Continuous Renal Replacement Therapy (CRRT) is a form of dialysis specifically designed for critically ill patients with acute kidney injury (AKI) who are hemodynamically unstable. Unlike conventional hemodialysis, which is performed over a few hours, CRRT works continuously over 24 hours or longer, providing a gentler and more controlled method of removing waste products, excess fluids, and correcting electrolyte and acid-base imbalances.
CRRT is most commonly used in intensive care units (ICUs) for patients with sepsis, multi-organ failure, or severe fluid overload. Its ability to provide stable hemodynamic control makes it an essential life-saving therapy in modern critical care.
The kidneys are vital organs responsible for filtering blood, eliminating waste products (such as urea and creatinine), regulating electrolytes, and maintaining fluid and acid-base balance. In acute kidney injury, these processes are impaired, leading to toxin accumulation, metabolic acidosis, and life-threatening electrolyte disturbances like hyperkalemia.
Standard intermittent hemodialysis (IHD) may cause rapid fluid and solute shifts, which can worsen instability in critically ill patients. CRRT was developed to mimic the natural kidney’s slow and continuous function, providing gradual clearance and fluid removal while minimizing sudden hemodynamic changes.
CRRT is indicated for patients with AKI or severe metabolic disturbances who are too unstable to tolerate intermittent hemodialysis. Common conditions leading to CRRT include:
Sepsis and septic shock – the leading cause of AKI in ICUs.
Multi-organ failure – where kidney dysfunction occurs alongside cardiac, hepatic, or respiratory failure.
Severe fluid overload – unmanageable with medications or intermittent dialysis.
Cardiac dysfunction – such as heart failure with pulmonary edema.
Rhabdomyolysis – muscle breakdown releasing toxins harmful to kidneys.
Severe electrolyte imbalances – like hyperkalemia or metabolic acidosis refractory to medical therapy.
Drug or toxin overdose – when removal of dialyzable substances is needed.
Patients requiring CRRT often present with signs of acute kidney dysfunction and systemic illness, including:
Decreased urine output (oliguria or anuria).
Swelling and edema due to fluid retention.
Shortness of breath from pulmonary edema.
Confusion, drowsiness, or seizures due to uremia or electrolyte imbalance.
Nausea, vomiting, and fatigue from toxin buildup.
Abnormal vital signs, particularly hypotension in septic or critically ill patients.
The decision to initiate CRRT is based on clinical findings and laboratory results. Diagnostic steps include:
History and examination – assessing fluid balance, mental status, and hemodynamic stability.
Blood tests – elevated serum creatinine, blood urea nitrogen (BUN), potassium, and abnormal acid-base balance.
Arterial blood gases (ABG) – identifying metabolic acidosis.
Urine output monitoring – oliguria or anuria confirms worsening kidney function.
Imaging – ultrasound of kidneys to rule out obstruction.
The diagnosis of AKI requiring CRRT is made when patients meet criteria for urgent renal replacement therapy and cannot tolerate conventional hemodialysis.
Management of AKI and kidney failure involves both conservative and replacement strategies:
Non-dialytic management
Intravenous fluids (when appropriate) to restore kidney perfusion.
Medications to correct electrolyte imbalances.
Diuretics to relieve fluid overload in select cases.
Discontinuing nephrotoxic drugs and treating underlying illness (such as infection).
Dialytic therapies
Intermittent Hemodialysis (IHD): Rapid clearance over 3–4 hours, but often poorly tolerated in unstable patients.
Sustained Low-Efficiency Dialysis (SLED): A prolonged but intermittent therapy lasting 6–12 hours.
Continuous Renal Replacement Therapy (CRRT): A continuous process, offering the gentlest clearance and best suited for unstable ICU patients.
CRRT can be delivered in different modalities, depending on whether solute removal is achieved by diffusion, convection, or both. Common modes include:
Continuous Venovenous Hemofiltration (CVVH): Removes solutes mainly by convection (filtration).
Continuous Venovenous Hemodialysis (CVVHD): Removes solutes by diffusion across a dialyzer membrane.
Continuous Venovenous Hemodiafiltration (CVVHDF): Combines convection and diffusion for maximum clearance.
Vascular access – A double-lumen central venous catheter is inserted (usually in the internal jugular, femoral, or subclavian vein).
Connection to CRRT machine – Blood is continuously pumped through a filter (hemofilter).
Blood flow – Typically slower than conventional hemodialysis (100–200 mL/min).
Fluid management – Controlled removal of excess fluids over 24 hours.
Anticoagulation – Regional citrate or heparin may be used to prevent clotting of the circuit.
Continuous monitoring – Vital signs, fluid balance, and laboratory parameters are closely tracked.
Although CRRT is not a surgical procedure, patients require close monitoring during and after therapy:
Hemodynamic monitoring – ensuring blood pressure and heart function remain stable.
Electrolyte balance – adjusting replacement fluids to maintain potassium, calcium, and bicarbonate levels.
Nutrition – specialized feeding plans to meet caloric and protein needs without fluid overload.
Fluid management – recording intake and output meticulously.
Infection prevention – strict catheter care to avoid bloodstream infections.
Once the patient stabilizes, CRRT may be transitioned to intermittent hemodialysis or discontinued if kidney function recovers.
While CRRT is considered safe and effective, potential complications include:
Hypotension – though less common than with IHD, may occur if fluid is removed too aggressively.
Electrolyte and acid-base imbalances – if replacement solutions are not properly adjusted.
Hypothermia – due to extracorporeal blood circulation.
Bleeding – related to anticoagulation use.
Catheter-related complications – such as clotting, infection, or thrombosis.
Filter clotting – leading to interruptions in therapy.
The outcome of patients receiving CRRT depends more on the underlying illness than on the dialysis itself. CRRT often acts as a supportive therapy while the body fights sepsis, recovers from surgery, or stabilizes from shock.
Short-term: CRRT effectively manages fluid balance and metabolic derangements in unstable patients.
Long-term: Some patients regain full kidney function, while others may require prolonged dialysis or progress to chronic kidney disease (CKD).
Patients or caregivers should seek urgent medical attention if there are signs of:
Markedly reduced urine output.
Rapidly worsening swelling or shortness of breath.
Severe electrolyte imbalance symptoms (chest pain, palpitations, seizures).
Signs of infection around dialysis catheter (redness, pain, fever).
Persistent confusion, drowsiness, or loss of consciousness.
Early evaluation improves survival and prevents life-threatening complications.
Continuous Renal Replacement Therapy (CRRT) has revolutionized the management of critically ill patients with acute kidney injury and fluid-electrolyte disturbances. By providing continuous, gentle clearance, CRRT is safer for unstable patients compared to conventional dialysis.
While not without risks, CRRT offers crucial support, buying time for organ recovery and improving outcomes in life-threatening conditions. Patients and families should understand that CRRT is part of an intensive care strategy and that treatment decisions must always be made in consultation with healthcare professionals.
Caring for every kidney, with expertise and compassion.
Trusted Nephrologist Doctor in Hyderabad.
