Overview of Continuous Renal Replacement Therapy
There are several different treatments available for managing a severe case of acute kidney injury (AKI), which is a sudden episode of kidney failure or damage. These treatments are called renal replacement therapies (RRTs) and they include methods like intermittent hemodialysis (IHD), continuous renal replacement therapy (CRRT), and prolonged intermittent RRT. The choice of treatment method depends on why the patient needs dialysis, the doctor’s preference, current research data on outcomes, and most importantly, the patient’s blood flow stability.
In a 2015 study of patients with AKI in intensive care units (ICUs), it was found that CRRT was the chosen treatment in 75.2% of sessions, compared to 24.1% using intermittent dialysis, and 0.7% using peritoneal dialysis, which is a type where the lining of the belly (peritoneum) filters the blood.
CRRT involves slowly purifying the blood and balancing its fluid over a 24-hour period. This is done by filtering the blood through a semi-permeable membrane that lets certain things pass through it by using different solute transport mechanisms. Depending on the specific method used for filtering, there are three types of CRRT. These are continuous venovenous hemofiltration (CVVH), continuous venovenous hemodialysis (CVVHD), and continuous venovenous hemodiafiltration (CVVHDF), all of which are modes that filter the blood and remove waste products.
Anatomy and Physiology of Continuous Renal Replacement Therapy
If you need to undergo a medical procedure called Continuous Renal Replacement Therapy (CRRT), your doctor will have to gain access to your bloodstream using a special tube known as a dual-lumen catheter. It’s put into a large vein, such as the one in your neck (called the internal jugular vein) or the one in your leg (called the femoral vein). This catheter can be put in temporarily if the treatment is short-term, but longer treatments will require a permanent (or tunneled) catheter.
The ideal place to put this catheter is in the right neck vein, as it allows the best possible blood flow. Sometimes, due to specific circumstances such as an individual’s weight or vein obstructions, the catheter might be placed into the left neck vein or femoral vein. However, these alternatives can impact blood flow. The subclavian vein, located under your collar bone, isn’t recommended because its use could cause future problems for blood vessel access.
The length of catheter you’ll need depends on your height and which part of your body the catheter is inserted. The placement can be done bedside using aseptic techniques and guidance from an ultrasound, following the Kidney Disease Improving Global Outcomes (KDIGO) guidelines. The catheter’s position is usually confirmed through chest x-rays and if the catheter isn’t positioned correctly, it could lead to possible blood flow issues and clotting.
The goal of CRRT is to mimic how your kidneys work and clear waste from your blood. This is done using two main methods. One is diffusion, which is mainly used for smaller particles, and the other is convection, which is used for mid-sized particles. In this treatment, blood flow and the flow of dialysate (a solution to clean your blood) are carefully regulated, allowing small particles in your blood to balance out with the solution. This balance helps efficiently remove waste from your blood.
The CRRT procedure can be fine-tuned to cater to your specific needs. For instance, if you need to remove excess fluid from your body, a therapy called Continuous Venovenous Hemofiltration (CVVH) can be used. This involves removing, treating, and replacing some of your blood fluid, while also removing some additional fluid as necessary. On the other hand, Continuous Venovenous Hemodialysis (CVVHD) involves using the dialysate to remove waste and excess fluid. Yet another variation, Continuous Venovenous Hemodiafiltration (CVVHDF) utilizes a combination of both techniques.
The effectiveness of CRRT in cleaning your blood is measured through the general clearance equation. This measures how successfully the therapy removes waste from your blood based on the amount of cleaned fluid and the gradient or slope of the concentration of wastes in your blood. This calculation helps medical professionals to decide the best way to adjust the therapy for optimum results.
In summary, CRRT uses sophisticated techniques to clean your blood when your kidneys can’t do it alone. Your doctor will plan the best way to administer this therapy, taking into consideration a number of factors to ensure that you get the best possible care.
Why do People Need Continuous Renal Replacement Therapy
If a patient is experiencing severe kidney problems, such as the kidneys not removing enough fluid or too many electrolytes building up in the body, they might need a treatment called renal replacement therapy (RRT). This is a way to do what the kidneys normally do and remove harmful substances from your blood. The specific type of RRT a person receives depends on the individual’s medical condition.
