A 78-year-old woman presents to the orthopedic department for an elective total left knee arthroplasty. She has had essential hypertension for 25 years and type 2 diabetes mellitus for 35 years. She has smoked 20–30 cigarettes per day for the past 40 years. The operation was uncomplicated. On day 3 post-surgery, she complains of left leg pain and swelling. On examination, her left leg appears red and edematous, and there are dilated superficial veins on the left foot. Using Wells’ criteria, the patient is diagnosed with a provoked deep venous thrombosis. Which of the following is the best initial therapy for this patient?

Inferior vena cava (IVC) filter

A 62-year-old man comes to the physician because of a 5-day history of swelling in his left arm. Two months ago, he was diagnosed with a deep venous thrombosis in the left calf. He has had a 7-kg (15-lb) weight loss in the last 3 months. He has smoked 1 pack of cigarettes daily for the past 25 years. His only medication is warfarin. Physical examination shows warm edema of the left forearm with overlying erythema and a tender, palpable cord-like structure along the medial arm. His lungs are clear to auscultation bilaterally. Duplex sonography shows thrombosis of the left basilic and external jugular veins. Which of the following is the most appropriate next step to confirm the underlying diagnosis?

Transesophageal echocardiography

Serum antiphospholipid antibody level

A 68-year-old man undergoes successful mechanical prosthetic aortic valve replacement for severe aortic valve stenosis. After the procedure, he is started on an oral medication and instructed that he should take for the rest of his life and that he should avoid consuming large amounts of dark-green, leafy vegetables. Which of the following laboratory parameters should be regularly monitored to guide dosing of this drug?

Activated partial thromboplastin time

A 56-year-old man comes to the emergency department because of progressive swelling and pain in his left calf for 1 day. He does not have shortness of breath or chest pain. He has hypertension and chronic kidney disease. Current medications include enalapril, aspirin, simvastatin, and vitamin D. His temperature is 100.4°F (38°C), pulse is 84/min, and blood pressure is 135/92 mm Hg. Physical examination shows tenderness and swelling of the left lower extremity. A venous Doppler ultrasonography shows a thrombus in the left popliteal vein. Treatment with unfractionated heparin is begun. Two days later, physical examination shows improvement of symptoms. Laboratory studies at admission and 2 days after admission show: Admission Two days after admission Hemoglobin 11.2 g/dL 11.1 g/dL Leukocyte count 5,500/mm3 6,100/mm3 Platelet count 230,000/mm3 170,000/mm3 Serum Prothrombin time 12 seconds 13 seconds Partial thromboplastin time 30 seconds 55 seconds Estimated glomerular filtration rate 29 mL/min/1.73 m2 28 mL/min/1.73 m2 Which of the following is the most appropriate next step in management?

Discontinue heparin and initiate argatroban

Continue unfractionated heparin

A 28-year-old woman presents to the emergency department with fever, cough, and difficulty in breathing for the last 6 hours. She also mentions that she noticed some blood in her sputum an hour ago. She denies nasal congestion or discharge, sneezing, wheezing, chest pain, or palpitation. Her past history does not suggest any chronic medical condition, including respiratory disease, cardiovascular disease, or cancer. There is no history of pulmonary embolism or deep vein thrombosis in the past. Her temperature is 38.3°C (101.0°F), the pulse is 108/min, the blood pressure is 116/80 mm Hg, and the respirations are 28/min. Auscultation of her lungs reveals the presence of localized crackles over the right inframammary region. Edema is present over her left leg and tenderness is present over her left calf region. When her left foot is dorsiflexed, she complains of calf pain. The emergency department protocol mandates the use of a modified Wells scoring system in all patients presenting with the first episode of breathlessness when there is no history of a cardiorespiratory disorder in the past. According to the modified Wells scoring system, which of the following risk factors, if present, would contribute the most points toward a high clinical probability of pulmonary embolism?

History of surgery within the last 30 days

Use of oral contraceptives within last 90 days

Intravenous drug use within last 14 days

History of travel of 2 hours in 30 days

History of smoking for more than 1 year

A 52-year-old woman presents to the emergency room complaining of chest pain. She reports a 4-hour history of dull substernal pain radiating to her jaw. Her history is notable for hypertension, diabetes mellitus, and alcohol abuse. She has a 30 pack-year smoking history and takes lisinopril and metformin but has an allergy to aspirin. Her temperature is 99.1°F (37.3°C), blood pressure is 150/90 mmHg, pulse is 120/min, and respirations are 22/min. Physical examination reveals a diaphoretic and distressed woman. An electrocardiogram reveals ST elevations in leads I, aVL, and V5-6. She is admitted with plans for immediate transport to the catheterization lab for stent placement. What is the mechanism of the next medication that should be given to this patient?

