Haemofiltration – Diagnostics – Overview of Information and Clinical Research

Hemofiltration is a specialized medical treatment used to support patients whose kidneys are not working properly, particularly those in intensive care units. This therapy helps remove excess water and waste products from the blood when the body cannot do so on its own, offering a gentler alternative to traditional dialysis for critically ill patients.

Introduction: Who Needs Hemofiltration

Hemofiltration is primarily used for people who develop acute kidney injury, which means the kidneys suddenly stop working as they should. This condition is particularly common among patients who are critically ill and admitted to intensive care units. Research shows that around 40% of patients in intensive care develop some form of kidney injury, and between 17% and 24% of these patients will need some type of kidney support treatment during their stay^[6].

Not everyone with kidney problems receives hemofiltration. Doctors typically recommend this treatment for patients whose kidneys have failed to the point where waste products and excess fluid are building up dangerously in the body. The treatment becomes necessary when the kidneys can barely function at all, and other medical approaches have not been successful^[2]. In particular, hemofiltration is often chosen for patients who are hemodynamically unstable, meaning their blood pressure is low or fluctuating, because this treatment is gentler on the body than traditional dialysis methods^[2].

People who should seek medical evaluation for possible kidney support therapy include those experiencing severe fluid overload that does not respond to medications, dangerous changes in blood chemistry such as extremely high potassium levels, severe metabolic acidosis (when the blood becomes too acidic), or the buildup of toxic substances that the kidneys normally remove^[3]. Additionally, hemofiltration may be considered for patients with certain poisonings or drug overdoses, as it can help remove these substances from the bloodstream^[3].

⚠️ Important

Hemofiltration is almost always used as a treatment rather than a diagnostic tool itself. The decision to start hemofiltration is based on clinical signs and laboratory test results that show the kidneys are not working adequately. This treatment is typically reserved for patients in intensive care settings where close monitoring is available around the clock.

Diagnostic Methods for Kidney Function

Before hemofiltration can be started, doctors must first diagnose the extent of kidney dysfunction and determine whether this treatment is necessary. This diagnostic process involves several types of tests and assessments that work together to paint a complete picture of how well the kidneys are functioning.

Blood Tests

Blood tests are the cornerstone of diagnosing kidney failure. When kidneys fail, certain waste products that are normally filtered out begin to accumulate in the bloodstream. Doctors measure substances called urea and creatinine, which are waste products that healthy kidneys remove. When levels of these substances rise significantly in the blood, it indicates the kidneys are not doing their job^[4].

Blood tests also measure electrolytes, which are minerals in the blood that help regulate many body functions. Failing kidneys cannot properly balance electrolytes, leading to dangerous levels of potassium, sodium, calcium, and other minerals. High potassium levels, in particular, can cause life-threatening heart rhythm problems, making this a critical measurement^[9]. Additionally, doctors check blood pH levels to see if the blood has become too acidic, a condition called metabolic acidosis that occurs when kidneys cannot remove enough acid from the body.

Urine Tests

Examining the urine provides valuable information about kidney function. Doctors look at how much urine a patient is producing, as very low urine output often signals severe kidney problems. They also test the urine for the presence of protein or blood, which should not normally be present in significant amounts^[4].

The concentration of the urine is also important. Healthy kidneys can concentrate urine when the body needs to conserve water. When kidneys are failing, the urine may become very dilute because the kidneys have lost this ability to concentrate waste products effectively.

Assessment of Fluid Balance

Doctors carefully monitor how much fluid a patient is taking in versus how much they are putting out through urine and other routes. When kidneys fail, fluid can accumulate in the body, leading to swelling in the legs, lungs, or other areas. This fluid overload can be life-threatening if it affects the lungs or heart. Physical examination and daily weight measurements help doctors assess whether fluid is building up in dangerous amounts^[15].

Clinical Signs and Symptoms

Beyond laboratory tests, doctors evaluate the overall clinical condition of the patient. They look for signs that kidney failure is affecting other organs, such as confusion or altered mental status from the buildup of toxins, difficulty breathing from fluid in the lungs, or signs of heart strain. The patient’s blood pressure stability is also crucial, as hemodynamically unstable patients (those with low or fluctuating blood pressure) are more likely to benefit from hemofiltration rather than traditional dialysis^[2].

Distinguishing from Other Conditions

An important part of diagnosis involves determining whether kidney failure is acute (sudden) or chronic (long-term), and whether it is reversible. Doctors use imaging tests such as ultrasound to look at the size and structure of the kidneys. Chronic kidney disease often causes the kidneys to shrink and develop scarring, while in acute kidney injury, the kidneys may appear normal in size^[2].

Doctors also need to identify the underlying cause of kidney failure. This might involve additional tests to check for infections, autoimmune diseases, obstruction of the urinary tract, or damage from medications or toxins. Understanding the cause helps guide treatment decisions and determines whether the kidney failure is likely to be temporary or permanent.

