Tintinalli's Emergency Medicine - Just the Facts, 3ed.

116. METALS AND METALLOIDS

D. Adam Algren

LEAD

EPIDEMIOLOGY

images Lead is the most common chronic metal poisoning. Both ingestion and inhalation can result in clinical lead toxicity.

PATHOPHYSIOLOGY

images Lead toxicity results in injury to multiple organ systems but primarily involves the nervous, cardiovascular, hematologic, and renal systems.

images Central nervous system (CNS) neuronal injury results in cerebral edema and increased intracranial pressure. Lead toxicity may also produce peripheral neuropathies.

images Lead interferes with porphyrin metabolism and heme synthesis causing anemia.

CLINICAL FEATURES

images Table 116-1 lists the common signs and symptoms of lead poisoning by organ system.

TABLE 116-1 Common Manifestations of Lead Poisoning

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DIAGNOSIS AND DIFFERENTIAL

images Though an elevated serum lead level (>10 micrograms/dL) confirms the diagnosis, results are often not immediately available.

images Radiopaque material may be present in the gastrointestinal (GI) tract following acute ingestion. With chronic exposure, children may develop horizontal metaphyseal bands in long bones, especially involving the knee (“lead lines”).

images Other laboratory findings suggestive of lead poisoning include anemia with basophilic stippling of erythrocytes, hemolytic anemia, nephritis, and/or hepatitis.

EMERGENCY DEPARTMENT CARE AND DISPOSITION

images Consider whole-bowel irrigation with polyethylene glycol solution for lead ingestion, especially when radiopaque material is visible on a radiograph. The adult rate of instillation is 1500 to 2000 mL/h, and the pediatric rate of instillation is 500 to 1000 mL/h.

images Guidelines for chelation therapy are presented in Table 116-2.

images Patients requiring parenteral chelation therapy or whose only option is to return to the environment producing the lead exposure should be admitted to the hospital.

TABLE 116-2 Guidelines for Chelation Therapy in Lead-Poisoned Patients*

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ARSENIC

EPIDEMIOLOGY

images Arsenic is found in agricultural chemicals, insecticides, contaminated well water, and mining/smelting operations.

images Exposure to inorganic arsenic can result in significant toxicity whereas organic arsenic is minimally toxic.

PATHOPHYSIOLOGY

images Arsenic inhibits multiple enzymes and uncouples oxidative phosphorylation with effects on multiple organ systems.

CLINICAL FEATURES

images Clinical features of arsenic toxicity are summarized in Table 116-3.

images Chronic poisoning causes stocking glove peripheral neuropathies, hyperkeratosis, peripheral vascular disease, malaise, myalgia, abdominal pain, memory loss, and personality changes.

TABLE 116-3 Clinical Features of Arsenic Toxicity

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DIAGNOSIS AND DIFFERENTIAL

images Consider arsenic poisoning in patients with severe vomiting and diarrhea causing hypotension.

images Other diagnoses to consider include septic shock, encephalopathy, Guillain–Barre syndrome, Addison’s disease, hypo- and hyperthyroidism, porphyria, and other metal poisonings.

images Acutely, the electrocardiogram (ECG) may demonstrate a prolonged QT interval; abdominal radiographs may reveal radiopaque arsenic.

images Transverse white lines of the nails (Mees’ lines) may occur 4 to 6 weeks following ingestion.

images Definitive diagnosis depends on 24-hour urine arsenic levels.

EMERGENCY DEPARTMENT CARE AND DISPOSITION

images Treat hypotension with aggressive volume resuscitation with isotonic crystalloid, and vasopressors for fluid-refractory shock.

images Manage dysrhythmias according to Advanced Cardiac Life Support (ACLS) protocols, but avoid drugs that prolong the QT interval (class IA, IC, and III agents).

images Consider gastric lavage if the patient presents early following acute ingestion. Whole-bowel irrigation with polyethylene glycol solution is indicated for patients in whom abdominal radiographs demonstrate radiopaque material.

images Guidelines for inpatient chelation therapy with dimercaprol and outpatient treatment of stable patients with succimer are presented in Table 116-4.

images Hospitalization is recommended for patients with severe symptoms, those requiring parenteral chelation, and those with suicidal or homicidal intent.

TABLE 116-4 Guidelines for Chelation Therapy in Arsenic-Poisoned Patients

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MERCURY

EPIDEMIOLOGY

images Elemental mercury is present in older thermometers and exposures occur via inhalation, especially when vacuumed or heated. Ingestion of elemental mercury typically does not result in toxicity.

images Organic mercury is used in wood preservatives, fungicides, pesticides, and is also found in contaminated seafood. Absorption primarily occurs via the GI tract.

PATHOPHYSIOLOGY

images Similar to other heavy metals, mercury binds to sulfhydryl groups and affects multiple enzymes and organ systems.

CLINICAL FEATURES

images Inhalation of elemental mercury can result in fever, cough, dyspnea, vomiting, and headache that can progress to acute respiratory failure.

images Ingestion of inorganic mercury salts results in corrosive injury to the GI tract: vomiting, diarrhea, abdominal pain, and GI bleeding may occur. Acute renal failure often accompanies significant toxicity.

images Chronic inorganic mercury toxicity is associated with multiple neurologic effects including tremor, fatigue, depression, and headaches. Erethism refers the constellation of emotional lability, shyness, irritability, insomnia, and blushing. Acrodynia (“pink disease”) is characterized by a generalized rash, edema/erythema of the palms/soles, excessive sweating, fever, irritability, and muscle weakness.

images Organic mercury poisoning is usually seen with chronic ingestion and is associated with headache, tremor, fatigue, ataxia, blindness, muscle spasticity, and dementia.

DIAGNOSIS AND DIFFERENTIAL

images A history of exposure or physical findings of erethism or acrodynia may suggest the diagnosis.

images An elevated 24-hour urine mercury level confirms the diagnosis in cases of elemental and inorganic mercury exposures. An elevated whole blood mercury level is necessary to confirm poisoning from organic mercury compounds.

images The differential diagnosis of symptoms caused by mercury poisoning is extensive and includes other causes of encephalopathy, tremor, gastroenteritis, and acute renal failure.

EMERGENCY DEPARTMENT CARE AND DISPOSITION

images Supportive care and removal from exposure are the most important aspects in managing mercury poisoning. Intubation may be necessary in cases of respiratory failure associated with elemental mercury vapor exposure.

images Chelation is most effective in cases of elemental and inorganic mercury poisoning and should be considered in cases with significant symptoms (Table 116-5). Parenteral chelation is contraindicated in cases of organic mercury poisoning due to the potential to exacerbate CNS symptoms.

TABLE 116-5 Guidelines for Chelation Therapy in Mercury-Poisoned Patients

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For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 197, “Metals and Metalloids,” by Heather Long and Lewis S. Nelson.