A 32-year-old man is brought to the emergency department after a car accident; he was extricated after 4 hours. He did not lose consciousness and does not have headache or nausea. He is in severe pain. He sustained severe injuries to both arms and the trauma team determines that surgical intervention is needed. Urinary catheterization shows dark colored urine. His temperature is 38°C (100.4°F), pulse is 110/min, and blood pressure is 90/60 mm Hg. The patient is alert and oriented. Examination shows multiple injuries to the upper extremities, contusions on the trunk, and abdominal tenderness. Laboratory studies show: Hemoglobin 9.2 g/dL Leukocyte count 10,900/mm3 Platelet count 310,000/mm3 Serum Na+ 137 mEq/L K+ 6.8 mEq/L Cl- 97 mEq/L Glucose 168 mg/dL Creatinine 1.7 mg/dL Calcium 7.7 mg/dL Arterial blood gas analysis on room air shows a pH of 7.30 and a serum bicarbonate of 14 mEq/L. An ECG shows peaked T waves. A FAST scan of the abdomen is negative. Two large bore cannulas are inserted and intravenous fluids are administered. Which of the following is the most appropriate next step in management?

Packed red blood cell transfusion

A 54-year-old man is brought to the emergency department 1 hour after the sudden onset of shortness of breath, severe chest pain, and sweating. He has hypertension and type 2 diabetes mellitus. He has smoked one pack and a half of cigarettes daily for 20 years. An ECG shows ST-segment elevations in leads II, III, and avF. The next hospital with a cardiac catheterization unit is more than 2 hours away. Reperfusion pharmacotherapy is initiated. Which of the following is the primary mechanism of action of this medication?

Conversion of plasminogen to plasmin

Inhibition of glutamic acid residue carboxylation

Blocking of adenosine diphosphate receptors

Direct inhibition of thrombin activity

Prevention of thromboxane formation

A 72-year-old man comes to the emergency department because of severe, acute, right leg pain for 2 hours. The patient's symptoms started suddenly while he was doing household chores. He has no history of leg pain at rest or with exertion. Yesterday, he returned home after a 6-hour bus ride from his grandson's home. He has hypertension treated with ramipril. He appears uncomfortable. His temperature is 37.4°C (99.3°F), pulse is 105/min and irregular, and blood pressure is 146/92 mm Hg. The right lower extremity is cool and tender to touch. A photograph of the limb is shown. Femoral pulses are palpable bilaterally; popliteal and pedal pulses are decreased on the right side. Sensation to pinprick and light touch and muscle strength are decreased in the right lower extremity. Which of the following is most likely to confirm the underlying source of this patient's condition?

Doppler ultrasonography of the legs

Digital subtraction angiography

A patient in a phase 1 trial for a novel epoxide reductase inhibitor, being studied for stroke prophylaxis, develops pain and erythema on the right thigh two days after starting the trial. This rapidly progresses to a purpuric rash with necrotic bullae within 24 hours. Lab results show a PTT of 29 seconds, PT of 28 seconds, and INR of 2.15. What is the most likely pathogenesis of this condition?

Decreased antithrombin III activity

A 31-year-old man presents to the Emergency Department with severe left leg pain and paresthesias 4 hours after his leg got trapped by the closing door of a bus. Initially, he had a mild pain which gradually increased to unbearable levels. Past medical history is noncontributory. In the Emergency Department, his blood pressure is 130/80 mm Hg, heart rate is 87/min, respiratory rate is 14/min, and temperature is 36.8℃ (98.2℉). On physical exam, his left calf is firm and severely tender on palpation. The patient cannot actively dorsiflex his left foot, and passive dorsiflexion is limited. Posterior tibial and dorsalis pedis pulses are 2+ in the right leg and 1+ in the left leg. Axial load does not increase the pain. Which of the following is the best next step in the management of this patient?

Lower limb X-ray in two projections

A 65-year-old man comes to the emergency department because of sudden, worsening pain in his right calf and foot that started 30 minutes ago. He also has a tingling sensation and weakness in his right leg. He has had no similar episodes, recent trauma, or claudication. He has type 2 diabetes mellitus and was diagnosed with hypertension 20 years ago. His sister has systemic sclerosis. He works as an office administrator and sits at his desk most of the day. He has smoked one and a half packs of cigarettes daily for 30 years. Current medications include metformin and lisinopril. His pulse is 110/min, respirations are 16/min, and blood pressure is 140/90 mm Hg. His right leg is pale and cool to touch. Muscle strength in his right leg is mildly reduced. Pedal pulses are absent on the right. Which of the following is the most likely underlying cause of this patient's symptoms?