Continuous Renal Replacement Therapy (CRRT), for instance, is often used when there’s a noticeable drop in the flow of blood due to severe health instability. CRRT aids in adjusting fluid levels and enables more precise fluid removal than intermittent hemodialysis (IHD). This makes it especially useful for patients with high metabolic activities or rapidly breaking down cells, such as in tumor lysis syndrome or rhabdomyolysis.
Another advantage of CRRT is that it gradually removes substances that attract water (osmotically active substances) from the body. This can prevent a sudden increase in pressure inside the skull (intracranial pressure), which can potentially cause brain damage, making it an ideal choice for patients experiencing swelling in the brain.
IHD, on the other hand, is more impactful when there’s urgent need to remove toxins and excess potassium especially in life-threatening situations. A good example is when there’s too much potassium in the blood, a condition known as hyperkalemia. IHD is also beneficial in rapidly removing specific toxins that do not attach well to proteins and spread across a large volume in the body. In situations like these, the healthcare team may use IHD first for immediate removal, then follow-up with CRRT to manage any redistribution of toxins from the cells back into the bloodstream. Clinical reasons for this combination removal process can include exposure to an overdose of certain medication like metformin.
Lastly, in situations of extreme acid build-up (metabolic acidosis) or severe imbalance in the body’s salts (electrolytes), IHD usually serves the purpose. However, in cases where the patient’s health is shaky, CRRT can also play a role in managing these conditions.
Another group of patients who often need RRT are those on a life-support technique called extracorporeal membrane oxygenation (ECMO). This technique frovide oxygen to a patient when their heart and lungs are not functioning properly. These patients often end up with acute kidney injury (AKI) due to changes in blood flow. ECMO can cause fluid overload and electrolyte imbalances, hence necessitating the need for RRTs like CRRT. It’s important to note that managing such patients requires extensive knowledge of the procedure to prevent potential complications.
When a Person Should Avoid Continuous Renal Replacement Therapy
There are times when Continuous Renal Replacement Therapy (CRRT) – a treatment for kidney failure where the blood is cleaned out little by little over a longer period – might not be suitable. This might be because the patient’s health situation requires a quicker treatment. Certain circumstances might also make CRRT a less favorable choice.
For example, if a patient has decided they do not want dialysis – a treatment that clears waste and excess fluids from the blood when the kidneys are not able to – then CRRT would not be an option.
If the patient has problems with their blood vessels that might make the access for CRRT difficult, or if the hospital or clinic doesn’t have trained staff or the necessary equipment, CRRT might not be possible.
Furthermore, if a patient is going through irreversible liver failure and they are not a suitable candidate for a liver transplant, CRRT may not help their condition.
Equipment used for Continuous Renal Replacement Therapy
Continuous Renal Replacement Therapy, or CRRT, is a treatment method for helping kidneys perform their tasks when they aren’t doing well. It uses a specialized machine, designed specially for this use. To run this machine, you need:
* Blood purification machine (which works to clean the blood)
* Blood warmer (a device to keep the blood at the right temperature)
* Filter (used in the purification process)
* Dialysate (a fluid that helps remove waste substances from the blood)
* Replacement fluid (a special fluid that replaces the body’s own fluids that are lost during this process)
When we use dialysis and replacement solutions, these can be based on either lactate or bicarbonate. There are different types of these available in pre-mixed bags from companies like Baxter, NxStage, and B.Braun. If you have liver failure or problems with your blood flow, it might be better to use bicarbonate-based solutions, because lactate-based ones could cause lactic acidosis (an excessively high level of lactate in the body).
The tubing and the dialysis membrane that the blood comes into contact with during CRRT can cause the platelets in the blood to become active and release pro-inflammatory markers which can lead to clotting in the filter. This reduces how well the dialysis works as less surface area is available for it to interact with the blood. To prevent this, anticoagulation (stoppage of blood clotting) is needed.
Unfractionated heparin is mostly used to prevent clotting, even though it could lead to heparin resistance, a decrease in the number of platelets, and bleeding. There are other versions of heparin which are less likely to cause these issues but can be more expensive than the typical heparin.
Some facilities follow KDIGO guidelines and choose to use citrates as the anticoagulation agent instead of heparin, as citrates pose less of a clotting risk and less bleeding risk compared to systemic heparin. Citrate works by binding with calcium in the blood, impacting the calcium-based clotting factors and blocking clot production. To inhibit clotting entirely, target citrate and calcium levels need to be 3 to 5 mmol/L and less than 0.35 mmol/L, respectively. Keep in mind, there are pros and cons to using both systemic and regional anticoagulation. It depends on an individual’s condition and how the CRRT machine interacts with the body.
