CHAPTER 124: Toxicology in Adults

KEY POINTS

General Measures

• Supportive measures supersede other considerations in the management of the poisoned patient. After addressing the ABCDs of life support, the focus can switch to confirmation of intoxication and targeted therapy.

• Administer a “cocktail” of oxygen, dextrose, thiamine, and naloxone to patients with depressed mental status.

• An increase in anion gap, osmol gap, or arterial saturation gap should raise the suspicion of intoxication.

• An osmol gap of large magnitude (>25 mOsm/kg) suggests methanol or ethylene glycol poisoning; however, serious intoxication with either agent can occur without increasing the osmol gap, particularly in the later stages of intoxication.

• Carbon monoxide and methemoglobin elevate the arterial oxygen saturation gap. These toxins interfere with oxygen binding to hemoglobin and decrease oxygen content without lowering $PaO2$. Oxygen saturation measured by pulse oximetry is falsely high in this setting.

• Toxicology screening can provide direct evidence of intoxication, but it rarely impacts initial management.

• Poison control center consultation is advised to determine appropriate laboratory testing and patient disposition and treatment. The emergency phone number is 1-800-222-1222.

• Gastric lavage only improves outcome in patients if performed within 1 hour of ingestion, although this time may be extended in poisonings that delay gastric emptying. Risks of lavage preclude its use in nontoxic ingestions, subtoxic amounts of a toxic ingestion, ingestion of caustic liquids, and when the toxin is no longer expected to be in the stomach. The airway must be protected prior to lavage.

• Activated charcoal should be administered for most acute oral ingestions if the airway is protected.

• Whole-bowel irrigation with a polyethylene glycol electrolyte solution is only indicated for iron overdose, ingestion of sustained-release tablets, and “body packing” with illicit drugs.

• Urinary alkalinization enhances excretion of nonpolar weak acids and is most commonly used in salicylate toxicity.

Acetaminophen

• All overdose cases should be screened for acetaminophen poisoning.

• The antidote, N-acetylcysteine (NAC), should be started within 8 hours of ingestion to decrease the risk of hepatotoxicity. The Rumack-Matthew nomogram allows for stratification of selected patients into categories of probable, possible, and no hepatic toxicity.

Alcohols

• Metabolic acidosis with an elevated anion gap and/or the presence of an osmol gap are classic in methanol and ethylene glycol poisoning.

• Features of methanol poisoning include inebriation, optic papillitis, and pancreatitis.

• Features of ethylene glycol poisoning include inebriation, acute renal failure, crystalluria, and myocardial dysfunction.

• Treatment of methanol and ethylene glycol poisoning with fomepizole or ethanol inhibits metabolism by alcohol dehydrogenase to toxic metabolites. Dialytic removal of toxic metabolites is indicated in severe poisonings.

• Isopropanol causes hemorrhagic gastritis, ketonemia, and ketonuria, but not acidosis. Fomepizole and ethanol are not indicated because metabolites are nontoxic. Dialysis is effective in severe cases.

Barbiturates

• Hypothermia, hypotension, bradycardia, flaccidity, hyporeflexia, coma, and apnea are features of barbiturate overdose. Severe overdose can mimic death.

• Supportive measures include gastric emptying and activated ...