Medical therapy does have limitations, so there has been a continued interest in alternative, nonpharmacologic, therapies to address the needs of patients with fluid overload. One such alternative is ultrafiltration, in which a machine with a special filter withdraws blood from a patient's body, removes excess fluid from it and returns the blood to the patient's body.
The use of ultrafiltration for treating fluid overload was first reported in 1974. There are two processes occurring at the same time during ultrafiltration. As excess fluid is removed from the blood vessels, more fluid flows from the tiny spaces in tissues where it has accumulated back into the blood vessels to replace the removed fluid. The goal of ultrafiltration is to keep a constant volume of blood and fluid within the blood vessels while the excess fluid flows back from the tissues into the vessels. In this way, fluid overload in the tissues is relieved, but the volume of fluid and blood in the blood vessels stays level and patients don't develop low blood pressure.
The key to ultrafiltration is the use of a semipermeable membrane (selective filter) through which only some molecules are able to pass -- this depends on a molecule's size and the difference in pressure on the two sides of the filter. Typically, small molecules in the blood, of which one of the most important is sodium (salt), pass through the ultrafiltration membrane. So, the ultrafiltration process doesn't cause changes in the body's levels of certain molecules. In contrast, diuretic medicines can cause an imbalance, which can have adverse clinical effects for the patient.
A group of experts, including Dr. W.R. Clark and colleagues, met in January 2003 to discuss the potential use of ultrafiltration in the management of fluid overload in heart failure patients. The group concluded that, ideally, an ultrafiltration machine -- in addition to being effective and safe -- would be portable and easy to use. It would offer midline and peripheral venous access as alternatives to central venous access (the placement of a catheter in a vein that leads directly to the heart, which is required for kidney dialysis machines). It would be cost-effective for patients, requiring short hospital stays and reducing the readmission rate. A type of ultrafiltration matching the abovementioned criteria was developed and has been shown in clinical trials to be effective in safely removing excess fluid from fluid-overloaded heart failure patients safely.
The use of this type of ultrafiltration was compared to the use of intravenous diuretic drugs to treat fluid overload in heart failure patients in a clinical study called "Ultrafiltration vs Intravenous Diuretics for Patients Hospitalized for Acute Decompensated Congestive Heart Failure" (the UNLOAD study). The study showed that the patients who received ultrafiltration had greater fluid loss than did patients who received intravenous diuretics. They also spent fewer days in the hospital and had fewer repeat hospitalizations for heart failure.
Early measures such as bloodletting, cauterization and Southey tubes paved the way for today's technologically savvy treatments for heart failure, which enable more effective management and improved quality of life for the continually increasing number of fluid-overloaded heart failure patients.
To learn more about ultrafiltration and other ways to manage fluid overload, take a gander at the links on the next page.