Continuous Renal Replacement Therapy (CRRT) for Acute Kidney Injury

Indications and Modalities

• The American College of Physicians recommends initiating CRRT immediately when life-threatening changes in fluid, electrolyte, and acid-base balance exist in patients with acute kidney injury (AKI) 1
• CRRT is specifically indicated for hemodynamically unstable patients requiring vasopressor support, patients with acute brain injury or increased intracranial pressure, patients with severe fluid overload unresponsive to diuretics, and patients on extracorporeal life support (ECLS) such as ECMO 2, 3

Absolute Indications for Emergent Dialysis

• Severe hyperkalemia or rapidly rising potassium levels with ECG changes require emergent dialysis 1
• Severe symptomatic dysnatremia resistant to medical management, severe metabolic acidosis with impaired compensation, pulmonary edema or severe fluid overload causing respiratory compromise, and uremic complications (encephalopathy, pericarditis, bleeding) are absolute indications for emergent dialysis 1

CRRT Modality Selection

• CVVHDF or CVVH are preferred for hemodynamically unstable patients, as recommended by the American Society of Nephrology 2
• Intermittent hemodialysis may be considered for rapid correction of severe hyperkalemia in hemodynamically stable patients 1

Technical Aspects of CRRT Implementation

• The International Society of Nephrology recommends delivering an effluent volume of 20-25 mL/kg/h for all CRRT modalities 2, 3
• Bicarbonate-based replacement fluids are preferred over lactate-based solutions, especially in patients with shock, liver failure, or lactic acidemia, as recommended by the European Renal Association 2, 3

Monitoring and Assessment During CRRT

• Regular assessment of electrolytes, acid-base status, and fluid balance is essential, as recommended by the National Kidney Foundation 3
• Kidney recovery is defined as sustained independence from RRT for a minimum of 14 days, according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 4, 5

Transitioning from CRRT to Intermittent Modalities

• The American Society of Nephrology recommends considering transitioning from CRRT to intermittent hemodialysis when vasopressor support has been discontinued, hemodynamic stability has been achieved, intracranial hypertension has resolved, and fluid balance can be adequately controlled by intermittent hemodialysis 3

Special Considerations

• The National Institute of Diabetes and Digestive and Kidney Diseases recommends frequent review of kidney function for patients discharged while still receiving RRT, with weekly assessment of pre-dialysis serum creatinine values and regular assessment of residual kidney function 4, 5
• Avoiding excessive fluid removal and hypotension can prevent re-injury to the kidney and enhance likelihood of renal recovery, as recommended by the American College of Physicians 4, 5

Management of Euglycemic DKA in Patients on CRRT

Core Principle: Treat the Metabolic Emergency

• The American Journal of Kidney Diseases recommends abandoning the standard DKA fluid resuscitation approach in favor of CRRT-guided fluid management in patients with euglycemic DKA on CRRT 6

Critical Modifications Required for CRRT Patients

Fluid Management Considerations

• The American Journal of Kidney Diseases suggests that CRRT already provides precise fluid balance control, and fluid administration should be coordinated with CRRT prescription to avoid volume overload, and the standard DKA fluid resuscitation approach must be abandoned in favor of CRRT-guided fluid management 6

Bicarbonate and Acid-Base Management

• The American Journal of Kidney Diseases recommends using bicarbonate-based CRRT replacement fluids rather than lactate-based solutions in patients with euglycemic DKA on CRRT 7

Special Consideration for Citrate Anticoagulation

• The American Journal of Kidney Diseases notes that regional citrate anticoagulation for CRRT can affect acid-base status interpretation, and citrate metabolism generates bicarbonate, potentially masking ongoing ketoacidosis 7
• The American Journal of Kidney Diseases recommends monitoring ionized calcium and total calcium/ionized calcium ratio to detect citrate accumulation in patients with euglycemic DKA on CRRT with regional citrate anticoagulation 7
• The American Journal of Kidney Diseases suggests that CRRT should be continued based on renal indications independent of DKA resolution, and transition to subcutaneous insulin should only occur after metabolic parameters normalize and patient tolerates oral intake 6