Qualification Criteria for Hemofiltration Treatment

While hemofiltration is not typically used in clinical trials in the same way experimental medications are, there are standard medical criteria that doctors use to determine whether a patient is suitable for this treatment. These criteria are based on established medical practice and guidelines rather than research trial protocols.

Severity of Kidney Dysfunction

The primary criterion for starting hemofiltration is the severity of kidney failure. Doctors typically consider hemofiltration when kidney function has dropped to very low levels, generally when the glomerular filtration rate (GFR), which measures how well kidneys filter blood, falls below 10-15 milliliters per minute^[4]. At this level, the kidneys are performing less than 15% of their normal function, and the body cannot adequately remove waste products or maintain proper fluid and electrolyte balance.

Hemodynamic Status

A key factor in selecting hemofiltration over traditional hemodialysis is the patient’s blood pressure stability. Hemofiltration is preferred for patients who are hemodynamically unstable because it removes fluid and waste products more slowly and gently than traditional dialysis. This slow, continuous approach causes less dramatic shifts in blood pressure and fluid balance, making it safer for critically ill patients whose bodies cannot tolerate rapid changes^[2]^[6].

Vascular Access

Before hemofiltration can begin, patients need what is called vascular access, which means a way to connect their blood vessels to the hemofiltration machine. This typically involves placing a large catheter (tube) into a major vein, usually in the neck, chest, or groin. The catheter must be large enough to allow blood to flow out to the machine and return to the body at adequate rates^[2]^[8].

The size and type of catheter needed depends on the patient’s size and weight. For small patients, including children, specialized smaller catheters are used. For adult patients, larger catheters are placed to achieve the necessary blood flow rates. Doctors must ensure the catheter is functioning properly before hemofiltration can start^[15].

Treatment Location and Monitoring Capability

Hemofiltration requires intensive monitoring and is almost always performed in an intensive care unit setting. Patients receiving this treatment need continuous supervision by specially trained nurses and doctors. The treatment runs 24 hours a day, unlike traditional dialysis which typically runs for a few hours at a time^[6]. This means the hospital must have the appropriate equipment, trained staff, and intensive care beds available.

Absence of Contraindications

Certain conditions may make hemofiltration inappropriate or require special modifications. Patients with severe, uncontrolled bleeding may not be suitable candidates because hemofiltration typically requires anticoagulation (blood-thinning medication) to prevent clotting in the filter. However, specialized techniques using regional citrate anticoagulation can sometimes be used in patients at high risk for bleeding^[1]^[14].

Patients must also be evaluated for their ability to tolerate the procedure physically. Very small patients, particularly newborns and young infants, require specialized equipment and expertise. The medical team must assess whether the benefits of hemofiltration outweigh the risks for each individual patient^[15].

⚠️ Important

The decision to start hemofiltration is not made based on a single test result but rather on the complete clinical picture. Doctors consider the trend of kidney function tests over time, the patient’s overall condition, the presence of life-threatening complications from kidney failure, and whether the kidney injury is likely to improve with supportive care alone. Regular monitoring throughout treatment includes checking electrolyte levels every 4 hours initially, and blood chemistry tests multiple times daily to ensure the treatment is working safely and effectively^[9]^[15].

Prognosis and Survival Rate

Prognosis

The outlook for patients receiving hemofiltration depends largely on the underlying cause of kidney failure and the patient’s overall health status. For patients with acute kidney injury in the intensive care unit, the prognosis varies considerably. Some patients will recover kidney function and no longer need any form of dialysis or hemofiltration, while others may remain dependent on some form of kidney support therapy. Research comparing hemofiltration to traditional hemodialysis has not found significant differences in mortality rates or in the likelihood that patients will recover kidney function^[1].

Several factors influence whether a patient’s kidneys will recover. If the acute kidney injury was caused by a reversible condition, such as severe dehydration, infection, or temporary reduction in blood flow to the kidneys, there is a good chance that kidney function will return once the underlying problem is treated. However, if the kidney damage was severe or resulted from a chronic progressive disease, recovery is less likely^[1].

The presence of other failing organs significantly affects prognosis. Patients with multiple organ dysfunction syndrome, where several body systems are failing simultaneously, face more serious outcomes. The more organs that are affected, the lower the chance of survival and recovery. Additionally, patients who were hemodynamically unstable or in shock before starting hemofiltration tend to have poorer outcomes than those who were more stable^[6].

Survival Rate

Survival rates for patients receiving kidney replacement therapy in intensive care units remain challenging. For patients on dialysis generally, including those receiving hemofiltration, reported annual mortality rates range from approximately 13% in Australia and about 15% in New Zealand, to nearly 18% in Europe, and as high as 25% in the United States^[13]. However, these figures represent all dialysis patients and include those with chronic kidney disease, not just those receiving hemofiltration for acute kidney injury in intensive care settings.

It is important to understand that these mortality statistics reflect the serious nature of the conditions that require intensive care and kidney support, rather than the effectiveness of hemofiltration itself. Many patients who need hemofiltration are critically ill with multiple health problems, which significantly impacts their survival chances regardless of the kidney support method used.

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