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.

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.

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.

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.

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.

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.

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.

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.

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.

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.