutes. Shampoo should be employed to remove toxic agents from the hair and scalp.

Drugs and procedures used for poison removal

Drugs that enhance renal excretion

Drugs that alter the pH of urine can accelerate the excretion of organic acids and bases. Agents that elevate urinary pH (ie, make the urine more alkaline) will promote the excretion of acids. Drugs that lower urinary pH will promote the excretion of bases. The mechanism underlying these effects is called ion trapping (see Chapter 4).

The drugs employed most frequently to alter urinary pH are sodium bicarbonate and ammonium chloride. Both are administered IV. Sodium bicarbonate renders the urine more alkaline, which decreases the passive reabsorption of acids (eg, aspirin, phenobarbital), and thereby accelerates their excretion. Ammonium chloride acidifies the urine, and thereby increases the excretion of bases (eg, amphetamines, phencyclidine). Because of the buffer systems present in blood, sodium bicarbonate and ammonium chloride have a relatively small effect on the pH of blood, while having a large effect on the pH of urine.

Nondrug methods of poison removal

Several nondrug procedures—peritoneal dialysis, hemodialysis, hemoperfusion, and exchange transfusion—can be employed to remove toxicants from the body. Although these procedures are usually of limited value, they can be lifesaving in some situations. Nondrug procedures are most effective when (1) binding of toxicants to plasma proteins is low, and (2) blood levels of toxicants are high (ie, when distribution of the toxic agent is restricted to the blood and extracellular fluid).

Each of the nondrug methods of poison removal has its benefits and drawbacks. Peritoneal dialysis has two advantages: the procedure is relatively simple and it occupies a minimum of staff time. Hemodialysis, although more difficult than peritoneal dialysis, is about 20 times more effective. Hemoperfusion is a process in which blood is passed over a column of charcoal or absorbent resin. If the affinity of the resin for a particular poison is high, the procedure can strip a toxicant from binding sites on plasma proteins. The principal disadvantage of hemoperfusion is loss of platelets. When binding of a poison to plasma proteins is particularly avid, exchange transfusion can be an effective method of removal.

Specific antidotes

Heavy metal antagonists

The heavy metals most frequently responsible for poisoning are iron, lead, mercury, arsenic, gold, and copper. These metals cause injury by forming complexes with enzymes and other physiologically important molecules. Poisoning may result from environmental exposure, intentional overdose, or therapeutic use of heavy metals.

The drugs given to treat heavy metal poisoning are called chelating agents or chelators. These agents interact with metals to form chelates—ring structures in which the metal and the chelating agent form two or more points of attachment. The chelate formed by mercury and dimercaprol illustrates this concept (Fig. 109–1).

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