What is the initial hemodialysis prescription for a patient with acute kidney injury and a 22 mm calculus in the right upper ureter without hydronephrosis?

Hemodialysis Prescription for AKI with Obstructive Ureteral Calculus

Before prescribing hemodialysis, you must first address the urologic obstruction—the 22 mm calculus requires urgent urologic intervention (percutaneous nephrostomy or ureteroscopy) as the primary treatment, with dialysis reserved only for life-threatening metabolic complications that cannot wait for stone removal.

Critical First Step: Assess for Absolute Indications

The decision to initiate emergent hemodialysis depends entirely on whether life-threatening complications are present, not simply on the presence of AKI 1:

Absolute Indications Requiring Emergent Dialysis:

• Severe hyperkalemia with ECG changes (peaked T waves, widened QRS, bradycardia, or asystole) 1, 2
• Severe metabolic acidosis with impaired respiratory compensation 1
• Pulmonary edema unresponsive to diuretics 1
• Uremic complications (encephalopathy, pericarditis, or bleeding) 1
• Severe symptomatic dysnatremia resistant to medical management 1

If none of these are present, dialysis should be deferred while the obstructive uropathy is urgently corrected 3, 4.

Initial Hemodialysis Prescription (If Emergent Dialysis Required)

Modality Selection:

For hemodynamically stable patients: Use intermittent hemodialysis, which provides faster correction of severe hyperkalemia 1, 5.

For hemodynamically unstable patients requiring vasopressors: Use continuous renal replacement therapy (CRRT) with CVVHDF or CVVH 6, 5.

Intermittent Hemodialysis Parameters (Stable Patients):

• Duration: 3-4 hours initially 3
• Blood flow rate: 300-400 mL/min
• Dialysate flow rate: 500-800 mL/min
• Target Kt/V: 3.9 per week (typically 1.2-1.4 per session for 3 sessions weekly) 1
• Dialysate composition: Bicarbonate-based (NOT lactate-based) 6, 1
• Potassium bath: 0-1 mEq/L if severe hyperkalemia; 2 mEq/L for maintenance 1
• Calcium bath: 2.5 mEq/L
• Ultrafiltration rate: Limit to <13 mL/kg/hour to avoid intradialytic hypotension and further renal injury 7

CRRT Parameters (Unstable Patients):

• Modality: CVVHDF (continuous venovenous hemodiafiltration) 6, 5
• Effluent dose: 20-25 mL/kg/hour 6, 1, 5
• Replacement fluid: Bicarbonate-based 6, 1
• Anticoagulation: Regional citrate anticoagulation preferred if no contraindications 1, 5

Vascular Access:

• Use uncuffed non-tunneled dialysis catheter 1, 5
• Preferred sites (in order): Right internal jugular vein > femoral vein > left internal jugular vein > subclavian vein (last choice due to stenosis risk) 5
• Always use ultrasound guidance for insertion 5

Critical Management Pitfalls to Avoid:

Do NOT delay urologic decompression: The 22 mm stone in the upper ureter is the root cause of AKI. Even without hydronephrosis on initial imaging, obstruction may be present or developing 2. Dialysis treats complications but does not address the underlying problem 3, 4.

Monitor for refractory hyperkalemia: Large obstructive stones can cause "reversed intraperitoneal dialysis" if kidney rupture occurs, leading to therapy-resistant hyperkalemia requiring emergency dialysis 2.

Avoid aggressive ultrafiltration: Excessive fluid removal and hypotension during dialysis can cause further kidney injury and reduce likelihood of renal recovery 7, 6.

Discontinue nephrotoxic medications: NSAIDs, aminoglycosides, contrast agents, and ACE inhibitors should be stopped 3, 4.

Monitoring During Dialysis:

• Continuous ECG monitoring if hyperkalemia present 2
• Hourly vital signs and assessment for hypotension 7
• Electrolytes and acid-base status every 2-4 hours initially 6, 5
• Pre- and post-dialysis weights 7
• Urine output monitoring (if any residual function) 7

Post-Dialysis Plan:

Coordinate immediate urologic intervention for stone removal via ureteroscopy, percutaneous nephrostomy, or extracorporeal shockwave lithotripsy 8, 2.

Reassess need for ongoing dialysis after obstruction is relieved—many patients will recover kidney function once the stone is removed 4, 9.

If dialysis continues beyond 14 days: Assess for renal recovery weekly with pre-dialysis creatinine and residual kidney function measurements 6.