Organophosphate Toxicity

Question 1

Which muscle relaxant should be used to intubate a patient with organophosphate toxicity and why

Answer 1

Organophosphate toxicity is inactivation of acetylcholinesterase and abundant acetylcholine with resulting effects on ANS, PNS and CNS. In the PNS - acetylcholinesterase metabolizes succinylcholine. Hence use of sux for RSI will result in prolonged and unpredictable neuromuscular blockade.
Rocuronium can be used but as it is a competitive (with Ach) antagonist, larger doses are required for same clinical effect.

Question 2

Why can mydriasis, tachycardia, hypertension and bronchospasm counterintuitively occur in a cholinergic toxidrome?

Answer 2

Some SNS ganglia also contain nicotinic receptors –> SNS effects

Question 3

Why does sweating sometimes occur in cholinergic toxidrome

Answer 3

Sweating occurs because sweat glands are regulated through SNS activation of postganglionic MUSCARINIC receptors

Question 4

How can the diagnosis of organophosphate toxicity by made

Answer 4

• Clinical toxidrome
• Atropine: 1mg –> absence of anticholinergic effects = highly supportive of diagnosis
• measure RBC Achesterase (poor availability)

Question 5

What is the mechanism of action of atropine in organophosphate poisoning

Answer 5

Atropine competes with acetylcholine at muscarinic receptors, preventing cholinergic activation.

Question 6

What is the dose and method of adminstration of atropine to a patient with organophosphate poisoning?

Answer 6

Initial dose: 2 - 5 mg (0.05mg/kg kids)
Double dose every 5 minutes until pulmonary muscarinic signs and symptoms are alleviated (clear resp. secretions and resolve bronchoconstriction)

Followed by 10 - 20% of the total initial bolus as an infusion per hour

Adjust infusion until adequate response and then taper until recovery

Question 7

Tachycardia and mydriasis are not appropriate markers for therapeutic improvement, why

Answer 7

They may indicate ongoing:
1. Hypoxia
2. Hypercapnoea
3. Hypovolaemia
4. SNS activation

Question 8

What are the goals of atropine infusion in patients with organophosphate poisoning

Answer 8

1. Clear lung auscultation
2. HR > 80 bpm
3. SBP > 80 mmHg
4. Dry axillae
5. Miosis resolved

without causing atropine toxicity
1. Confusion
2. Pyrexia
3. Absent bowel sounds
4. Urinary retention

Question 9

What should be done if the patient becomes atropine toxic

Answer 9

Hold the infusion until the patient is no longer atropine toxic and then restart the infusion at 70 - 80 % of the rate

Question 10

How should organophsophate related seizures be treated

Answer 10

1. Supportive Rx
2. Benzodiazepines
   (Phenytoin not indicated)

Question 11

How and when is activated charcoal administered in organophosphate poisoning

Answer 11

If patient presents within 1 hour of ingestion
dose 1 g/kg (max 50g)

Question 12

Explore the options for decontamination in OP poisoning

Answer 12

1. < 1 hr - activated charcoal
2. , 1 hr - may gastric lavage after ETT/Atropine
3. Never forced emesis
4. Urinary alkalinization - no evidence