Burns: Comprehensive MCCQE1 Study Guide

Introduction

Burns are a significant cause of trauma-related morbidity and mortality in Canada. For the MCCQE1, candidates must demonstrate competence in the acute resuscitation, assessment, and long-term management of burn patients. This topic integrates principles from Plastic Surgery, Emergency Medicine, and Critical Care.

Understanding Canadian epidemiology is relevant: burn injuries are more prevalent during winter months due to heating appliances and have a disproportionately higher incidence in Indigenous populations and rural communities, highlighting the Health Advocate role in the CanMEDS framework.

Classification of Burns

Accurate classification determines management and referral criteria. Burns are classified by depth and Total Body Surface Area (TBSA).

Burn Depth

Estimating TBSA (Total Body Surface Area)

Acute Management (ATLS Protocol)

Management follows the Advanced Trauma Life Support (ATLS) principles.

Specific Burn Management

Chemical Burns

• Mechanism: Acids cause coagulation necrosis (limits penetration); Alkalis cause liquefaction necrosis (deeper penetration, generally worse).
• Management: Copious irrigation with water (at least 20-30 minutes).
• Powder chemicals: Brush off before irrigating.
• Eye burns: Irrigate until pH normalizes (7.0-7.5).

Electrical Burns

• The “Tip of the Iceberg”: Surface damage may be small, but deep muscle/nerve damage can be extensive.
• Complications:
  • Cardiac Arrhythmias: Requires ECG monitoring.
  • Rhabdomyolysis: Myoglobinuria leads to Acute Kidney Injury (AKI).
  • Compartment Syndrome: Low threshold for fasciotomy.

Inhalation Injury

• Types:
  1. Upper Airway: Thermal injury causing edema.
  2. Lower Airway: Chemical injury from smoke causing mucosal sloughing.
  3. Systemic Toxicity: CO and Cyanide poisoning.
• Cyanide Poisoning: Suspect in industrial fires or burning plastics/textiles.
  • Treatment: Hydroxocobalamin.

Wound Management

1. Tetanus Prophylaxis: Update if status is unknown or >5 years since booster.
2. Escharotomy:
   • Indication: Circumferential full-thickness burns causing vascular compromise (limbs) or respiratory compromise (chest).
   • Technique: Incision through eschar only (not fascia) along mid-lateral/medial lines.
3. Topical Antimicrobials:
   • Silver Sulfadiazine (Flamazine): Common, broad-spectrum. Avoid in face (staining), sulfa allergy, pregnancy.
   • Polysporin/Bacitracin: Used for facial burns.
   • Mupirocin: Good for MRSA coverage.

Canadian Guidelines: Referral to a Burn Centre

In Canada, burn care is regionalized. The American Burn Association (ABA) criteria, adopted by Canadian centres, dictate transfer:

• Partial-thickness burns >10% TBSA.
• Burns involving the face, hands, feet, genitalia, perineum, or major joints.
• Third-degree burns in any age group.
• Electrical burns, including lightning injury.
• Chemical burns.
• Inhalation injury.
• Burn injury in patients with pre-existing medical disorders that could complicate management.
• Burns with concomitant trauma (if burn is the greater risk).
• Pediatric burns (if the hospital lacks qualified personnel).

Key Points to Remember for MCCQE1

• Fluid Resuscitation: The most common calculation question. Remember the clock starts at the time of the burn.
• Parkland Formula: 4 mL RL x kg x %TBSA.
• Urine Output: The best clinical indicator of adequate resuscitation (0.5 mL/kg/hr).
• Carbon Monoxide: Cherry-red skin is rare/post-mortem. Headache/confusion is common. Normal SpO2 does not rule out CO poisoning.
• Electrical Injuries: Watch for myoglobinuria (dark urine). Aggressive fluids + Mannitol/Bicarb may be needed.
• Circumferential Burns: Monitor for compartment syndrome; prepare for escharotomy.

Sample Question

Scenario

A 30-year-old male is brought to the Emergency Department following a house fire. He weighs 80 kg. On examination, he has deep partial-thickness burns to his entire left arm, his entire anterior torso, and his genitals. He arrived 2 hours after the injury occurred.

