Mechanical fix for fluid overload

Content provided by the Faculty of the Harvard Medical School

Mechanical fix for fluid overload

During a heart failure crisis, filtering the blood works as well as drugs to remove excess fluid.

Heart failure sends more than one million Americans to the hospital each year, struggling to breathe through fluid-filled lungs. The traditional treatment for helping them get rid of their excess fluid is powerful intravenous drugs that rev up urine production. A machine that filters water and salt from the blood could offer a faster, and possibly safer, alternative.

Heart failure occurs when a weakened or damaged heart can't pump blood efficiently enough to meet the body's needs. The body's amazing ability to keep itself in balance, helped along by drugs and diet, can keep heart failure under control. When it suddenly flares up (what doctors call decompensated heart failure), fluid can fill the lungs or pool in the legs.

The standard remedy, used since the 1960s, is intravenous diuretics. They work by signaling the kidneys to remove more water than usual, which is then urinated away. By getting rid of excess fluid, diuretics ease the workload for a stressed heart. But they can be hard on the kidneys and cause potassium levels in the blood to fall, which can lead to irregular heart rhythms. In addition, some people don't respond to diuretics.

Unloading without drugs

A device called the Aquadex FlexFlow acts a bit like a mechanical kidney — it removes up to a pound of water and salt from the blood an hour. The process is simple. A tiny tube inserted in a vein delivers blood to the machine, where it passes through a special filter. Water and salt go into a waste bag while filtered blood goes back into the body via another small tube. Only about an ounce of blood is outside the body at any time. A person can sit and talk, read, watch television, or snooze while the machine extracts excess fluid.

A trial presented at the American College of Cardiology meeting in March 2006 compared filtration to diuretics. Forty-eight hours after beginning treatment, the people who underwent ultrafiltration had lost 11 pounds of fluid, compared to 7 pounds for those on diuretics. They were also less likely to have low potassium levels. Equally important, the filtration system was just as safe as diuretics.

Over the next 90 days, only 18% of those who underwent ultrafiltration had to be hospitalized for another heart failure flare-up, compared with 32% of the diuretic group.

Although the results are promising, it's still too early to say that ultrafiltration should be used as a standard treatment for fluid overload, says Dr. James Fang, medical director of the heart transplant and circulatory assist program at Harvard-affiliated Brigham and Women's Hospital, who participated in the trial. "The way something works in a clinical trial isn't always the way it works in real life," cautions Dr. Fang. Cost may also slow the adoption of ultrafiltration — treatment with intravenous diuretics costs under $50, while the Aquadex FlexFlow machine costs about $20,000 and each filter runs $800.

That said, the machine could be a good option for people who need to lose a lot of fluid fast, those with kidney trouble, and those who don't respond well to diuretics.

Prevention trumps treatment

Avoiding flare-ups is much safer than treating them. Taking your medicines, checking your blood pressure, watching your salt and fluid intake, and weighing yourself daily can help keep heart failure in check.

Last updated:	September 05, 2008