A wearable sensor being developed at the University of Michigan (UM) www.engin.umich.edu may be able to provide doctors with the first simple, portable, non-invasive way to measure fluid status which is the volume of blood coursing through a patient’s blood vessels at any given time.
Fluid status is a diagnostic measure much like heart rate or blood pressure. Knowing the fluid status can be used to alert doctors when a cardiac patient has excess fluid that prevents their heart from pumping efficiently or it enables doctors to have a more precise measure of how much waste fluid to filter out of a dialysis patient’s blood. It can also tell doctors how much fluid to give to a trauma patient who has lost blood or to a septic patient with an overwhelming infection.
Currently, getting an accurate measure of fluid status requires an ultrasound or the insertion of a specialized catheter to measure the pressure of blood flowing through a blood vessel. Both tests are expensive, complex, and must be administered in a hospital by an expert.
The new sensor under development at UM could make measuring fluid status as simple as strapping a smartphone-sized device to a patient’s arm or leg and asking them to take a deep breath. Because it can be worn for extended periods of time, the device could provide doctors with an unprecedented amount of real-time data about fluid status.
The device uses a process called “Dynamic Respiratory Impedance Volume Evaluation” or DRIVE to measure the changes in electrical conductivity of the wearer’s limb as they breathe. Blood conducts electricity, so that a patient with more blood will have greater conductivity. This device is the first to incorporate fluid status measurement into a wearable device.
“This could turn fluid status into a routine diagnostic tool and the potential to improve care and lower costs for millions of patients,” said Kevin Ward, Executive Director of the UM Center for Integrative Research in Critical Care www.micircc.org. The Center provided funding along with the Baxter Healthcare Corporation www.baxter.com to develop the device.
The team has been testing a benchtop version of the sensor built from off-the-shelf components for more than a year. The new study will compare the accuracy of the wearable sensor to that of the conventional ultrasounds of the vena cava in patients undergoing dialysis or intensive care.