Renal Replacement Therapy and Renal Function Assessment

Limitations of Renal Function Evaluation During TRR

• The ADQI consensus guidelines state that current tools and diagnostics are insufficient to accurately assess renal function in patients receiving acute TRR 8, 9, 10
• Serum creatinine is artificially reduced by dialysis, not by renal recovery 8, 9
• Muscle mass loss during critical illness further reduces creatinine, independent of renal function 9, 10

Appropriate Renal Function Evaluation

• The KDIGO guidelines recommend a 24-hour urine collection to measure urine volume and creatinine/urea clearance to assess residual renal function 8, 10
• Alternative markers, such as cystatin C (not affected by muscle mass) or direct measurement of GFR with iohexol clearance, should be considered 9, 10, 11
• Renal recovery is defined as sustained independence from TRR for >14 days, not just normal creatinine values 8, 9

Clinical Context: Initiating TRR

• The KDIGO guidelines and the Canadian Society of Nephrology state that the decision to initiate TRR should not be based solely on absolute creatinine or BUN values 12
• Absolute indications for TRR include severe hyperkalemia with ECG changes, pulmonary edema with respiratory compromise, severe metabolic acidosis, and uremic complications (encephalopathy, pericarditis) 12

Common Pitfall to Avoid

• Assuming renal recovery based on normal creatinine or BUN values during TRR is incorrect; true renal recovery requires sustained independence from TRR, evaluation of residual renal function, and ongoing nephrologic follow-up 8, 10

CRRT Initiation and Management in Hemodynamically Unstable Critically Ill Patients

Indications for Starting CRRT

• Initiate CRRT immediately in hemodynamically unstable patients with acute kidney injury (AKI) who have life‑threatening metabolic derangements; it is preferred over intermittent hemodialysis when vasopressor support, acute brain injury, or severe fluid overload unresponsive to diuretics is present【13】.
• Absolute emergent indications include diuretic‑unresponsive pulmonary edema causing respiratory compromise and uremic complications such as encephalopathy, pericarditis, or bleeding【14】.
• Do not wait for conventional chronic kidney disease laboratory thresholds (e.g., BUN or creatinine) before starting CRRT, because metabolic complications develop more rapidly in critically ill patients【14】.

Vascular Access Strategy

• First‑choice access is the right internal jugular vein; the femoral vein is second choice (avoid in patients with high body‑mass index), the left internal jugular vein third, and the subclavian vein is a last resort due to higher thrombosis/stenosis risk【15】.
• For acute initiation, use an uncuffed non‑tunneled dialysis catheter of appropriate length and gauge; consider a cuffed catheter if prolonged renal replacement therapy is anticipated【13】.

Anticoagulation

• Regional citrate anticoagulation is the first‑line strategy for patients without contraindications, offering longer filter life and lower bleeding risk compared with systemic heparin【13】.

Effluent Dose Prescription

• Prescribe an effluent dose of 20–25 mL/kg/h for all CRRT modalities; because delivered dose is usually lower than prescribed, the prescription should be set higher to compensate for downtime and interruptions【13】.

Fluid Composition and Buffer Selection

• Use bicarbonate‑based replacement fluids rather than lactate‑based solutions in patients with shock, liver failure, or lactic acidosis, as bicarbonate avoids worsening acidosis in these settings【15】.
• Lactate‑containing solutions should be reserved for hemodynamically stable patients without liver dysfunction or lactic acidosis【15】.
• Maintain physiologic electrolyte concentrations and avoid supra‑physiologic glucose levels to prevent hyperglycemia【15】.
• Pre‑dilution of replacement fluid can enhance ultrafiltration rates and reduce filter clotting【15】.

Hemodynamic Management During CRRT

• CRRT provides superior hemodynamic tolerance compared with intermittent modalities; however, avoid excessive fluid removal that may cause hypotension and impede renal recovery【15】.
• Maintaining a negative fluid balance (especially in acute lung injury) shortens ICU length of stay, while volume overload is associated with adverse outcomes【15】.
• Use integrated fluid‑balancing systems specifically designed for CRRT rather than adapted intravenous pumps, to reduce the risk of delivery errors【15】.

