A 78-year-old man dies suddenly from complications of acute kidney failure. An autopsy is performed and microscopic evaluation of the kidneys shows pale, swollen cells in the proximal convoluted tubules. Microscopic evaluation of the liver shows similar findings. Which of the following is the most likely underlying mechanism of these findings?

Impaired Na+/K+-ATPase pump activity

Cytoplasmic triglyceride accumulation

A 22-year-old man is brought to the emergency department by ambulance 1 hour after a motor vehicle accident. He did not require any circulatory resuscitation at the scene, but he was intubated because he was unresponsive. He has no history of serious illnesses. He is on mechanical ventilation with no sedation. His blood pressure is 121/62 mm Hg, the pulse is 68/min, and the temperature is 36.5°C (97.7°F). His Glasgow coma scale (GCS) is 3. Early laboratory studies show no abnormalities. A search of the state donor registry shows that he has registered as an organ donor. Which of the following is the most appropriate next step in evaluation?

Evaluation of brainstem reflexes

A 52-year-old man is brought to the emergency department by ambulance after a motor vehicle accident. He was an unrestrained passenger who was ejected from the vehicle. On presentation, he is found to be actively bleeding from numerous wounds. His blood pressure is 76/42 mmHg and pulse is 152/min. Attempts at resuscitation fail, and he dies 25 minutes later. Autopsy shows blood in the peritoneal cavity, and histology of the kidney reveals swelling of the proximal convoluted tubule epithelial cells. Which of the following is most likely the mechanism underlying the renal cell findings?

Decreased function of the Na+/K+-ATPase

Decreased activity of caspase 7

Increased activity of caspase 9

Increased function of the Na+/K+-ATPase

Increased activity of caspase 8

A 45-year-old female is undergoing renal transplantation for management of chronic renal failure secondary to glomerulonephritis. The transplant surgeon placed the donor kidney in the recipient and anastomosed the donor renal artery to the recipient's external iliac artery as well as the donor ureter to the recipient's bladder. After removing the clamps on the external iliac artery, the recipient's blood is allowed to perfuse the transplanted kidney. Within 3 minutes, the surgeon notes that the kidney does not appear to be sufficiently perfused. Upon further investigation, an inflammatory reaction is noted that led to clotting off of the donor renal artery, preventing blood flow to the transplanted organ. Which of the following best describes the pathophysiology of this complication?

Type III hypersensitivity reaction

Type IV hypersensitivity reaction

Type I hypersensitivity reaction

A 38-year-old kidney transplant recipient maintained on tacrolimus presents with a 2-week history of progressive confusion, ataxia, and visual disturbances. MRI shows multifocal white matter lesions without mass effect or enhancement. CSF analysis reveals mild pleocytosis with elevated protein. JC virus DNA is detected in CSF by PCR. Serum tacrolimus level is therapeutic at 8 ng/mL. Apply knowledge of this condition to determine the appropriate management strategy.

Significantly reduce or discontinue immunosuppression and provide supportive care

Switch from tacrolimus to sirolimus to preserve graft while treating infection

Continue current immunosuppression and administer IVIG therapy

Maintain immunosuppression and start cidofovir antiviral therapy

Reduce tacrolimus by 50% and start high-dose corticosteroids

A 41-year-old heart transplant recipient (5 years post-transplant) on cyclosporine, azathioprine, and prednisone develops progressive dyspnea on exertion. Echocardiogram shows preserved ejection fraction but abnormal diastolic dysfunction. Right heart catheterization reveals elevated filling pressures. Endomyocardial biopsy shows interstitial fibrosis without significant cellular infiltration. Coronary angiography shows diffuse, concentric narrowing of distal vessels. Synthesize these findings to determine the underlying pathophysiology and evaluate management options.

