Acute Kidney Injury in the ICU - CRRT vs Intermittent Dialysis

Key Points

• Start renal replacement therapy for refractory complications of kidney failure, not for creatinine elevation alone.
• Major indications include refractory hyperkalemia, severe acidemia, pulmonary edema or fluid overload, selected toxins, and uremic complications.
• CRRT is generally favored in hemodynamically unstable patients and when abrupt osmotic shifts could worsen cerebral edema.
• Intermittent hemodialysis is efficient for stable patients who need rapid solute or fluid removal.
• SLED is a hybrid option used in some ICUs.
• The modality can change as the patient stabilizes; neither CRRT nor intermittent dialysis is universally superior.
• Review medication dosing because CRRT and intermittent dialysis clear drugs differently.

Algorithm

1. Identify and treat reversible AKI causes, including hypoperfusion, obstruction, sepsis, and nephrotoxins.
2. Determine whether a definitive dialysis indication is present and refractory to medical therapy.
3. Assess hemodynamic stability, intracranial pressure concerns, fluid-removal requirement, and desired speed of solute clearance.
4. Choose CRRT for unstable patients or when gradual fluid and osmotic shifts are preferred.
5. Choose intermittent hemodialysis for stable patients requiring efficient rapid clearance.
6. Use SLED when a prolonged intermittent strategy best fits physiology and local resources.
7. Monitor delivered dose, electrolytes, access, circuit function, anticoagulation, and medication clearance.
8. Reassess every day for kidney recovery and readiness to stop renal replacement therapy.

Clinical Synopsis & Reasoning

Acute kidney injury in critical illness ranges from transient creatinine elevation to complete loss of filtration with life-threatening electrolyte, acid-base, and volume complications. The decision to start renal replacement therapy should be based on the clinical consequences of kidney failure and the trajectory of the illness rather than on a single creatinine, BUN, or urine-output number. Definitive indications include refractory hyperkalemia, severe acidemia not correctable by other means, pulmonary edema or fluid overload compromising oxygenation, selected dialyzable intoxications, and uremic complications such as pericarditis, encephalopathy, or clinically important bleeding.

Once dialysis is required, modality is matched to physiology. Intermittent hemodialysis removes solute and fluid quickly over several hours. It is efficient for hemodynamically stable patients and for situations in which rapid clearance is desirable. Continuous renal replacement therapy removes solute and volume gradually over 24 hours and is often better tolerated in patients with vasopressor-dependent shock, severe fluid intolerance, or cerebral edema in whom abrupt osmotic and pressure shifts are undesirable. Prolonged intermittent therapies such as SLED occupy a middle ground and can be useful when staffing and hemodynamics permit.

No modality intrinsically cures AKI or reliably improves renal recovery simply by being continuous or intermittent. The important issues are timely initiation for true indications, avoidance of unnecessary dialysis when complications can be medically controlled, an appropriate delivered dose, anticoagulation and access management, and repeated evaluation for renal recovery.

Treatment Strategy & Disposition

Treat reversible causes of AKI first whenever possible. Restore effective perfusion without causing persistent fluid overload, stop or adjust nephrotoxic drugs, relieve urinary obstruction, treat sepsis, and correct severe metabolic abnormalities. Use temporizing therapy for hyperkalemia while arranging dialysis if potassium remains dangerous or continues to rebound. Treat pulmonary edema with diuretics when residual kidney function and hemodynamics allow, but do not delay renal replacement therapy when oxygenation remains compromised.

Choose CRRT for patients with marked hemodynamic instability, ongoing vasopressor escalation, major fluid-removal needs that cannot be tolerated intermittently, or significant intracranial pressure concerns. Choose intermittent hemodialysis when blood pressure is sufficiently stable and rapid solute or volume removal is desired. SLED can provide slower clearance than standard intermittent dialysis with less resource intensity than continuous therapy in some units. Modality may change over the course of the same illness as the patient stabilizes.

Prescribe ultrafiltration according to perfusion and cumulative fluid balance rather than an arbitrary goal. Monitor electrolytes, phosphate, magnesium, acid-base status, temperature, drug clearance, circuit clotting, and access complications. CRRT can substantially alter antimicrobial and anticonvulsant dosing. Reassess daily for spontaneous urine output, improving creatinine trajectory, and ability to maintain potassium, acid-base status, and volume without dialysis so therapy can be discontinued promptly when no longer needed.

Epidemiology / Risk Factors

• AKI is common in ICU patients with sepsis, shock, major surgery, trauma, and multi-organ failure.
• Only a subset of ICU AKI requires renal replacement therapy, but those who do have high illness severity.
• Fluid overload before or during dialysis is associated with worse respiratory and overall outcomes.
• Renal recovery may continue for weeks after critical illness, and some survivors leave hospital with persistent chronic kidney disease.

Investigations

Modality Selection

Pharmacology

Prognosis / Complications

• Need for dialysis in ICU AKI marks severe illness but does not necessarily imply permanent dialysis dependence.
• Recovery is less likely with preexisting advanced CKD, prolonged anuria, severe multi-organ failure, and major structural kidney injury.
• Hemodynamic instability and cumulative fluid overload increase complexity and mortality risk.
• Survivors require follow-up of creatinine, urine protein, blood pressure, medication dosing, and chronic kidney disease risk.

Patient Education / Counseling

• Explain that dialysis supports the body while the kidneys recover or while the underlying illness is treated.
• Clarify that CRRT is slower and continuous because the patient may not tolerate rapid fluid and solute shifts.
• Families should understand that a temporary dialysis catheter and anticoagulation can introduce bleeding, infection, and clotting risks.
• Discuss uncertainty about renal recovery honestly and arrange nephrology follow-up for survivors with persistent dysfunction.

Notes

The most common conceptual error is to equate a rising creatinine with a mandatory dialysis start. Creatinine is a marker of filtration, not a direct measure of the urgency of complications. A patient with severe refractory hyperkalemia and only moderate creatinine elevation may need immediate dialysis, while a patient with very high creatinine who is clinically stable and metabolically controlled may not require it at that moment.

Modality selection is similarly dynamic. CRRT may be the safest choice during vasopressor-dependent shock, followed by intermittent hemodialysis after recovery of cardiovascular stability. The clinical question should be which therapy best fits the patient today, not which modality is categorically superior.

References

1. KDIGO Clinical Practice Guideline for Acute Kidney Injury — Link
2. Surviving Sepsis Campaign International Guidelines 2026 — Link