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

103. ANTICHOLINERGICS

O. John Ma

EPIDEMIOLOGY

images Anticholinergic toxicity is encountered because of the common use of phenothiazines, mydriatics, skeletal muscle relaxants, antihistamines (particularly diphenhydramine), antidepressants, antispasmotics, and antiparkinsonian drugs.

images Jimsonweed is a plant associated with anticholinergic toxicity.

PATHOPHYSIOLOGY

images The mechanism of action involves cholinergic blockade of muscarinic receptors (primarily in the brain), nicotinic receptors, or both. The clinical effects of these agents result from disturbances in the parasym-pathetic nervous system (peripheral effects) and the brain (central effects).

images Drug absorption can occur after ingestion, smoking, or ocular use.

images Table 103-1 describes muscarinic and antimuscarinic effects.

TABLE 103-1 Muscarinic and Antimuscarinic Effects

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CLINICAL EFFECTS

images Clinical findings include mydriasis, hypoactive or absent bowel sounds, tachycardia, flushed skin, disorientation, urinary retention, hyperthermia, dry skin and mucus membranes, dysarthria, confusion, agitation, and auditory or visual hallucinations.

images Clinical findings can be remembered as: Dry as a Bone, Red as a Beet, Hot as a Hare, Blind as a Bat, Mad as a Hatter, and Stuffed as a Pipe.

images The most common ECG finding is sinus tachycardia. Wide-complex tachydysrhythmias and QT-interval prolongation can also be seen.

DIAGNOSIS AND DIFFERENTIAL

images Diagnosis is primarily clinical. In isolated anticholinergic toxicity, routine laboratory studies should be normal. Nonetheless, obtain electrolytes, glucose level, toxicology screening, and pulse oximetry in the presence of altered mental status.

images In contrast, sympathomimetic toxicity and delirium tremens present with moist skin and active bowel sounds. Acute psychiatric disorders may have tachycardia and tachypnea, but the physical examination is otherwise unremarkable.

images The differential diagnosis includes viral encephalitis, Reye’s syndrome, head trauma, other intoxications, neuroleptic malignant syndrome, alcohol withdrawal, delirium tremens, acute psychiatric disorders, and sympathomimetic toxicity.

EMERGENCY DEPARTMENT CARE AND DISPOSITION

images Treatment is primarily supportive. Place the patient on a cardiac monitor and secure intravenous access.

images GI decontamination with activated charcoal may be useful even outside the 1-hour window of ingestion because of diminished GI motility.

images Treat hyperthermia and seizures with conventional measures.

images Standard antiarrhythmics are usually effective, but class la medications should be avoided. Treat wide complex tachydysrhythmias with intravenous sodium bicarbonate.

images Treat agitation with benzodiazepines, such as lorazepam. Phenothiazines should be avoided.

images Physostigmine treatment is controversial. Consider its use if conventional therapy fails to control agitation and delirium. The initial dose is 0.5 to 2 milligrams IV, administered slowly over 5 minutes. When effective, a significant decrease in agitation may be apparent within 15 to 20 minutes.

images Physostigmine may lead to severe bradycardia and asystole. It is contraindicated in patients with asthma, intestinal or bladder obstruction, or heart block.

images Discharge patients with mild anticholinergic toxicity after 6 hours of observation if their symptoms have resolved. Admit more symptomatic patients for 24 hours of observation. Patients receiving physostigmine usually require at least a 24-hour admission.


For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 196, “Anticholinergics,” by Paul M. Wax and Amy C. Young.