Continuous Renal Replacement Therapy, or CRRT, is a continuous form of blood purification designed for critically ill patients. This therapy is performed exclusively in an Intensive Care Unit (ICU) setting, where it functions as an artificial kidney system for individuals whose own kidneys have suddenly failed. Unlike traditional dialysis that occurs in sessions, CRRT operates 24 hours a day to gently and slowly remove waste products and excess fluid from the body.
This process provides a constant and stable internal environment, giving the patient’s body and kidneys time to rest and recover. The therapy is a temporary measure intended to support the patient until their kidney function improves or they become stable enough for other forms of dialysis.
Purpose of Continuous Renal Replacement Therapy
The primary reason for using CRRT is to manage severe Acute Kidney Injury (AKI), a condition where the kidneys abruptly lose their ability to filter waste from the blood. This sudden failure leads to the accumulation of toxins, electrolytes, and fluid. CRRT is specifically indicated for patients who are hemodynamically unstable, meaning they have very low or erratic blood pressure and cannot withstand the rapid fluid shifts that occur with conventional dialysis.
These critically ill individuals often require large volumes of intravenous fluids, medications, and nutrition, which can lead to dangerous fluid overload when the kidneys are not working. CRRT gently removes this excess fluid, helping to stabilize blood pressure and reduce strain on the heart and lungs. The therapy also meticulously corrects dangerous imbalances in blood chemistry, such as high levels of potassium or acid, which can cause fatal heart rhythm disturbances if left untreated.
The CRRT Process
The procedure begins with the placement of a central venous catheter, often called a dialysis catheter. A physician inserts this large, flexible tube into a major vein in the neck or groin using sterile techniques to minimize infection risk. This catheter has two separate channels: one to draw blood out of the body and another to return the purified blood.
Once access is secured, the catheter is connected to the CRRT machine at the patient’s bedside. A pump on the machine gently draws blood at a controlled rate and directs it into a specialized filter known as a hemofilter. This filter acts as an artificial kidney, containing a semipermeable membrane that allows waste products, excess electrolytes, and water to be removed from the blood.
As the blood passes through the hemofilter, a specially prepared solution, known as replacement fluid or dialysate, may be added to the blood to help correct electrolyte imbalances. The cleaned blood is then warmed to body temperature and returned to the patient through the second channel of the catheter. This entire circuit runs continuously under the constant supervision of specially trained ICU nurses.
Comparison with Intermittent Hemodialysis
While both CRRT and Intermittent Hemodialysis (IHD) purify the blood, they are designed for very different patient situations. The most significant difference is the duration and rate of filtration. CRRT is a slow and continuous process that runs 24 hours a day, while IHD is a much faster therapy, completing its work in sessions that typically last three to four hours, several times a week.
This difference in speed dictates the type of patient each therapy can support. CRRT is reserved for critically ill, hemodynamically unstable patients in the ICU, as its gentle nature prevents the sudden drops in blood pressure that can occur with rapid fluid removal. IHD is better suited for patients who are more stable, including those with chronic kidney failure who receive treatment at outpatient dialysis centers.
The location of treatment also differs. CRRT is exclusively an ICU-based therapy, requiring constant monitoring by a specialized critical care team. IHD, however, is more versatile and can be administered in various settings, including hospitals, outpatient clinics, and even at home for some patients.
Potential Complications
Although CRRT is a life-sustaining therapy, it is not without risks, which is why patients undergo intensive monitoring. The most common complications include:
- Hypotension: Low blood pressure can occur as the circulation of blood outside the body and the removal of fluid can cause blood pressure to drop, especially when treatment is initiated.
- Circuit Clotting: To prevent this, an anticoagulant medication is administered, but clots can still form in the hemofilter and blood circuit, obstructing blood flow and stopping the therapy. When this happens, the nurse must replace the entire circuit, which can lead to small amounts of blood loss.
- Infection: The central venous catheter is a potential source of complications, as it provides an entry point for bacteria into the bloodstream. This requires strict sterile protocols during insertion and maintenance.
- Electrolyte Imbalances: The continuous nature of the therapy demands meticulous management of the patient’s blood chemistry. Imbalances in electrolytes like potassium, calcium, and phosphate can occur if the replacement fluids are not adjusted precisely to the patient’s needs.
The Healthcare Team and Monitoring
The delivery of CRRT requires a dedicated interprofessional team. This team is led by a critical care physician, or intensivist, and a kidney specialist, known as a nephrologist. Together, they prescribe the specific parameters of the therapy and make adjustments based on the patient’s response.
At the bedside, highly trained ICU nurses are responsible for the hour-to-hour management of the CRRT machine. They continuously monitor the patient’s vital signs, check the pressures and flows on the machine, and troubleshoot any alarms. Their duties also include changing the bags of sterile fluids and ensuring the vascular access site remains clean.
This constant oversight is supplemented by frequent laboratory tests, with blood samples drawn regularly to monitor the effectiveness of the therapy. Pharmacists and dietitians also play important roles, helping to adjust medication dosages and nutritional support to account for the continuous filtration process.