General Toxicology and Toxidromes

Chapter 78 General Toxicology and Toxidromes



Aaron B. Skolnik, MD , Susan R. Wilcox, MD




1 What are the most common causes of death by poisoning?


In order from most to least commonly reported, the following categories of drugs are the 10 associated with toxin-related fatalities:



image Miscellaneous sedatives


image Miscellaneous hypnotics


image Miscellaneous antipsychotics


image Miscellaneous cardiovascular drugs


image Opioids


image Acetaminophen combinations


image Acetaminophen alone


image Miscellaneous antidepressants


image Miscellaneous stimulants and street drugs


image Miscellaneous muscle relaxants and cyclic antidepressants



2 What are the common toxidromes?


Toxidromes are syndromes associated with particular classes of toxins. They may be useful in making the diagnosis of poisoning and initiating treatment as patients are often too ill to wait for the results of laboratory or other testing (Table 78-1).


Table 78-1 Toxidromes



































Toxidrome Clinical findings Example agents
Cholinergic Diarrhea, fecal incontinence, enuresis, miosis, tachycardia followed by bradycardia, lacrimation, sialorrhea, sweating, muscle fasciculations followed by weakness and/or paralysis, altered mental status Organophosphate and carbamate insecticides
Amanita muscaria
Nicotine
Anticholinergic Agitated delirium, flushing, decreased sweating, tachycardia, mydriasis, urinary retention, decreased peristalsis, hyperthermia Atropine
Benztropine
Scopolamine
Diphenhydramine
Sympathomimetic Mydriasis, hyperthermia, seizures, hyperactivity, hypertension, tachycardia, diaphoresis, delusions, piloerection Cocaine
Methamphetamine
MDMA
Sympatholytic Miosis, hypotension, bradycardia or reflex tachycardia, CNS depression Clonidine
Methyldopa
Oxymetazoline
Opioid Miosis, CNS depression, respiratory depression or apnea, may have hypotension Heroin
Morphine
Fentanyl
Oxycodone
Serotonin syndrome Mental status changes, autonomic hyperactivity, neuromuscular abnormalities, akathisia, tremor, clonus, muscle hypertonicity, hyperthermia Sertraline
Fluoxetine
Citalopram
Linezolid
Trazodone
Meperidine
Tramadol
Neuroleptic malignant syndrome Fever, “lead pipe” muscular rigidity, altered mental status, autonomic dysfunction (in setting of recent treatment with neuroleptics) Haloperidol
Chlorpromazine
Promethazine
Prochlorperazine
Ziprasidone
Quetiapine

CNS, Central nervous system; MDMA, methylenedioxymethamphetamine.



3 What laboratory testing is indicated in the poisoned patient?


Laboratory testing in critically ill poisoned patients should be dictated by the suspected toxin(s) and the findings of the history and physical examination. Laboratory testing should include serum electrolytes and calculation of the anion gap. If the anion gap is elevated, serum osmolarity and calculation of the osmolar gap are often useful. Further laboratory testing might include transaminase and prothrombin time (PT) for a patient who has ingested acetaminophen. Arterial blood gas testing is useful in a critically ill patient poisoned by salicylates as is a carboxyhemoglobin level in a patient with carbon monoxide exposure. Urinalysis may show oxalate crystals suggesting ethylene glycol poisoning or may even fluoresce under a Wood lamp if a patient has ingested a commercial antifreeze preparation.



4 What is the value of serum and urine toxicology screens in the poisoned patient?


In many hospitals, a basic serum toxicology screen includes levels of acetaminophen, salicylate, and volatile alcohols. This is a good starting point when ingestants are unknown as it includes treatable toxins for which serum levels guide therapy. Quantitative levels of tricyclic antidepressants are of no value in determining treatment, and many hospitals use a qualitative screen. Urine drug screens are often used to test for metabolites of drugs of abuse and are often not valuable in making a toxicologic diagnosis. Some hospitals have comprehensive blood or urine toxicology testing that can isolate many obscure compounds. However, the results of these tests often become available long after the window for appropriate treatment has closed for patients. It is important to know the availability of toxicologic testing at your hospital and to be aware of the limitations of testing. Cross-reactivity with particular assays may also lead to false positives. Treating patients on the basis of their clinical status rather than their test results is often the safest plan.



5 What other diagnostic testing is useful in the poisoned patient?


Electrocardiography is a noninvasive test that rapidly supplies a great deal of information about a number of potential toxins and has prognostic value in cyclic antidepressant and sodium channel blocker poisoning. It is sound practice to obtain at least one electrocardiogram in all poisoned patients. Chest radiography should be obtained if a patient has significant pulmonary symptoms or findings or requires airway management.



6 What is the role of gastric lavage in the management of the poisoned ICU patient?


Usually, there is no role for gastric lavage (stomach pumping) in the critically poisoned patient. Gastric lavage involves the passage of a large-bore orogastric tube and the repeated instillation and aspiration of fluid to remove potentially toxic stomach contents. In animal and volunteer studies, the recovery of drugs is highly variable and declines quickly as the time from ingestion increases. Clinical studies have not confirmed a benefit of gastric lavage alone even when performed rapidly (<60 minutes) after ingestion. Given that significant time typically elapses before arrival of a poisoned patient in the intensive care unit (ICU), gastric lavage in the ICU is likely to be of no benefit. In addition, orogastric lavage has been associated with complications including aspiration, hypoxia, hypercapnia, electrolyte disturbances, and mechanical injuries to the pharynx, esophagus, and stomach.

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Jul 7, 2016 | Posted by in CRITICAL CARE | Comments Off on General Toxicology and Toxidromes

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