Renal Replacement Therapy And Urologic Complications - USMLE Step 2

1. In addition to intravenous fluid resuscitation and broad-spectrum antibiotics, which of the following is the most urgent intervention?
   Answer: Ureteral stent placement This patient has an obstructing kidney stone complicated by infection (obstructive pyelonephritis), which is a urologic emergency. The infection cannot be cleared effectively in the presence of an obstruction. Therefore, urgent decompression of the urinary tract is required. This is accomplished by either placing a ureteral stent via cystoscopy or a percutaneous nephrostomy tube. Definitive stone treatment like ESWL is contraindicated in the setting of an active infection and is performed after the infection has been controlled.
2. Which of the following is the most appropriate next step in managing this patient's catheter?
   Answer: Remove the catheter and place a new one at a different site The patient has a suspected catheter-related bloodstream infection (CRBSI). In patients with a tunneled dialysis catheter and signs of sepsis, prompt removal of the catheter is indicated in addition to systemic antibiotics. Waiting for culture results can lead to delays in source control and worse outcomes. Guidewire exchange is not recommended for CRBSI because it does not eradicate the infection along the subcutaneous tract. A new temporary catheter should be placed at a different site until the infection is cleared.
3. Which of the following is the most appropriate next step in management?
   Answer: Remove the peritoneal dialysis catheter and initiate hemodialysis Refractory peritonitis, defined as failure to improve after 5 days of appropriate antibiotic therapy, is a key indication for removal of the peritoneal dialysis catheter. Continuing PD in this setting can lead to severe complications, including abscess formation and encapsulating peritoneal sclerosis. The source of the infection (the catheter) must be removed. The patient will need to be transitioned to hemodialysis, usually via a temporary central venous catheter, until the infection resolves and a decision can be made about future RRT.
4. The primary purpose of the ultrasound with Doppler in this setting is to rule out which of the following complications?
   Answer: Urinary obstruction or vascular thrombosis In the immediate post-transplant period, a sudden rise in creatinine and decrease in urine output should prompt evaluation for surgical or technical complications. A renal ultrasound with Doppler is the initial imaging test of choice to assess for urologic complications like ureteral obstruction (which would show hydronephrosis) and vascular complications like renal artery or vein thrombosis (which would show abnormal blood flow). While acute rejection, drug toxicity, and viral nephropathy are on the differential for allograft dysfunction, they are diagnoses of exclusion after ruling out these urgent mechanical and vascular problems.
5. Compared to a patient on standard in-center hemodialysis, a patient on continuous ambulatory peritoneal dialysis is at a significantly higher risk for which of the following metabolic disturbances?
   Answer: Hyperglycemia and hypertriglyceridemia Peritoneal dialysis utilizes a dialysate solution containing high concentrations of dextrose to create an osmotic gradient for fluid removal (ultrafiltration). The continuous absorption of this glucose load across the peritoneal membrane can lead to significant hyperglycemia, weight gain, and hypertriglyceridemia. In contrast, hemodialysis is intermittent, and problems like hyperkalemia and metabolic acidosis are more likely to build up between sessions. Both modalities manage calcium and phosphate levels, but the glucose load is a unique and prominent feature of PD.
6. This patient's condition is most likely caused by which of the following mechanisms?
   Answer: Cerebral edema from a rapid decrease in plasma osmolality This patient is experiencing dialysis disequilibrium syndrome (DDS), a neurologic complication that occurs most often in patients undergoing their first few dialysis treatments, especially when the pre-dialysis BUN is very high. Hemodialysis removes urea from the blood much faster than it can be cleared from the brain. This creates an osmotic gradient that pulls water into the brain, causing cerebral edema, increased intracranial pressure, and the resulting neurologic symptoms. It is prevented by using shorter, less efficient dialysis sessions initially.
7. This patient's condition is most likely due to the deposition of which of the following substances?
   Answer: Beta-2 microglobulin This clinical picture is characteristic of dialysis-related amyloidosis, a long-term complication of hemodialysis. It is caused by the accumulation and deposition of beta-2 microglobulin, a protein that is poorly cleared by conventional dialysis membranes. Deposition in osteoarticular structures leads to scapulohumeral periarthritis (shoulder pain), carpal tunnel syndrome, and destructive spondyloarthropathy. The risk increases significantly with the duration of dialysis.
