Setting: ED
CC: “I got splashed with insecticide; now I can’t breathe.”
VS: BP: 92/72 mm Hg; P: 56 beats/minute; T: 98°F; R: 36 breaths/minute
HPI: A 57-year-old farmer comes to the ED after a bag of insecticide was accidentally splashed on his face while working on his farm. He had diarrhea, vomiting, and difficulty breathing. He is spitting continuously since the exposure occurred. He asks for a urinal twice while giving the history. There is no burning with urination. He denies fever or cough.
PMHx/Medications: none
What is the most common cause of death from insecticide poisoning?
a. Aspiration pneumonia
b. Diarrhea
c. Heart block
d. Respiratory failure
e. Infection
Answer d. Respiratory failure
Insecticides contain organophosphates, which markedly increase ACh levels. Massive increases in ACh levels cause death from respiratory distress, bronchospasm, and diaphragmatic paralysis. Although there is diarrhea, heart block, urinary frequency, and excess salivation, these do not cause death.
ACh increases salivary volume.
Normally, 1 to 2 L/day of saliva are made.
What is the most important thing to do first?
a. Remove the clothes.
b. Wash the patient.
c. Give atropine.
d. Intubate and begin mechanical ventilation.
e. Give pralidoxime.
Answer c. Give atropine.
All of these efforts, except intubating the patient, should be done. Decontamination with removing the clothes and washing the patient is important, but not as important as stopping the effects of the extra ACh already inside the body. No matter how much you wash the skin, it will not stop the effects of the organophosphate already inside it.
The emergency medicine section of CCS has the largest number of cases where treatment before the physical examination is done. Correct timing or the right order of testing and treatment is the essence of CCS.
Saliva
• Muscarinic receptors stimulate secretion.
• Secretions are serous.
• ACh increases the bicarbonate content of saliva.
Orders:
Atropine IV
Oxygen
Decontamination of patient’s skin (Wash the patient’s skin.)
PE:
General: uncomfortable man on stretcher in an isolation room
Chest: bilateral wheezing
HEENT: constricted pupils
Cardiovascular: slow heart rate, no murmurs
Abdomen: hyperactive bowel sounds
ACh constricts the pupils.
What is the mechanism of the patient’s current respiratory distress?
a. ACh constricts bronchial smooth muscle.
b. The central (medullary) drive is decreased.
c. The pulmonary vasculature is constricted.
d. The pulmonary vasculature is dilated.
e. The peripheral chemoreceptors are blocked.
Answer a. ACh constricts bronchial smooth muscle.
ACh is increased from insecticide exposure by blocking its metabolism. ACh in the lung has a direct effect on:
• Constricting bronchial smooth muscle
• Increasing bronchial gland secretions
ACh has no effect at all on the medullary respiratory centers or smooth muscle in the vasculature. Although the autonomic nervous system is usually paired in opposite directions, with ACh increasing GI tract motility and norepinephrine (NE) decreasing it, or ACh decreasing heart rate and NE increasing it, this is not true of vascular smooth muscle. NE will constrict smooth muscle by alpha-1 stimulation. ACh has no effect on vascular smooth muscle to either constrict it or dilate it.
Central Chemoreceptors
• Increasing carbon dioxide
• Acid
ACh slows heart rate
• Decreased sinoatrial (SA) and atrioventricular (AV) node automaticity
ACh
• Flattens the slope of phase 4 depolarization
• Increases the time to achieve threshold for depolarization
• Slows conductance through Funny sodium channels
Ordering a physical examination moves the clock forward. Atropine is considered to be done instantly on CCS, so if there is an effect of atropine, you will see it right away.
Interval History: “Breathing improved somewhat. Feeling better.”
Orders:
Repeat IV atropine
Pralidoxime
CHEM-7, CBC
ECG
Chest x-ray
ACh
• Constricts intestinal smooth muscle
• Leads to diarrhea
• Constricts stomach smooth muscle
• Leads to vomiting
Which is the mechanism of excess ACh with insecticides?
a. Increased release from neuron
b. Prevention of splitting into acetic acid and choline
c. Blockade of neuromuscular junction
d. Increased calcium flow into presynaptic neuron
Answer b. Prevention of splitting into acetic acid and choline
Acetylcholinesterase ends the effect of ACh at the neural junction. This happens by splitting ACh into acetic acid and choline. This effect is most apparent at muscarinic receptors, which are:
• Salivary and lacrimal glands
• GI tract smooth muscle: distal esophagus, stomach, and, intestine
• Urinary bladder smooth muscle (detrusor muscle)
Pralidoxime reactivates acetylcholinesterase.
Move the clock forward at increments of 15 minutes at first. You should expect to re-dose atropine numerous times. The half-life of atropine is short and the half-life of organophosphate insecticides is long. You should see all the effects resolve within minutes if you have given enough.
You do not have to do anything to get reports of tests ordered on CCS except to move past the time that it says “report available.” The report will pop up automatically as you pass the time. You can cancel a test at any time before it becomes available by double clicking on it.
Reports:
CHEM-7, CBC: normal
ECG: sinus bradycardia (timed before repeat dose of atropine)
Chest x-ray: normal
After repeated doses of atropine, there is no effect on muscular strength. What accounts for this?
a. Atropine does not penetrate muscles.
b. The neuromuscular junction is nicotinic.
c. Muscles are stimulated by calcium in the junction, not atropine.
d. The mechanism is unknown.
Answer b. The neuromuscular junction is nicotinic.
Atropine only effects muscarinic receptors such as are found in saliva, GI, bowel, and bladder tissue.
Move the clock forward at 30- to 60-minute intervals for the first 12 hours because of the short half-life of atropine. The management of nerve gas such as sarin gas is identical to the management of insecticides.
Nerve gas attack presents the same way:
• Salivation
• Lacrimation
• Urination
• Defecation
• Respiratory distress