Vascular Injury

Introduction

Vascular injury represents a critical component of trauma surgery and emergency medicine. For the MCCQE1, candidates must demonstrate the ability to rapidly assess, diagnose, and manage vascular trauma to prevent loss of life and limb. This topic integrates the CanMEDS roles of Medical Expert (clinical decision making) and Collaborator (working with trauma teams, vascular surgeons, and interventional radiologists).

Epidemiology and Etiology in Canada

In the Canadian context, the mechanism of vascular injury varies significantly between urban trauma centres and rural settings.

• Penetrating Trauma: More common in urban centres (stab wounds, gunshot wounds).
• Blunt Trauma: More common in rural and highway settings (motor vehicle collisions, farming accidents).

Mechanisms of Injury

Clinical Assessment: Hard vs. Soft Signs

This is the highest yield concept for the MCCQE1 regarding vascular injury. The presence of “Hard Signs” mandates immediate surgical intervention, while “Soft Signs” dictate further investigation.

Diagnostic Approach

For MCCQE1 preparation, follow this stepwise algorithm for a hemodynamically stable patient with potential vascular injury.

Specific High-Yield Injuries

1. Knee Dislocation and Popliteal Artery Injury

• Anatomy: The popliteal artery is tethered at the adductor hiatus and the soleal arch, making it susceptible to traction injury during knee dislocation.
• MCCQE1 Pearl: Any patient with a knee dislocation (anterior or posterior) must have vascular status assessed.
• Management: If pulses are absent → Immediate reduction. If pulses remain absent → Surgery. If pulses present → ABI/CTA (intimal tears are common).

2. Thoracic Aortic Injury (Blunt Aortic Injury - BAI)

• Mechanism: Rapid deceleration (e.g., high-speed MVC, fall from height).
• Site: Most commonly at the aortic isthmus (just distal to the left subclavian artery).
• Chest X-Ray Findings: Widened mediastinum (>8cm), loss of aortic knob, deviation of trachea/NG tube to the right, apical cap.
• Diagnosis: CTA Chest is the gold standard.

3. Compartment Syndrome

A limb-threatening complication of vascular injury and reperfusion.

• Pathophysiology: Increased pressure within a closed fascial space reduces capillary perfusion.
• Diagnosis: Clinical (Pain out of proportion to injury, pain on passive stretch). Compartment pressure measurement (Stryker needle) if obtunded: Delta pressure (ΔP) < 30 mmHg is diagnostic.
  • Formula: $\Delta P = \text{Diastolic BP} - \text{Compartment Pressure}$
• Treatment: Emergent 4-compartment fasciotomy.

Management Strategies

Damage Control Surgery

In unstable patients (acidosis, hypothermia, coagulopathy), complex repair is contraindicated.

1. Temporary Vascular Shunt: Restores flow rapidly.
2. Ligation: For non-essential veins or minor arteries where collateral flow exists.
3. Fasciotomy: Prophylactic if ischemia time is prolonged.

Canadian Guidelines & Context

1. Transfer Protocols: In Canada, rural physicians must stabilize and transfer patients with vascular injuries to tertiary trauma centres. Understanding the capabilities of your centre and initiating early transport (Ornge, STARS, etc.) is a key Collaborator skill.
2. Blood Transfusion: Canadian Blood Services guidelines advocate for massive transfusion protocols (MTP) with a 1:1:1 ratio (RBCs:Plasma:Platelets) in major trauma.
3. Choosing Wisely Canada: Do not order imaging for soft signs if the ABI is normal (≥ 0.9), unless the mechanism is high-risk (e.g., knee dislocation) or clinical suspicion is extremely high.

Key Points to Remember for MCCQE1

• Hard Signs = Operating Room. Soft Signs = ABI/Imaging.
• Knee Dislocation = High index of suspicion for Popliteal Artery injury.
• Posterior Knee Dislocation is the most dangerous for the popliteal artery.
• ABI < 0.9 warrants a CTA.
• Pain out of proportion is the earliest sign of compartment syndrome. Pulselessness is a late sign.
• Great Saphenous Vein from the contralateral leg is the conduit of choice for arterial bypass/grafting.
• Prophylactic Fasciotomy should be considered if ischemia time > 6 hours or in combined arterial/venous injuries.

Sample Question

Case Presentation

A 27-year-old male is brought to the Emergency Department following a high-speed motorcycle collision. He has a deformed right knee which was reduced by paramedics at the scene. On arrival, his GCS is 15. Vital signs are HR 110 bpm, BP 125/75 mmHg. On examination of the right lower extremity, there is significant swelling around the knee. The foot is cool and pale compared to the left. The dorsalis pedis and posterior tibial pulses are not palpable, whereas they are 2+ on the left. Sensation is decreased on the dorsum of the right foot.

Which one of the following is the most appropriate next step in management?

Options

• A. Measure compartment pressures in the right calf
• B. Perform an immediate CT Angiography (CTA) of the right leg
• C. Emergent surgical exploration of the right popliteal artery
• D. Calculate the Ankle-Brachial Index (ABI)
• E. Apply traction and immobilize the leg

Explanation

The correct answer is:

• C. Emergent surgical exploration of the right popliteal artery

Detailed Analysis: This patient presents with a knee dislocation (suggested by mechanism and reduction) and Hard Signs of vascular injury. The hard signs present are:

1. Pallor/Coolness (Ischemia)
2. Pulselessness (Absent distal pulses)
3. Paresthesia (Decreased sensation)

According to ATLS and vascular trauma guidelines relevant to the MCCQE1:

• Hard Signs mandate immediate surgical exploration to restore blood flow. Delaying for imaging (CTA) consumes valuable ischemia time and threatens limb viability.
• Option A: Compartment syndrome is a risk, but revascularization is the priority. Fasciotomy is often performed during or after revascularization.
• Option B: CTA is indicated for Soft Signs or when the diagnosis is unclear. Here, the clinical diagnosis of arterial compromise is obvious.
• Option D: ABI is a screening tool for equivocal cases (Soft Signs). It is unnecessary and delays care when pulses are blatantly absent.
• Option E: The knee has already been reduced. While immobilization is part of care, it does not address the critical ischemia.

References

1. Medical Council of Canada. Objectives for the Qualifying Examination. Available at: mcc.ca 
2. American College of Surgeons. Advanced Trauma Life Support (ATLS) Student Course Manual. 10th Edition. Chicago, IL: American College of Surgeons; 2018. (Standard of care in Canada).
3. Canadian Society for Vascular Surgery. Clinical Practice Guidelines.
4. Feliciano DV, et al. Management of vascular injuries. In: Trauma. 8th ed. New York, NY: McGraw-Hill Education; 2017.
5. Choosing Wisely Canada. Trauma and Emergency Medicine Recommendations. Available at: choosingwiselycanada.org