8. Which of the following is the most appropriate next step in management?
   Answer: Urgent ureteroscopy with stent placement This patient has an obstructing kidney stone that is large (>10 mm) and is associated with signs of severe obstruction (severe hydronephrosis), acute kidney injury, and hemodynamic instability (hypotension, tachycardia likely due to dehydration and pain/vasovagal response). These are indications for urgent urologic intervention to relieve the obstruction. Ureteroscopy allows for direct visualization of the stone, its removal (e.g., with a laser), and placement of a stent to ensure drainage. Medical expulsive therapy is not appropriate for large stones or complicated presentations. ESWL is less effective for proximal ureteral stones and is not typically performed emergently.
9. Which of the following is the most likely diagnosis?
   Answer: Encapsulating peritoneal sclerosis Encapsulating peritoneal sclerosis (EPS) is a rare but serious complication of long-term peritoneal dialysis. It involves the formation of a dense fibrocollagenous membrane that encases the small bowel, leading to chronic inflammation and symptoms of bowel obstruction, including nausea, vomiting, pain, and malnutrition. The greatest risk factor is the duration of peritoneal dialysis. His presentation is subacute/chronic, making acute issues like volvulus or ischemic colitis less likely, and the absence of fever or cloudy fluid argues against typical peritonitis.
10. Which of the following is the most appropriate management for this patient's high urine output?
    Answer: Intravenous replacement of urinary losses with 0.45% saline This patient is experiencing post-obstructive diuresis, a polyuric phase that follows the relief of a prolonged bilateral urinary tract obstruction. It is driven by an osmotic diuresis from retained urea and other solutes, as well as impaired tubular concentrating ability. The massive fluid and electrolyte loss can lead to severe volume depletion, hypotension, and electrolyte abnormalities. Management involves careful monitoring and replacement of a portion (e.g., 50-75%) of the urinary losses with intravenous fluids, typically hypotonic saline (0.45% saline) to avoid hypernatremia.
11. Which of the following findings is the most absolute and urgent indication for initiating renal replacement therapy?
    Answer: Pericardial friction rub All the listed options are indications for urgent renal replacement therapy (the 'AEIOU' mnemonic: Acidosis, Electrolytes, Intoxication, Overload, Uremia). However, uremic pericarditis, manifested by a pericardial friction rub, is considered an absolute and life-threatening indication that requires immediate dialysis to prevent progression to cardiac tamponade. While severe hyperkalemia with ECG changes is also a medical emergency requiring immediate treatment (including dialysis), the development of pericarditis signifies a severe systemic uremic state that must be addressed without delay.
12. Which of the following is the most appropriate next step in management?
    Answer: Placement of bilateral percutaneous nephrostomy tubes This patient has anuric acute kidney injury due to bilateral ureteral obstruction, likely from her metastatic cancer. Since a Foley catheter did not relieve the obstruction, the blockage is located in the upper urinary tract (ureters). The definitive and urgent treatment is to bypass the obstruction and decompress the collecting systems. This is achieved with bilateral percutaneous nephrostomy tubes or ureteral stents. While she has hyperkalemia that needs treatment (calcium gluconate, insulin), the underlying cause must be addressed. Hemodialysis may be required, but relieving the obstruction is the primary intervention.
13. Which of the following is the most appropriate imaging study to confirm the diagnosis?
    Answer: Non-contrast helical CT of the abdomen and pelvis The patient's presentation is classic for nephrolithiasis. A non-contrast helical CT scan of the abdomen and pelvis is the gold standard for diagnosing kidney stones. It is highly sensitive and specific for detecting stones of all types and sizes, and can also identify signs of obstruction like hydronephrosis. A KUB can miss radiolucent stones (e.g., uric acid stones). Renal ultrasound is good for detecting hydronephrosis but is less sensitive for identifying ureteral stones. Intravenous pyelogram has been largely replaced by CT due to risks of contrast nephropathy and lower diagnostic accuracy.