Vitamin K epoxide reductase inhibitor

A 45-year-old man presents to the emergency department because of fever and scrotal pain for 2 days. Medical history includes diabetes mellitus and morbid obesity. His temperature is 40.0°C (104.0°F), the pulse is 130/min, the respirations are 35/min, and the blood pressure is 90/68 mm Hg. Physical examination shows a large area of ecchymosis, edema, and crepitus in his perineal area. Fournier gangrene is suspected. A right internal jugular central venous catheter is placed without complication under ultrasound guidance for vascular access in preparation for the administration of vasopressors. Which of the following is the most appropriate next step?

Obtain an immediate portable chest radiograph to evaluate line placement

Confirm line placement by ultrasound

Begin to use the line after documenting the return of dark, non-pulsatile blood from all ports

Begin infusion of normal saline through a central line

Begin infusion of norepinephrine to maintain systolic blood pressure over 90 mm Hg

DVT risk assessment for USMLE Step 1: High-Yield Surgery Lessons

Virchow's Triad - The Clotting Trinity

Three core factors that predispose to thrombosis. 📌 Mnemonic: SHE

Stasis of Blood Flow
- Immobilization (post-op), prolonged travel
- Heart failure, atrial fibrillation, venous obstruction
Hypercoagulability
- Malignancy (e.g., pancreatic, lung)
- Pregnancy, estrogen therapy
- Inherited thrombophilias (e.g., Factor V Leiden)
Endothelial Injury
- Surgery, trauma, catheter placement
- Atherosclerosis, vasculitis

⭐ High-Yield: Factor V Leiden is the most common inherited cause of hypercoagulability in Caucasian populations, leading to resistance to activated protein C.

DVT Risk Factors - Spotting the Danger

Virchow's Triad and associated conditions

Risk is classically stratified by Virchow's Triad:

Venous Stasis
- Immobilization (post-op, paralysis, prolonged travel >4 hrs)
- Obesity (BMI >30)
- Heart failure (decompensated)
- Advanced age
Hypercoagulability
- Malignancy (especially pancreatic, lung, hematologic)
- Pregnancy & postpartum period (up to 6 weeks)
- Estrogen therapy (OCPs, HRT)
- Inherited thrombophilias (e.g., Factor V Leiden)
- Sepsis & inflammatory states
Endothelial Injury
- Surgery (highest risk: orthopedic, pelvic, major abdominal)
- Trauma (fractures, direct vessel injury)
- Central venous catheters
- Smoking

⭐ High-Yield: The single strongest predictor for developing a VTE is a personal history of a prior DVT or pulmonary embolism.

Caprini Score - Quantifying the Risk

A cumulative risk assessment model to estimate postoperative VTE risk and guide prophylaxis. Points are assigned for individual risk factors.

1 Point Factors
- Age 41-60 yrs, BMI >25, minor surgery, varicose veins, pregnancy/postpartum, OCP/HRT
2 Point Factors
- Age 61-74 yrs, major open surgery (>45 min), laparoscopic surgery (>45 min), bed rest >72 hrs
3 Point Factors
- Age ≥75 yrs, personal or family hx of VTE, Factor V Leiden, Prothrombin 20210A
5 Point Factors
- Elective major lower extremity arthroplasty, hip/pelvis/leg fracture, stroke (<1 mo), multiple trauma

Caprini Score for Venous Thromboembolism Risk Assessment

Score	Risk Level	Recommended Prophylaxis
0-1	Low	Early ambulation
2	Moderate	Mechanical (SCDs)
3-4	High	LMWH/LDUH ± Mechanical
≥5	Highest	LMWH/LDUH + Mechanical

Risk-Based Prophylaxis - The Prevention Playbook

Goal: Match prophylaxis intensity to patient's thrombotic risk using a validated model.
Tool: Caprini Score for VTE Risk Assessment is a common standard.

⭐ Withhold LMWH for ≥12-24 hours before neuraxial anesthesia (e.g., epidural) and for >4 hours after catheter removal to minimize spinal hematoma risk.

Pharmacologic Options:
- LMWH: Enoxaparin 40 mg SC daily.
- UFH: 5000 units SC q8-12h.
Mechanical Options: Intermittent pneumatic compression (IPC) devices are superior to graduated compression stockings (GCS).

High-Yield Points - ⚡ Biggest Takeaways

The Wells score is the key clinical tool to estimate pre-test probability of DVT.

Major risk factors include prior VTE, active cancer, recent surgery or prolonged immobilization, and inherited thrombophilias.

A negative D-dimer is highly effective at ruling out DVT in patients with a low Wells score.

Compression ultrasonography is the first-line imaging test for confirming a DVT diagnosis.

Pharmacologic prophylaxis (e.g., LMWH) is crucial in high-risk surgical patients.

The Caprini score specifically tailors VTE prophylaxis recommendations for surgical patients.

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