Who is needed to perform Continuous Renal Replacement Therapy?
Doing a CRRT (Continuous Renal Replacement Therapy), which is a kind of dialysis for seriously ill patients, involves teamwork throughout the whole process. A nephrology specialist (a doctor who specializes in kidney diseases and conditions) and a team of CRRT nurses work together to prioritize tasks, ensure the process is high quality and follow standard procedures.
Getting extra specialists to help with patients in the intensive care unit (ICU), which treats seriously ill patients, is not a new concept. The specialists we typically bring in to help manage patients on CRRT, outside of the regular ICU staff, are:
- Respiratory care practitioners (help patients with their breathing)
- Nutritional support team (ensure patients are eating right and not malnourished)
- Clinical pharmacologists (manage medicine)
- Diagnostic and interventional radiologists (use imaging techniques for diagnosis and treatment like X-rays, CT scans)
- Cardiologists (heart doctors)
- Rehabilitation and physiotherapy specialists (help patients recover physical skills)
- ICU-trained nursing staff
All of these healthcare professionals bring different skills and make patient care whole. They work together with the ICU team so that the patient gets the best possible result from the treatment.
Preparing for Continuous Renal Replacement Therapy
Patients with acute kidney injury (AKI) often need continuous renal replacement therapy (CRRT), a type of treatment used when the kidneys aren’t working properly. It-filter and clean the blood when the kidneys can’t. A recommended amount of effluent, which is the fluid removed from the body during treatment, is between 20 to 25 mL/kg/hr. This recommendation is based on studies conducted by the Veterans Affairs and the National Institutes of Health. Giving more than this amount hasn’t shown any additional benefits. However, many factors can affect the actual amount administered, like any machine downtime because of procedures, tests, or the need to replace parts like the filter or fluid bag.
There is no one-size-fits-all approach when it comes to fluid removal during CRRT. Doctors adjust the amount based on the patient’s condition, so this can vary from patient to patient. However, it’s generally recommended to limit the fluid removal rate to less than 1.5 to 2.0ml/kg/hr.
Another important aspect is the blood flow rate during CRRT. To make sure that the blood is being cleared out of waste as efficiently as possible without affecting the patient’s blood pressure, doctors recommend keeping a minimum blood flow rate of 150 mL/min. This balance ensures a stable blood flow while the treatment is being done.
How is Continuous Renal Replacement Therapy performed
Continuous Venovenous Hemofiltration or CVVH, is a method often used to clean or filter the blood of patients who have kidney problems. Here’s how it works: The patient is connected to a machine that uses pressure to push the patient’s blood through a filter. The filter cleans out a large amount of waste from the blood. However, along with waste, some important fluids are also removed. To solve this, some medical fluid, also known as substitute or replacement fluid, needs to be added back into the blood to replace what was removed.
There is a bit of a balancing act here though, because if too much fluid is removed and not adequately replaced, the blood can thicken (a condition known as hemoconcentration). This can cause issues like clotting and blockages. Therefore, doctors try to limit the amount of fluid that is filtered out to no more than 20% to 25% of the total blood volume. Additionally, placement of the replacement fluid is important. Adding it before filtration can lower the risk of clotting but also reduces the amount of waste that is removed.
CVVHD or Continuous Venovenous Hemodiafiltration is another method where waste is removed from the blood by a different mechanism called diffusion, working sort of like how a tea bag steeps in hot water. The waste in the blood moves from an area of high concentration (the blood) to an area of low concentration (dialysate – a special fluid designed to draw waste out of the blood).
CVVHDF is a combination method that uses both filtering and diffusion to remove waste from the blood. This approach can be particularly useful for managing issues with electrolytes (salts in the body that help regulate heart and nerve function) and in case of lactic acidosis (a buildup of lactic acid in the body). In this case, a bicarbonate buffer can be used in the process to counterbalance the acid in the body.
One thing to keep in mind is that calcium is often not included in the replacement fluids, so patients usually need additional calcium to replace what is lost in the process.
If problems arise while using the CVVH machine, the machine can give alerts or “alarms.” For example, alarms may go off if there is a problem with blood flow, like a kink or clot in the line, or if the patient’s blood pressure drops too low. If air ends up in the line, the filtering process has to be stopped and the problem has to be fixed before it can be restarted. Also, the machine has to be monitored closely to make sure the input and output of fluids are balanced. If there’s too much or too little fluid, the bags might need to be adjusted to correct the problem.