14. Which of the following is the most likely diagnosis?
    Answer: Dialysis access-associated steal syndrome This patient's symptoms are classic for dialysis access-associated steal syndrome. The high flow through the arteriovenous fistula shunts an excessive amount of blood away from the distal extremity, causing ischemia, particularly when the fistula flow is at its maximum during dialysis. Symptoms include pain, coolness, pallor, and paresthesias. Fistula thrombosis would present with loss of the thrill and bruit. Central venous stenosis typically causes swelling of the entire arm. Carpal tunnel syndrome would not typically cause coolness and pallor.
15. Which of the following is the most appropriate management for this patient?
    Answer: Medical expulsive therapy For small (<10 mm), uncomplicated ureteral stones, medical expulsive therapy is the first-line treatment. This typically includes adequate hydration, pain control with NSAIDs, and an alpha-blocker like tamsulosin to relax the ureteral smooth muscle and facilitate stone passage. Invasive procedures like ESWL or ureteroscopy are reserved for larger stones, uncontrolled pain, or signs of obstruction or infection. A nephrostomy tube is an intervention for severe obstruction and is not indicated here.
16. Which of the following is the most suitable long-term renal replacement therapy for this patient?
    Answer: Peritoneal dialysis Peritoneal dialysis (PD) is an excellent option for motivated patients who want to manage their own care and maintain a flexible lifestyle. It can be performed at home, which aligns with her desire to minimize facility visits. Her lack of prior abdominal surgeries makes her a good candidate. In-center hemodialysis requires travel to a dialysis unit three times a week. While transplantation is the ultimate goal, it is not an immediate option and requires a suitable donor and extensive workup. Nocturnal HD is less common and still requires travel to a center.
17. Which of the following is the most appropriate initial step in management?
    Answer: Insert a Foley catheter This patient presents with acute urinary retention secondary to benign prostatic hyperplasia, leading to postrenal acute kidney injury. The most appropriate initial step is to relieve the obstruction, which is both diagnostic and therapeutic. Insertion of a Foley catheter will decompress the bladder, alleviate the patient's symptoms, and allow for recovery of renal function. Ultrasound would be the next step if catheterization is unsuccessful or if an upper tract obstruction is suspected. Tamsulosin is used for chronic management but is not the initial treatment for acute retention. Hemodialysis is not indicated unless there are life-threatening complications of renal failure that persist after the obstruction is relieved.
18. Which of the following is the most appropriate immediate action?
    Answer: Administer a bolus of intravenous normal saline Intradialytic hypotension is the most common complication of hemodialysis, typically caused by rapid removal of fluid (ultrafiltration) exceeding the plasma refilling rate. The immediate management is to decrease or temporarily stop ultrafiltration and administer an intravenous bolus of isotonic saline to restore intravascular volume. Increasing the ultrafiltration rate would worsen the hypotension. Midodrine is used for prevention, not acute treatment. Stopping the session is a last resort if the patient does not respond to initial measures.
19. Which of the following is the most appropriate treatment for this patient's kidney stone?
    Answer: Percutaneous nephrolithotomy Large, complex stones, such as staghorn calculi (>2 cm) filling the renal pelvis and calyces, require surgical removal. Percutaneous nephrolithotomy (PCNL) is the treatment of choice for these stones. This procedure involves creating a tract from the skin directly into the kidney to allow for fragmentation and removal of the stone. ESWL and ureteroscopy are less effective for such a large stone burden and are associated with lower stone-free rates and the need for multiple procedures. Medical therapy is not effective for stones of this size.
20. After sending a sample of the peritoneal fluid for analysis, which of the following is the most appropriate next step?
    Answer: Administer empiric intraperitoneal antibiotics The clinical presentation is highly suggestive of PD-associated peritonitis. The standard of care is to promptly initiate empiric intraperitoneal antibiotics after obtaining a fluid sample for cell count, Gram stain, and culture. Intraperitoneal administration achieves high local concentrations and is more effective than intravenous administration for this condition. Catheter removal is reserved for refractory or fungal peritonitis. A CT scan is not necessary for the initial diagnosis.

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