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Chapter: Modern Medical Toxicology: Chemical Poisons: Heavy Metals

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Lead - Chemical Poisons: Treatment

Severe acute poisoning with encephalopathy: This is amedical emergency and the following measures must be undertaken immediately

Treatment

Severe acute poisoning with encephalopathy: This is amedical emergency and the following measures must be undertaken immediately –

BAL 4 mg/kg immediately (in children).

Cranial CT scan: to rule out cerebral oedema.

–– If there is cerebral oedema, it can be managed by the following measures:

-- Controlled hyperventilation, maintaining an arterial CO2 tension of 25 to 30 mmHg, can reduce intracranial pressure in patients with rapidly worsening mental status, lateralising neurologic findings or evidence of impending herniation. Prolonged hyperventilation is not desirable in general. Monitor intracranial pres-sure continuously. Monitor cardiovascular function, renal function, and serum electrolytes carefully.

--  Diuretics

»»  Mannitol 20%:Adult:1 to 1.5 gm/kg by infusion over 10 to 20 minutes. Child: 0.5 to 1 gm/kg by IV infusion over 10 to 20 minutes.

»» Glycerol: 0.3 to 1 gm/kg orally.

»» Loop Diuretics: Furosemide and/or ethacrynic acid may be useful as an adjunct in the treatment of cerebral oedema.

»» Corticosteroids:

⌂⌂ Dexamethasone—low dose - 16 mg/day in divided doses.

⌂⌂ Dexamethasone—high dose— 1 to 2 mg/kg/day in divided doses.

·              KUB: to rule out lead chips in GI tract.

·              For seizures: Treat seizures with intravenous diazepam (Adult: up to 10 mg slowly, repeat if necessary;

Children: 0.1 to 0.3 mg/kg slowly). Seizures from leadencephalopathy may be resistant to anticonvulsant therapy; barbiturate coma and aggressive control of ICP may be needed.

·              Foley catheterisation: to monitor urinary specificic gravity, sediment, lead level.

·              CaNa2 EDTA 75 mg/kg/day IV infusion.

·              After the initial dose of BAL, repeat the same dose at 4 hourly intervals until blood lead level falls below 40 mcg/100 ml. Then reduce BAL to 12 mg/kg/day in 3 divided doses.

·              Reduce CaNa2 EDTA to 50 mg/kg/day as condition improves.

–– Continue the above regimen until patient is asymptomatic and can tolerate oral chelation with D-penicillamine or DMSA.

Severe acute poisoning without encephalopathy: (BL morethan 70 mcg/100 ml) –

·              BAL 12 mg/kg/day.

·              EDTA 50 mg/kg/day.

·              Discontinue BAL when the BL falls below 40 mcg/100 ml, but continue EDTA for 5 more days.

·              Change to oral chelation subsequently which may have to be continued until the BL falls below 15 mcg/100 ml, or 3 months have been completed.

Moderate poisoning: (BL between 45 and 70 mcg/100 ml) –

·              EDTA 50 mg/kg/day.

·              When blood lead falls below 40 mcg/100 ml, begin oral chelation.

Mild poisoning: (BL between 20 and 35 mcg/100 ml) –

·              D-Penicillamine 30 mg/kg/day in 3 divided doses. Start with ¼th of the calculated dose. Double this after 1 week. Double again (to full dose) after 1 week. Continue this until the BL falls to less than 15 mcg/100 ml, or 3 months have been completed.

·              In addition to the above protocol, the following supportive measures must be instituted as applicable –

·              Thiamine 10 to 50 mg/kg is said to improve neurological

·              In acute poisoning, or in the event of radiopacities in the GI tract on x-ray, stomach wash can be done.

·              Lead colic usually responds to IV calcium gluconate.

·              Correct iron deficiency if present.*

·              IV fluids, (maintain specific gravity of urine under 1020).

·              If intracranial pressure is high due to cerebral oedema, administer mannitol or steroids as required (vide supra). Organic lead poisoning is mainly managed symptomatically. Chelation is done only if there is production of inorganic lead in the body from organic lead.

·              After one round of chelation therapy, allow an interval of 2 weeks and then esimate the BL. Repeat chelation if neces- sary. Rebounds are common. And finally the sine qua non of treament of heavy metal poisoning: remove the patient from the source of exposure. In recent times, a new chelating agent called Succimer has been introduced in the management of lead poisoning in Western countries. It is said to be more efficacious and less toxic.

Treatment guidelines for children:

·              BL less than 10 mcg/100 ml—Re-evaluate and rescreen patients in 1 year. No additional action required.

·              BL 10–19 mcg/100 ml—Lead education and referrals should be provided. If the result of screening test is 10–14 mcg/100 ml, perform diagnostic test for lead on venous blood within 3 months, and at least one follow-up test within 3 months. If the result of screening test is 15–19 mcg/100 ml, perform diagnostic test for lead on venous blood within 2 months, and at least one follow-up test within 2 months. Follow according to guidelines in 20–44 mcg/100 ml range if BL persists in 15–19 mcg/100 ml range.

·              BL 20–44 mcg/100 ml—Lead education and referrals should be provided. Provide clinical evaluation and management. If the result of screening test is 20–29 mcg/100 ml, perform diagnostic test for lead on venous blood within 1 month. If the result of screening test is 30–44 mcg/100 ml, perform diagnostic test for lead on venous blood within 1 week. Follow-up testing should be performed every 1 to 2 months.

·              BL 45–69 mcg/100 ml—Lead education and refer-rals should be provided. Provide coordination of care (case management) within 48 hours. Perform clinical evaluation and management within 48 hours. Provide diagnostic testing within 24–48 hours and follow-up testing (in accordance with chelation therapy, at least once a month).

·              BL equal to or greather than 70 mcg/100 ml - A medical emergency. Hospitalise the patient and begin immediate chelation therapy.

Occupational exposure:

·              Employees whose blood lead level is equal to or greater than 50 mcg/100 ml should be temporarily removed from exposure until their blood lead level is at or below 40 mcg/100 ml.

·              Employees may also be removed from exposure for medical reasons even if their blood lead levels are within 40 mcg/100 ml.

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