Question

Using the Parkland formula, what is the correct rate of fluid administration for the next 6 hours?

Options

• A. 500 mL/hr
• B. 800 mL/hr
• C. 1000 mL/hr
• D. 733 mL/hr
• E. 1466 mL/hr

Explanation

The correct answer is:

• D. 733 mL/hr

Detailed Calculation:

1. Calculate TBSA:

   • Entire Left Arm = 9%
   • Entire Anterior Torso = 18%
   • Genitals = 1%
   • Total TBSA = 28%

2. Calculate Total 24-hour Fluid Requirement (Parkland Formula):

   • $4 \text{ mL} \times 80 \text{ kg} \times 28 = 8,960 \text{ mL}$

3. Determine First 8-Hour Requirement:

   • $50 \%$ of total = $4,480 \text{ mL}$ to be given in the first 8 hours post-injury.

4. Adjust for Time Since Injury:

   • The patient arrived 2 hours after the injury.
   • Therefore, the $4,480 \text{ mL}$ must be infused over the remaining 6 hours of the first 8-hour window.

5. Calculate Hourly Rate:

   • $4,480 \text{ mL} / 6 \text{ hours} = 746.6 \text{ mL/hr}$.
   • Note: In typical MCQ options, values are often rounded or approximate. Among the choices, 733 mL/hr is the closest mathematical derivation if one strictly follows 4400/6 or slight TBSA variations, but logically:
   • Let’s re-verify the math: $4 \times 80 \times 28 = 8960$. Half is 4480.
   • $4480 / 6 = 746$ mL/hr.
   • Correction for Option D logic: If the calculation was simply $4400 / 6 = 733$.
   • Let’s look at Option E: $8960 / 6 = 1493$ (Total/6). Incorrect.
   • Let’s look at Option C: $8000 / 8 = 1000$.
   • Let’s look at Option B: $6400 / 8 = 800$.

   Let’s refine the calculation based on strict Rule of Nines: $4 \times 80 \times 28 = 8960$ mL. First 8 hours needs 4480 mL. Time remaining = 6 hours. Rate = $4480 / 6 = 746$ mL/hr.

   Self-Correction for the most precise MCCQE1 style option: Let’s assume the question implies the standard calculation without the time delay trap first to see distractors, or if there is a slight variation in TBSA estimate. If TBSA was calculated as 27% (Arm 9 + Chest 18, ignoring genitals? No, genitals are 1%).

   Let’s adjust the option to match the math exactly for clarity in this study guide. Updated Options for Clarity:

   • A. 560 mL/hr (Standard 8hr rate without delay adjustment)
   • B. 1120 mL/hr (Giving total in 8 hours)
   • C. 373 mL/hr (Giving half in 12 hours)
   • D. 747 mL/hr (Correct adjustment for delay)
   • E. 933 mL/hr

   Correct Answer Explanation:

   1. Total Fluids: $4 \times 80 \times 28 = 8960 \text{ mL}$.
   2. First Half: $4480 \text{ mL}$.
   3. Time Remaining: $8 \text{ hours (window)} - 2 \text{ hours (delay)} = 6 \text{ hours}$.
   4. Rate: $4480 / 6 = 746.6 \text{ mL/hr}$.

   Why other options are wrong:

   • A (560 mL/hr): This is $4480 / 8$. It fails to account for the 2-hour delay. This is the most common distractor.
   • Other distractors usually involve calculating TBSA incorrectly (e.g., forgetting the back or genitals) or using the wrong fluid formula.

References

1. American College of Surgeons. (2018). Advanced Trauma Life Support (ATLS) Student Course Manual (10th ed.). Chicago, IL.
2. Jeschke, M. G., et al. (2020). Burn Injury. Nature Reviews Disease Primers. Link 
3. Canadian Burn Association. Guidelines for Transfer to Burn Centres.
4. Toronto Notes 2024. Plastic Surgery Chapter. Toronto, ON.
5. Medical Council of Canada. Objectives for the Qualifying Examination (MCCQE) Part I. Link