Medically Reviewed and Compiled by Dr. Adam N. Khan, MD.
The main difference between Continuous Renal Replacement Therapy (CRRT) and standard Hemodialysis (HD) is speed and duration. Dialysis is a fast treatment, usually lasting 3 to 4 hours, designed to clean the blood quickly for stable patients.
CRRT is a slow, gentle, 24-hour-a-day process use
Medically Reviewed and Compiled by Dr. Adam N. Khan, MD.
The main difference between Continuous Renal Replacement Therapy (CRRT) and standard Hemodialysis (HD) is speed and duration. Dialysis is a fast treatment, usually lasting 3 to 4 hours, designed to clean the blood quickly for stable patients.
CRRT is a slow, gentle, 24-hour-a-day process used specifically for critically ill patients in the ICU whose hearts are too weak to handle the rapid fluid shifts of regular dialysis.
Think of dialysis like a high-speed car wash, while CRRT is like a steady, gentle rain that cleans the environment over a long period.
Understanding the Basics of Kidney Support
When kidneys fail, the body can no longer filter waste or manage fluid. This leads to a buildup of toxins that can be deadly. Doctors use “blood cleaning” machines to do the kidneys’ job. While both CRRT and Dialysis save lives, they are used in very different situations.
What is Hemodialysis?
Standard Hemodialysis is what most people think of when they hear “dialysis.” It is common for people with chronic kidney disease. It works by pumping blood out of the body, through a filter called a dialyzer, and back into the body. Because it happens fast, it can be hard on the heart.
What is CRRT?
CRRT stands for Continuous Renal Replacement Therapy. It is “continuous” because it never stops—it runs 24/7. It is found only in Intensive Care Units (ICUs). It mimics the natural kidneys much more closely by removing small amounts of waste and water every single minute of the day.
1. Speed and Fluid Balance
The biggest technical difference is how fast the machine works.
- Dialysis (The Sprint): During a 4-hour session, the machine might remove several liters of fluid. This is a lot of work for the heart. If a patient’s blood pressure is already low, dialysis could cause it to crash.
- CRRT (The Marathon): CRRT removes fluid in tiny drops over 24 hours. Because it is so slow, it doesn’t cause sudden drops in blood pressure. This makes it the only safe choice for patients in shock or with failing hearts.
2. Patient Stability and Location
Where the patient is located usually tells you which treatment they need.
| Feature | Standard Dialysis | CRRT |
| Location | Clinic or Hospital Ward | ICU (Intensive Care Unit) |
| Patient Status | Stable / Mobile | Critically Ill / Bedridden |
| Time Commitment | 3-4 hours, 3x per week | 24 hours a day, every day |
| Blood Pressure | Must be stable | Can be very low (unstable) |
3. How the Cleaning Process Works (Solute Clearance)
Both machines use a filter, but they use different physics to clean the blood.
Diffusion in Dialysis
Dialysis mostly uses diffusion. Imagine putting a tea bag in hot water. The tea moves from where there is “a lot of tea” to where there is “no tea.” In dialysis, waste moves from the high-concentration blood to the low-concentration cleaning fluid (dialysate).
Convection in CRRT
CRRT often uses convection (specifically in a mode called CVVH). This is like a pressure washer. The machine pushes blood against the filter with enough pressure to “drag” out large toxins along with the water.
This is better at removing the big “middle molecules” often found in patients with severe infections (sepsis).
4. Equipment and Specialized Care
Because CRRT is a 24/7 process, it requires a lot of resources.
- Nursing: A dialysis nurse might watch four patients at once in a clinic. A CRRT patient usually has a dedicated ICU nurse watching the machine every hour to ensure the blood doesn’t clot in the tubes.
- Anticoagulation: Since the blood is outside the body for a long time in CRRT, doctors must use blood thinners like citrate or heparin to keep the machine from clogging.
Frequently Asked Questions
Can you switch from CRRT to Dialysis?
Yes. This is the goal! Once a patient’s blood pressure stabilizes and they no longer need “pressors” (medicine to keep the heart beating), the doctor will “transition” them to intermittent dialysis.
Is CRRT painful?
No. The process itself is not painful. The patient usually has a large catheter (tube) in their neck or groin. Once that is in place, they don’t feel the blood moving. Most CRRT patients are sedated because they are very ill, but those who are awake generally find it comfortable.
Does CRRT mean the kidneys are gone forever?
Not necessarily. In the ICU, most patients have Acute Kidney Injury (AKI). This is often reversible. CRRT is a “crutch” used while the kidneys rest and heal.
Final Thoughts for Families
Seeing a loved one hooked up to a CRRT machine can be scary. The machine is large, has many humming parts, and is surrounded by bags of fluid. However, it is one of the most advanced ways we have to support life. It represents the “gentle” approach to medicine—doing slowly what the body can no longer do quickly.
If your loved one is on CRRT, it means the medical team is prioritizing stability. As the patient gets stronger, the goal will always be to move toward standard dialysis and, eventually, no dialysis at all.