Aquapheresis is a medical procedure that removes excess salt and water directly from your blood using a special filter. It’s primarily used for patients with heart failure whose bodies retain dangerous amounts of fluid, especially when standard water pills (diuretics) aren’t working well enough. The procedure works outside the body: blood is drawn out through a catheter, passed through a filter that separates out the extra fluid, and then returned to the patient.
How the Procedure Works
During aquapheresis, a catheter draws blood from a vein and sends it through a device containing a semipermeable membrane, sometimes called a hemofilter. Pressure across that membrane pushes plasma water (the fluid portion of blood carrying excess salt) through the filter while keeping blood cells and proteins on the other side. The filtered blood returns to your body through the same or a second catheter, and the removed fluid collects in a disposal bag.
What makes this different from diuretics is the composition of the fluid removed. Diuretics cause your kidneys to excrete water, but the urine they produce is relatively low in sodium. The fluid pulled out by aquapheresis is nearly identical to your blood’s salt concentration, roughly 134 to 138 millimoles of sodium per liter. That means for every liter of fluid removed, aquapheresis takes significantly more sodium with it than diuretics do. Since sodium is what drives fluid retention in heart failure, this distinction matters.
Another advantage is that aquapheresis removes fluid without directly triggering the hormone systems that cause your body to hold onto even more salt and water. Diuretics can activate what’s known as the renin-angiotensin-aldosterone system, a feedback loop that works against the goal of reducing fluid. Aquapheresis avoids this, as long as fluid is removed at a rate the body can keep up with.
What the Treatment Feels Like
The FDA-cleared Aquadex FlexFlow system, the primary device used in the U.S., can remove up to 500 milliliters of fluid per hour, though the actual rate is adjusted based on how you’re responding. In practice, rates vary widely. In one major trial (AVOID-HF), the average removal rate was about 138 milliliters per hour, while another trial (UNLOAD) averaged 241 milliliters per hour.
Sessions are not quick. Treatment times across the largest clinical trials ranged considerably: around 12 hours on average in one study, 19 hours in another, 40 hours in a third, and a median of 70 hours in the AVOID-HF trial. These aren’t necessarily continuous stretches. Treatment can be spread over multiple sessions or run intermittently during a hospital stay, depending on how much fluid needs to come off and how fast your body tolerates removal.
Access can be peripheral (a standard IV-type line in the arm) or central (a catheter placed in a larger vein in the neck or groin). A specially designed dual-lumen catheter with coil reinforcement exists for peripheral use with the Aquadex system. Data from one large apheresis center found that 72% of all apheresis procedures used peripheral access, and for elective procedures that number climbed to 80% to 97%. So while central lines are sometimes necessary, most patients can avoid them.
Who Needs Aquapheresis
The primary candidates are people hospitalized with heart failure and severe fluid overload. Fluid overload causes swelling in the legs, abdomen, and lungs, making it hard to breathe, sleep, or function. Most of these patients are initially treated with IV diuretics, which work well for many people. Aquapheresis enters the picture when diuretics aren’t removing enough fluid, when kidneys are too compromised to respond to them, or when the hormonal side effects of high-dose diuretics are creating additional problems.
It has also been studied in other conditions involving dangerous fluid buildup. A clinical trial registered on ClinicalTrials.gov investigated aquapheresis for leukemia patients with severe fluid overload, a scenario where standard approaches may be insufficient or poorly tolerated.
What the Evidence Shows
Several large trials have compared aquapheresis to IV diuretics for hospitalized heart failure patients, with mixed but cautiously promising results. Early studies showed that starting ultrafiltration soon after admission increased total fluid loss and, in some cases, reduced rehospitalizations compared to diuretics alone.
The AVOID-HF trial, the most targeted study to date, randomized 224 patients to either aquapheresis or adjustable IV diuretics. Patients treated with aquapheresis averaged 62 days before their first heart failure event after discharge, compared to 34 days for those on diuretics alone. At 30 days, the aquapheresis group had fewer heart failure and cardiovascular events. However, that difference did not reach statistical significance (p = 0.106), partly because the trial’s sponsor terminated it early after enrolling only 224 of a planned 810 patients. Ninety-day mortality was similar between the two groups.
The 2022 guidelines from the American Heart Association, American College of Cardiology, and Heart Failure Society of America acknowledge that early ultrafiltration can increase fluid removal and may reduce rehospitalizations in some patients. But the guidelines also note that catheter-related adverse events are a concern, and that key questions about patient selection, optimal fluid removal rates, and cost remain unresolved.
Risks and Limitations
The most common risks relate to the catheter itself: infection, blood clots at the insertion site, and bleeding. In the AVOID-HF trial, more patients in the aquapheresis group experienced serious product-related adverse events compared to those receiving diuretics alone.
There’s also the risk of removing fluid too quickly. If the rate of removal outpaces the body’s ability to shift fluid from tissues back into the bloodstream (a process called capillary refill), blood pressure can drop, potentially causing dizziness, fatigue, or kidney stress. This is why clinicians adjust the removal rate throughout treatment rather than running it at maximum speed.
Aquapheresis requires specialized equipment, trained staff, and extended treatment times, all of which add cost. It also keeps patients tethered to a machine for hours or days, which is a meaningful quality-of-life consideration during an already difficult hospitalization. For these reasons, it remains a second-line option rather than a replacement for diuretics in most heart failure care.