Monitoring Requirements

• Perform regular monitoring of electrolytes, acid‑base status, fluid balance, and filter performance; particular vigilance is needed for CRRT‑induced hypokalemia and hypophosphatemia, especially with high‑dose or prolonged therapy【15】.

Transition and Discontinuation Criteria

• Consider transitioning from CRRT to intermittent hemodialysis when vasopressor support has been discontinued, hemodynamic stability is achieved, intracranial hypertension (if present) has resolved, and fluid balance can be managed with intermittent therapy【13】.
• Continue CRRT while criteria defining severe AKI are present; discontinue when kidney function has recovered or when renal replacement therapy no longer aligns with the patient’s overall care goals【14】【13】.

Special Considerations for Patients on Extracorporeal Life Support (ECMO/VAD)

• Integrate CRRT with ECMO to prevent fluid overload that can impair ECMO performance; implementation should be based on institutional expertise and available technology【13】.

Clinical Decision‑Making for Initiation of Renal Replacement Therapy in ARDS

Assessment Criteria (American Journal of Kidney Diseases)

• Initiation of renal replacement therapy (RRT) should be guided by a comprehensive clinical assessment rather than waiting for specific urea or creatinine thresholds. The decision relies on overall patient status, including hemodynamics, fluid balance, and organ dysfunction, as recommended by the American Journal of Kidney Diseases. 16

• Modifiable conditions that can be addressed by RRT—such as refractory fluid overload, severe electrolyte disturbances, or metabolic acidosis—must be identified and prioritized in the clinical evaluation. This approach is supported by the American Journal of Kidney Diseases. 16

• Trends in laboratory parameters (e.g., rising azotemia) are more informative than isolated single values when deciding to start RRT; clinicians should monitor the trajectory of these markers rather than fixed cut‑offs. This recommendation originates from the American Journal of Kidney Diseases. 16

Indications for Initiating Dialysis in Acute Kidney Injury (AKI)

Emergent (Absolute) Indications

• Initiate renal replacement therapy immediately when any life‑threatening metabolic complication is present—severe hyperkalemia with ECG changes, pulmonary edema causing respiratory compromise unresponsive to diuretics, severe metabolic acidosis (arterial pH < 7.25 or bicarbonate < 10 mmol/L), or uremic complications such as encephalopathy, pericarditis, or bleeding. KDIGO recommends this emergent approach. 17

Relative (Delayed/Standard) Indications

• In the absence of absolute indications, KDIGO advises a delayed/standard strategy because early dialysis has not shown survival benefit and may cause harm. 17
• KDIGO Stage 3 AKI (creatinine ≥ 3 × baseline or ≥ 4.0 mg/dL with an acute rise ≥ 0.3 mg/dL) that persists despite correction of reversible factors qualifies as a relative indication for dialysis. 17
• Progressive oliguria defined as urine output < 0.3 mL/kg/h for ≥ 24 hours that does not improve with fluid optimization is a relative indication. 17
• Refractory volume overload despite maximal diuretic therapy in a hemodynamically stable patient is a relative indication. 17

Criteria for Delaying Dialysis (When No Absolute Indication Exists)

• Postpone initiation until Stage 3 AKI persists for > 48 hours despite optimal management of reversible causes. 17
• Delay until the patient’s metabolic demands exceed renal capacity, as judged by ongoing clinical deterioration (e.g., worsening azotemia, rising BUN, or worsening acid‑base status). 17

Modality Selection for Hemodynamically Unstable Patients

• Continuous renal replacement therapy (CRRT) is preferred for patients who are hemodynamically unstable, require vasopressor support, have acute brain injury/increased intracranial pressure, or have severe fluid overload. KDIGO endorses CRRT in these settings. 17
• The recommended effluent (dialysate) flow for CRRT is 20–25 mL/kg/h to ensure adequate solute clearance. 17
• Although CRRT offers physiological advantages over intermittent hemodialysis for unstable patients, randomized trials have not demonstrated a survival difference. 17