Atherosclerotic narrowing of the artery

Thromboembolectomy procedures for USMLE Step 2 CK: High-Yield Surgery Lessons

💉 Core Concept - Clot E-vacuation

Definition: Urgent removal of an occlusive thrombus or embolus from a vessel to restore perfusion, primarily for acute limb ischemia or massive PE.
Goal: Prevent irreversible tissue damage (e.g., limb loss, organ failure).
Main Approaches:
- Surgical (Open): Direct arteriotomy and clot extraction.
- Endovascular (Percutaneous): Catheter-directed mechanical thrombectomy (aspiration/fragmentation) or thrombolysis.

⭐ The Fogarty catheter is a classic tool for open embolectomy; its balloon tip is inflated past the clot and withdrawn, pulling the clot out.

Thrombectomy procedure with catheter

🩸 Pathophysiology - The Blockage Buildup

Foundation: Virchow's Triad initiates thrombus formation.
- Endothelial Injury (e.g., atherosclerosis)
- Abnormal Blood Flow/Stasis (e.g., AFib, aneurysm)
- Hypercoagulability (e.g., Factor V Leiden, malignancy)
Sources of Occlusion:
- Embolism (~80%): Abrupt onset. Most common source is cardiac (AFib, post-MI thrombus).
- Thrombosis (~20%): Slower onset. Forms in situ on a pre-existing, ruptured atherosclerotic plaque.

⭐ Irreversible nerve damage begins after ~6 hours of ischemia, progressing to muscle necrosis. The "time is tissue" principle mandates urgent revascularization.

🛑 Diagnosis - Spotting the Stop Sign

Clinical Presentation: Suspect acute limb ischemia (ALI) with the classic 6 P's. 📌 Mnemonic: The 6 P's
- Pain (early, severe)
- Pallor
- Pulselessness (confirm with Doppler)
- Paresthesia (late sign)
- Paralysis (late sign)
- Poikilothermia (cool to touch)
Diagnostic Imaging:
- Bedside Doppler: Confirms absent arterial flow.
- CT Angiography (CTA): Gold standard. Rapidly identifies the location and extent of the occlusion ("the stop sign").

⭐ Time is tissue! Irreversible nerve damage and muscle necrosis can begin within 4-6 hours of ischemia. Paresthesia and paralysis are ominous signs indicating threatened limb viability.

CT Angiography: Acute Limb Ischemia with Popliteal Occlusion

🛠️ Management - The Extraction Mission

Goal: Rapidly restore perfusion to prevent irreversible tissue damage. Choice depends on limb viability (Rutherford class), clot location, and patient stability.
Catheter-Directed Thrombolysis (CDT):
- Low-dose thrombolytic (e.g., tPA) infused via a multi-side-hole catheter directly into the clot.
- Best for stable patients with viable/marginally threatened limbs (Rutherford I/IIa) and recent thrombus (<14 days).
- ⚠️ Risk: Hemorrhage (especially intracranial).
Percutaneous Mechanical Thrombectomy (PMT):
- Uses aspiration or rheolytic devices to remove/fragment the clot.
- Often adjunctive to CDT to reduce lytic dose and procedure time.
Surgical Embolectomy:
- Gold standard for immediately threatened limbs (Rutherford IIb).
- Involves arteriotomy and passage of a Fogarty balloon catheter.

⭐ Post-procedure, watch for reperfusion injury & compartment syndrome. Prophylactic fasciotomy may be needed, especially if ischemia > 4-6 hours.

💥 Complications - The Aftermath

Reperfusion Injury: The most feared complication.
- Systemic "washout": Release of K+, lactate, myoglobin.
- Leads to: Hyperkalemia (↑$K^+$), metabolic acidosis, rhabdomyolysis → AKI.
- Local: Compartment syndrome from edema.
Hemorrhage: Often due to aggressive anticoagulation or vessel trauma.
Distal Embolization: Dislodged clot fragments occlude smaller, distal vessels.
Re-thrombosis: Early failure at the embolectomy site.

⭐ Sudden reperfusion can cause a massive release of intracellular potassium, leading to life-threatening cardiac arrhythmias. Always have calcium gluconate ready.

⚡ High-Yield Points - Biggest Takeaways

Primary Indication: Acute limb ischemia (ALI), classically presenting with the 6 P's (Pain, Pallor, Pulselessness, Paresthesia, Paralysis, Poikilothermia).

Procedure: A Fogarty balloon catheter is passed beyond the clot, inflated, and withdrawn to mechanically extract the thrombus.

Major Complication: Reperfusion injury, leading to compartment syndrome, rhabdomyolysis (↑CK), and life-threatening hyperkalemia.

Post-Procedure: Immediate systemic anticoagulation (IV heparin) is crucial to prevent re-thrombosis.

Adjunctive Surgery: Fasciotomy is often required to treat or prevent compartment syndrome after reperfusion.

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