Cardiac allograft vasculopathy requiring consideration for retransplantation evaluation

Restrictive cardiomyopathy from previous rejection episodes requiring diuretic therapy

Drug-induced cardiomyopathy from calcineurin inhibitor toxicity requiring switch to mTOR inhibitor

Acute cellular rejection requiring pulse steroids and optimization of immunosuppression

Antibody-mediated rejection requiring plasmapheresis and rituximab therapy

A 52-year-old man with hepatocellular carcinoma (single 4.5 cm lesion) within Milan criteria is listed for liver transplantation with MELD exception points. While waiting, alpha-fetoprotein increases from 125 to 850 ng/mL over 3 months despite locoregional therapy. Repeat imaging shows the tumor has grown to 6 cm with possible vascular invasion. He has no extrahepatic disease. His wife offers to be a living donor. Synthesize the clinical data and evaluate the most appropriate management decision.

Remove from transplant list and pursue systemic therapy with sorafenib

Perform surgical resection then relist if recurrence occurs within criteria

Downstage with aggressive locoregional therapy then reassess for transplantation

Proceed with living donor transplantation given no extrahepatic disease

Continue locoregional therapy and maintain listing with exception points

Organ preservation techniques for USMLE Step 2 CK: High-Yield Surgery Lessons

Ischemia & Reperfusion - 🕒 Beating the Clock

Ischemic Phase: Lack of O₂ leads to anaerobic metabolism. Key events:
- ↓ ATP production
- ↑ Intracellular Na⁺ & Ca²⁺ (cellular swelling)
- Accumulation of metabolic byproducts (e.g., hypoxanthine)
Reperfusion Phase: Restoration of blood flow paradoxically triggers injury.

Ischemia-Reperfusion Injury Pathophysiology

⭐ The enzyme Xanthine Oxidase is a major source of Reactive Oxygen Species (ROS) upon reperfusion. Drugs like Allopurinol inhibit this enzyme, mitigating reperfusion injury.

Preservation Solutions - 🍹 The Magic Kool-Aid

Goal: Minimize ischemic injury during transport by reducing metabolic demand and preventing cellular damage.
Key Ingredients & Actions:
- Buffers (e.g., Phosphate): Combat acidosis from anaerobic metabolism.
- Impermeants (e.g., Lactobionate, Mannitol): Act as osmotic agents to prevent cell swelling.
- Antioxidants (e.g., Glutathione, Allopurinol): Neutralize oxygen free radicals, mitigating reperfusion injury.
- ATP Precursors (e.g., Adenosine): Provide substrate for energy regeneration post-transplant.
Common Solutions:
- UW (Viaspan): High K+, low Na+ (intracellular type). Gold standard for abdominal organs.
- HTK Solution: Low K+, high Na+ (extracellular type). Common for kidney and thoracic organs.

⭐ All preservation solutions rely on hypothermia. Cooling organs to ~4°C reduces metabolic rate by over 90%, extending viability.

Preservation Methods - 🥶 Chillin' vs. Pumpin'

Goal: ↓ organ metabolism to minimize ischemia-reperfusion injury. Target temp: ~4°C.

Feature	Static Cold Storage (SCS)	Hypothermic Machine Perfusion (HMP)
Mechanism	Flush & submerge in cold solution	Continuous pulsatile/non-pulsatile flow
Complexity	Simple, low-cost	Complex, resource-intensive
Monitoring	None	Real-time pressure, flow, resistance
Best For	Standard criteria donors, short cold times	Extended criteria donors (ECD), DCD, longer times

⭐ HMP is superior for extended criteria donor kidneys, as it ↓ rates of delayed graft function (DGF) and improves graft survival compared to SCS.

High‑Yield Points - ⚡ Biggest Takeaways

Static cold storage (SCS) with Viaspan (UW solution) is the most common method, using hypothermia (~4°C) to decrease metabolic demand.

Hypothermic machine perfusion (HMP) improves organ quality by continuously circulating cold preservation fluid, reducing ischemia-reperfusion injury.

The primary goal is to prevent ATP depletion and minimize warm ischemia time.

Maximum cold ischemia times vary: Kidneys (24-36h) > Liver (8-12h) > Heart/Lungs (4-6h).

Poor preservation is a key risk factor for Primary Graft Dysfunction (PGD).

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