Noninvasive Sensor can Significantly Improve Dialysis

Removing fluid at the precise rate and stopping at the right time is very important for patients suffering from kidney failure and require constant dialysis.

This usually involves guess-work on how much water needs to be removed, and the patient also needs to be carefully monitored for sudden drop in blood pressure.

A present, no easy and reliable method is available to determine hydration levels in such patients, who number about half a million in the U.S. Conversely, a research team from Massachusetts General Hospital and MIT has designed a new, portable sensor that can precisely determine the hydration levels of patients using a method called nuclear magnetic resonance, or NMR, relaxometry.

A device like that would be useful for dialysis patients and also for people suffering from congestive heart failure. The device can also benefit athletes and elderly population who may be at risk of becoming dehydrated, stated 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. This is a way we could measure directly, in every patient, how close they are to a normal hydration state.

Michael Cima, Study Senior Author and Member of Koch Institute for Integrative Cancer Research, MIT

While the new device is predicated on the same technology as MRI (magnetic resonance imaging) scanners, it can achieve measurements in relatively less time and at a fraction of the cost of MRI. This is because imaging is not involved in this process.

The lead author of the paper is Lina Colucci, a former graduate student in health sciences and technology. The study has been reported in in the July 24^th, 2019 issue of Science Translational Medicine.

Other study authors include MIT graduate student Matthew Li; MGH nephrologists Andrew Allegretti, Kristin Corapi, and Herbert Lin; MGH research fellow Xavier Vela Parada; Harvard Medical School assistant professor in radiology Matthew Rosen; and MGH Chief of Medicine Dennis Ausiello.

Hydration Status

Cima started working on this study around a decade ago, after he came to know that there was an urgent need for a noninvasive ad precise method to determine hydration levels. At present, the existing techniques are subjective, invasive, or inconsistent. Most often, physicians assess overload (hypervolemia) by several physical signs like assessing the jugular vein size, examining the ankles where water may collect, or pressing on the skin.

The MIT researchers decided to go for an entirely different technique, predicated on NMR. Earlier, Cima had established a company, known as T2 Biosystems, that utilizes tiny NMR devices to diagnose bacterial infections by examining blood samples of patients.

Cima later devised an idea to apply the devices to determine water content in tissue, and several years ago, the team received a grant from the MIT-MGH Strategic Partnership to conduct a minor clinical trial for tracking hydration. The researchers examined patients with end-stage renal disease who frequently underwent dialysis and also healthy controls.

One major objective of dialysis is to remove fluid from patients and bring them to their “dry weight”. Dry weight is the weight at which the fluid levels of patients are improved. However, it is very difficult to determine a patient’s dry weight. As such, dry weight is estimated by physicians based on physical signs and also via trial-and-error over many dialysis sessions.

The MIT/MGH research team demonstrated that quantitative NMR, which operates by determining a trait of hydrogen atoms known as T2 relaxation time, can enable relatively more precise measurements. The T2 signal determines the environment as well as the amount of hydrogen atoms, or water molecules, present.

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.

Lina Colucci, Study Lead Author and Former Graduate Student, Health Sciences and Technology, MIT

The investigators applied their new device to determine the level of fluid in patients both before and after they went through dialysis. The outcomes demonstrated that this method can possibly differentiate healthy patients from those requiring dialysis with just the initial measurement. Moreover, the measurement precisely demonstrated dialysis patients reaching closer to a usual hydration state over the duration of their therapy.

Additionally, the NMR measurements successfully detected the presence of surplus fluid within the body before conventional clinical signs—for example, the accumulation of visible fluid under the skin—were present. Doctors can use the sensor to establish when a patient has approached his or her actual dry weight, and this determination can be personalized during every dialysis treatment.

Better Monitoring

The scientists are now planning to conduct more clinical trials with dialysis patients. They believe that dialysis, which presently costs the U.S. over $40 billion per annum, would be one among the largest applications for this kind of technology. Such a monitoring can also prove useful for patients suffering from congestive heart failure, which impacts around 5 million people in the U.S, alone.

The water retention issues of congestive heart failure patients are very significant. Our sensor may offer the possibility of a direct measure of how close they are to a normal fluid state. This is important because identifying fluid accumulation early has been shown to reduce hospitalization, but right now there are no ways to quantify low-level fluid accumulation in the body. Our technology could potentially be used at home as a way for the care team to get that early warning.

Michael Cima, Study Senior Author and Member of Koch Institute for Integrative Cancer Research, MIT

According to Sahir Kalim, a nephrologist and assistant professor of medicine at Massachusetts General Hospital, the MIT approach is “highly novel.”

“The development of a bedside device that can accurately inform providers about how much fluid a patient should ideally have removed during their dialysis treatment would likely be one of the most significant developments in dialysis care in many years,” stated Kalim, who was not part of the research. “Colucci and colleagues have made a promising innovation that may one day yield this impact.”

In their analysis of the healthy control subjects, the investigators also observed that dehydration can possibly be detected. This would render the device handy for tracking elderly population, who usually become dehydrated since their sense of thirst reduces with age, or athletes participating in endurance events, including marathons. The team is now planning some upcoming clinical trials so as to test the capability of the novel technology to identify dehydration.

The study was funded by the MGH-MIT Strategic Partnership Grand Challenge, the Air Force Medical Services/Institute of Soldier Nanotechnologies, the National Science Foundation Graduate Research Fellowships Program, the National Institute of Biomedical Imaging and Bioengineering, the Koch Institute Support (core) Grant from the National Cancer Institute, and Harvard University.

(Video credit: MIT)