Tales from a Haunted Farmhouse: Organophosphate Poisoning

halloweencat

It’s Halloween! You just finished a rough shift (trying to figure out fake blood and real blood isn’t always as easy as it seems). You’re headed to a Halloween party in your go-to doctor scrub costume with a warm, pumpkin spice latte in hand. As you get closer to your destination, you see a sign that reads “Haunted Farmhouse – Free Tours!” You can’t resist a good haunted house! You walk in, and immediately a foggy mist surrounds you. Cool! Wait… the fog smells like garlic, and soon you start to feel a little lightheaded… You realize it wasn’t just fog. It was a pesticide. Guess you got tricked – now time to get treated.

Describe the pathophysiology of organophosphate poisoning.

Organophosphates bind to and inhibit acetylcholinesterase (an enzyme that breaks down acetylcholine) leading to accumulation of acetylcholine at nerve synapses and neuromuscular junctions, causing overstimulation. Eventually, this also leads to paralysis of stimulation. Muscarinic receptors, which are found in the parasympathetic chain ganglion, are predominately affected. The parasympathetic system is responsible for the body’s “rest and digest” functions. acetylcholine_receptors_ans

In short, organophosphates -> inhibition of acetylcholinesterase -> excess acetylcholine -> parasympathetic stimulation -> SLUDGE, DUMBELS, Killer Bee (more on this later)

Describe the concept of aging with organophosphate poisoning

The time that it takes for organophosphate compounds to bind and permanently inactivate acetylcholinesterase is called aging. Once aging happens, new enzymes must be synthesized before symptoms resolve, and this may take weeks. Antidotes will be ineffective once aging as occurred.

What is SLUDGE, DUMBELS, Killer Bee?

SLUDGE, DUMBELL, and Killer Bee are mnemonics to help you remember what the effects of parasympathetic overstimulation. Just think of a lot of bodily fluids coming out – fitting with our Halloween theme.

Salivation
Lacrimation
Urinary incontinence
Defecation
GI pain
Emesis

Defecation
Urination
Muscle weakness, Miosis
Bradycardia, Bronchorrhea, Bronchospasm (Also the Killer Bees). The Killer Bees are dangerous effects of organophosphate poisoning.
Emesis
Lacrimation
Salvation

What’s with the garlic odor?

Garlic odor can be a give away on exam questions about organophosphate poisoning.

Let’s talk antidotes. What can we give to treat organophosphate poisoning?

Atropine: A competitive acetylcholine antagonist at muscarinic receptors. Starting dose is 1mg IV and should be titrated to effect (reduction of bronchosecretions). It does not reverse muscle weakness (nicotinic receptors are found in neuromuscular junctions).

Initial dose for adults: 1mg IV
Initial dose for pediatrics: 0.01-0.04mg/kg (never less than 0.1mg) IV
You can give up to 6mg IM if you cannot obtain IV access
Dose may be repeated every 5 minutes until titrated effect

Pralidoxime: A compound that displaces organophosphate compounds from acetylcholinesterase enzymes and allows the enzyme to regain function. Pralidoxime relieves parasympathetic symptoms AND muscle weakness (if given before aging).

In summary…

Organophosphates inhibit anticholinesterases leading to overstimulation of parasympathetic function (think wet). Reverse it with atropine and pralidoxime.

References:
Robey, Walter C., III, and William J. Meggs. “Chapter 195. Pesticides.” Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7e. Eds. Judith E. Tintinalli, et al. New York, NY: McGraw-Hill, 2011

Remember, what we do in practice may not always be the right answer on the exam. Frustrating, I know, but don’t cry, poop, pee, or puke about it.

Special thanks to Dr. Willis and Dr. deSouza