Hydration sensor benefits dialysis patients

Patients undergoing kidney dialysis must have their hydration level closely monitored; a newly-developed portable sensor makes it
Patients undergoing kidney dialysis must have their hydration level closely monitored; a non-invasive portable sensor makes it easier (Bing)

The key for successful dialysis for patients with kidney failure is the proper timing and amount of fluid removal. But determining the correct level of patient hydration has up to now been guesswork. Researchers from MIT and Massachusetts General Hospital have now developed a portable sensor that can accurately measure patients’ hydration levels, using a technique known as nuclear magnetic resonance (NMR) relaxometry.

MIT researchers have developed a portable sensor that can accurately measure patients’ hydration levels, using a technique known as nuclear magnetic resonance (NMR) relaxometry.
MIT researchers have developed a portable sensor that can accurately measure patients’ hydration
levels, using a technique known as nuclear magnetic resonance (NMR) relaxometry.

Such a device could be useful for not only dialysis patients but also people with congestive heart failure, as well as athletes and elderly people who may be in danger of becoming dehydrated, according to Michael Cima, the David H. Koch Professor of Engineering in MIT’s Department of Materials Science and Engineering.

“There’s a tremendous need across many different patient populations to know whether they have too much water or too little water,” said Cima, senior author of the study and a member of MIT’s Koch Institute for Integrative Cancer Research. “This is a way we could measure directly, in every patient, how close they are to a normal hydration state.”

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Cima began working on this project about 10 years ago, after realizing that there was a critical need for an accurate, noninvasive way to measure hydration. Currently, the available methods are either invasive, subjective, or unreliable. Doctors most frequently assess overload (hypervolemia) by a few physical signs such as examining the size of the jugular vein, pressing on the skin, or examining the ankles where water might pool. 

The MIT team decided to try a different approach, based on NMR. Cima had previously launched a company called T2 Biosystems that uses small NMR devices to diagnose bacterial infections by analyzing patient blood samples. One day, he had the idea to use the devices to try to measure water content in tissue, and a few years ago, the researchers got a grant from the MIT-MGH Strategic Partnership to do a small clinical trial for monitoring hydration. They studied both healthy controls and patients with end-stage renal disease who regularly underwent dialysis.

The portable device is based on the same technology as magnetic resonance imaging (MRI) scanners, but can obtain measurements at a fraction of the cost of MRI, and in much less time, because there is no imaging involved.

Lina Colucci, a former graduate student in health sciences and technology, is the lead author of the paper published on the research, which appeared in the July 24 issue of Science Translational Medicine.

“The beauty of magnetic resonance compared to other modalities for assessing hydration is that the magnetic resonance signal comes exclusively from hydrogen atoms. And most of the hydrogen atoms in the human body are found in water molecules,” Colucci says.

Hydration status. (Michael Cima, MIT)

The researchers showed that quantitative NMR, which works by measuring a property of hydrogen atoms called T2 relaxation time, can provide much more accurate measurements. The T2 signal measures both the environment and quantity of hydrogen atoms (or water molecules) present.

The results showed that this technique could distinguish healthy patients from those needing dialysis with just the first measurement. In addition, the measurement correctly showed dialysis patients moving closer to a normal hydration state over the course of their treatment. Furthermore, the NMR measurements were able to detect the presence of excess fluid in the body before traditional clinical signs — such as visible fluid accumulation below the skin — were present. The sensor could be used by physicians to determine when a patient has reached their true dry weight, and this determination could be personalized at each dialysis treatment.

The researchers are now planning additional clinical trials with dialysis patients. They expect that dialysis, which currently costs the United States more than $40 billion per year, would be one of the biggest applications for this technology. This kind of monitoring could also be useful for patients with congestive heart failure, which affects about 5 million people in the United States.

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