Poisoning

Introduction to Poisoning in the Canadian Context

Poisoning is a significant public health concern in Canada, affecting individuals across all age groups. As future Canadian physicians preparing for the MCCQE1, understanding the epidemiology, diagnosis, and management of poisoning cases is crucial. This guide will provide you with the essential knowledge required for the MCCQE1 exam, focusing on Canadian guidelines and practices.

Epidemiology of Poisoning in Canada

Understanding the Canadian epidemiology of poisoning is crucial for MCCQE1 success:

• In Canada, the most common substances involved in poisoning cases include:

  1. Prescription medications (especially opioids)
  2. Over-the-counter medications
  3. Household cleaning products
  4. Alcohol
  5. Recreational drugs

• Age-specific considerations:

  • Children: Accidental ingestions are more common
  • Adolescents and young adults: Intentional overdoses and recreational drug use
  • Elderly: Medication errors and interactions

Diagnosis and Assessment

When preparing for the MCCQE1, focus on the following diagnostic approach:

Common Toxidromes

Understanding toxidromes is crucial for MCCQE1 success. Here's a summary table:

Management of Poisoning

For MCCQE1 preparation, focus on the following management principles:

1. Supportive care: Always the first priority
2. Decontamination: Consider gastric lavage, activated charcoal, or whole bowel irrigation based on specific indications
3. Enhanced elimination: Techniques like hemodialysis or multi-dose activated charcoal for certain toxins
4. Antidotes: Familiarize yourself with common antidotes used in Canadian practice

Key Antidotes for MCCQE1

Canadian Guidelines for Poisoning Management

The Canadian Association of Poison Control Centres (CAPCC) provides guidelines for poison management. Key points to remember for the MCCQE1:

1. Always consult with a local poison control center for up-to-date management advice
2. Follow provincial/territorial guidelines for reporting cases of poisoning
3. Familiarize yourself with the Canadian Triage and Acuity Scale (CTAS) for prioritizing poisoning cases in emergency departments

Key Points to Remember for MCCQE1

• Recognize common toxidromes and their associated poisons
• Understand the initial approach to a poisoned patient (ABCs, history, physical exam, investigations)
• Know the indications and contraindications for gastric decontamination methods
• Familiarize yourself with common antidotes used in Canadian practice
• Understand the role of supportive care in poisoning management
• Be aware of Canadian-specific guidelines and resources for poison management
• Know when to consult with poison control centers and how to access them in different provinces/territories

Sample Question

A 32-year-old woman is brought to the emergency department by her partner after ingesting an unknown quantity of her mother's blood pressure medication approximately 2 hours ago. She is drowsy but arousable. Her vital signs are: BP 80/50 mmHg, HR 45 bpm, RR 16/min, T 36.5°C. Physical examination reveals dry mucous membranes and cool extremities. Which one of the following is the most appropriate next step in management?

• A. Administer activated charcoal
• B. Perform gastric lavage
• C. Start intravenous glucagon infusion
• D. Administer intravenous calcium gluconate
• E. Initiate hemodialysis

Explanation

The correct answer is:

• C. Start intravenous glucagon infusion

This patient is presenting with signs and symptoms consistent with beta-blocker toxicity, likely due to ingestion of her mother's blood pressure medication. The key features suggesting beta-blocker overdose are:

1. Hypotension (BP 80/50 mmHg)
2. Bradycardia (HR 45 bpm)
3. CNS depression (drowsiness)

In beta-blocker toxicity, glucagon is the first-line antidote. Glucagon works by activating adenylyl cyclase through a G-protein coupled receptor that is separate from the beta-receptor, thereby bypassing the blocked beta receptors and increasing cAMP levels in cardiac cells. This leads to positive inotropic and chronotropic effects, helping to counteract the bradycardia and hypotension.

Let's review the other options:

A. Activated charcoal: While potentially useful in some poisonings, it's less effective after 1-2 hours post-ingestion and doesn't address the immediate cardiovascular effects.

B. Gastric lavage: Not recommended in this case due to the time since ingestion and the patient's drowsy state, which increases aspiration risk.

D. Calcium gluconate: While calcium can be useful in calcium channel blocker toxicity, it's not the first-line treatment for beta-blocker overdose.

E. Hemodialysis: Not typically indicated for beta-blocker toxicity and doesn't address the immediate cardiovascular effects.

References

1. Canadian Association of Poison Control Centres. (2021). Guidelines for the Management of Poisoning in Canada. https://www.capcc.ca/en/resources (opens in a new tab)

2. Health Canada. (2022). Canadian Alcohol Low-Risk Drinking Guidelines. https://www.canada.ca/en/health-canada/services/substance-use/alcohol/low-risk-alcohol-drinking-guidelines.html (opens in a new tab)

3. Hoffman, R. S., Howland, M. A., Lewin, N. A., Nelson, L. S., & Goldfrank, L. R. (2019). Goldfrank's Toxicologic Emergencies, 11th Edition. McGraw-Hill Education.

4. Canadian Institute for Health Information. (2022). Injury and Trauma Emergency Department and Hospitalization Statistics. https://www.cihi.ca/en/injury-and-trauma (opens in a new tab)

5. Grunau, B. E., Wiens, M. O., & Brubacher, J. R. (2019). Dextrose in the prehospital treatment of hypoglycemia: A systematic review. Canadian Journal of Emergency Medicine, 21(2), 214-221.