In a nutshell, CVVH, CVVHD, and CVVHDF are techniques used to filter and clean the blood, removing waste and maintaining body chemistry balance, especially for patients with kidney issues who can’t do it themselves. The doctors and care team will choose the best method for the patient based on the individual’s specific condition and needs.
Possible Complications of Continuous Renal Replacement Therapy
Just like any other medical procedure, Continuous Renal Replacement Therapy (CRRT), a type of kidney dialysis, comes with certain risks. These should be discussed with the patient or their family when planning treatment.
The first set of risks are tied to the process of inserting lines into blood vessels. This can sometimes result in bleeding, the creation of an abnormal connection between an artery and a vein (arteriovenous fistula), infection, and blood clots.
The therapy itself can also lead to abnormalities in the levels of certain substances in your blood (electrolytes), potential loss or reduction of trace elements or antibiotics in your body, low body temperature (hypothermia), and low blood pressure (hypotension). While low blood pressure is less common with CRRT than in other types of dialysis, it can still occur if too much fluid is removed too quickly from the body.
To keep an eye on these possible complications, doctors will frequently monitor your electrolyte levels and overall blood condition especially in the first 24 to 48 hours of starting CRRT. If you’re stable, the checks may become less frequent after the initial period. If a substance called citrate is used to prevent blood clotting during the procedure, your calcium levels will need to be checked more regularly.
It’s common for patients undergoing CRRT to experience low calcium, potassium, and phosphate levels in their blood. The extent of these deficiencies can often depend on how intense the dialysis therapy is. Solutions to address this can include supplements, special feeds, or using a dialysis fluid containing phosphate.
Another consideration with CRRT is the potential loss of medications from the body. Some drugs, particularly water-soluble antibiotics, may be removed from the body during the procedure. This requires careful management, especially in patients with serious infections who need appropriate doses of antibiotics.
Finally, the therapy may also result in losses of essential substances such as amino acids, micronutrients, and certain vitamins. For this reason, a careful balance of dietary intake and supplements may be recommended. There are also risks involved with using an out-of-body (extracorporeal) circuit, like allergic reactions, the possibility of air bubbles entering the blood (air embolization), or blood loss during the replaceable parts of the equipment.
What Else Should I Know About Continuous Renal Replacement Therapy?
Continuous Renal Replacement Therapy (CRRT) is a type of treatment used on people whose kidneys are not working properly. A lot of things need to be considered before starting CRRT. Primarily, the seriousness of the illness and the need for the procedure are evaluated. Your doctor determines the severity of the kidney injury by looking at how it’s progressing. Other factors are the balance of salts, acid, and base in your blood, signs of too much fluid in the body, and how well your other organs are functioning. The right time to begin CRRT is still being debated by doctors.
Starting CRRT early could help correct imbalance of salts in your blood and excessive amounts of a waste product called urea in the blood (azotemia) before they become serious problems, but the treatment also has potential complications. Predicting how kidney injury will progress can be hard, so it’s not always easy to identify patients whose kidney damage is likely to last for a long time. Factors such as recovery potential of the kidney injury, limited urine output, and the nature of the factor causing the kidney injury can be used to evaluate the situation. Consequently, the decision on when to begin CRRT can be different for each patient.
Deciding when to start treatment in serious cases of kidney injury is a difficult decision because kidney function can change unexpectedly. A study found that a test using a drug called furosemide helped identify patients with severe kidney injury who were more likely to need CRRT. In the study, 78% of patients who didn’t respond to a dose of furosemide, meaning they produced less than 200 mL of urine in 2 hours, later needed to start CRRT. Although this method didn’t affect survival rates, more research is needed to confirm these findings.
There is no universal rule on when to stop CRRT or switch to another treatment called Intermittent Hemodialysis (IHD). However, a 2021 study suggested that checking for urine output, blood levels of certain chemicals (like creatinine, potassium, bicarbonate), pH level (which measures acidity), urinary urea, and urinary creatinine can help determine when a patient can stop receiving CRRT. Chronic kidney disease, how long patients have been on CRRT, and the amount of urine a patient produces when the treatment is stopped may also predict whether treatment can be stopped successfully. Following treatment, patients will continue to be evaluated to see if their kidney function is improving.
