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FM13.{1-10,21} | Toxicology: General Principles — PBL Case

CLINICAL SETTING

District General Hospital, rural India — 11:30 PM. A 52-year-old male farmer, Ramasamy, is brought in by his family. He was found collapsed in his paddy field two hours ago. His clothes smell of pesticide. He is deeply unconscious (GCS 6), with pinpoint pupils, excessive salivation and lacrimation, audible bronchospasm, bradycardia (HR 42 bpm), BP 90/60 mmHg, and urinary incontinence. His daughter says he has been repeatedly spraying his crop with an organophosphate compound (brand name Rogor) without protective equipment for the past three days due to a pest infestation. The family has brought the empty pesticide container.

Trigger 1: Scene at Arrival

The duty resident sees Ramasamy and immediately calls for help. The nurse notes: GCS 6/15, pupils 1 mm bilateral, copious oral secretions pooling, HR 42, BP 90/60. SpO₂ reads 91% on room air. The family shows the empty pesticide tin labelled 'Dimethoate 30% EC — Organophosphate Insecticide'. The resident is uncertain whether to perform gastric lavage or call for dialysis.

DISCUSSION POINTS

  • What toxidrome is being demonstrated, and which physiological receptor system is involved?
  • List the immediate priorities in managing this patient. Is gastric lavage appropriate at this stage?
  • What legislation governs the sale and use of this pesticide in India, and what are the employer's duties regarding personal protective equipment?
Click to reveal Trigger 2: Antidote Decision (discuss previous trigger first!)

Trigger 2: Antidote Decision

The senior resident orders 3 mg of atropine IV. After 10 minutes, secretions are somewhat reduced but bradycardia persists. A colleague suggests adding pralidoxime (PAM). The family reveals that the first dose of pesticide exposure was actually 36 hours ago, though today was his heaviest exposure. Blood sent for RBC cholinesterase activity is reported as 15% of normal.

DISCUSSION POINTS

  • What is the correct endpoint for atropine titration — and why is heart rate NOT the correct endpoint?
  • Should PAM be given given that the initial exposure was 36 hours ago? Explain the concept of 'ageing' of acetylcholinesterase.
  • What does 15% RBC cholinesterase activity signify in terms of poisoning severity?
Click to reveal Trigger 3: Decontamination Dilemma (discuss previous trigger first!)

Trigger 3: Decontamination Dilemma

Ramasamy is intubated and stabilised. The dermatologist on call notes significant dermal contamination on his forearms and neck. The team debates: (a) Should activated charcoal be given via the NGT? (b) Can haemodialysis be used to remove the poison faster? The consultant toxicologist arrives and asks for the viscera preservation protocol to be reviewed in case the patient does not survive.

DISCUSSION POINTS

  • Evaluate activated charcoal for this poisoning: is it indicated? Why or why not?
  • Would haemodialysis effectively remove organophosphate compounds? Justify using toxicokinetic principles.
  • If the patient were to die, how should visceral samples be collected for toxicological analysis? What preservatives must be used, and what must be AVOIDED?
Click to reveal Trigger 4: Medicolegal Aftermath (discuss previous trigger first!)

Trigger 4: Medicolegal Aftermath

Three days later, Ramasamy dies despite full intensive care. The family alleges the employer (a local landlord who provided the pesticide without PPE training) was responsible. The police arrive and ask the treating doctor for the case records and a medico-legal opinion. A post-mortem is ordered.

DISCUSSION POINTS

  • What are the treating doctor's medicolegal duties in this case — from admission through to the patient's death?
  • What evidence at autopsy would support a diagnosis of acute organophosphate poisoning?
  • Under what sections of Indian law could the employer be held liable? What role does the doctor's medico-legal report play in such a case?

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [FM13.1] Define 'poison' in the forensic context and distinguish from 'drug' in terms of dose-response relationship.
  2. [FM13.3] Describe the toxicokinetics of organophosphate compounds: absorption, distribution, mechanism of toxicity at the molecular level.
  3. [FM13.6] Outline the stepwise general management of acute poisoning with specific reference to OP compounds.
  4. [FM13.5] What are the medicolegal duties of a treating doctor in a case of suspected occupational/homicidal poisoning?
  5. [FM13.9] Describe correct autopsy technique for sample collection and preservation when toxicological analysis is required.
  6. [FM13.21] What are the occupational exposure standards for pesticides in India, and what biological monitoring is recommended for agricultural workers?