Dual wireless sensors - The chest sensor (left) measures 5 centimeters by 2.5...
Dual wireless sensors - The chest sensor (left) measures 5 centimeters by 2.5 centimeters; the foot sensor (right) is 2.5 centimeters by 2 centimeters. Both sensors weigh as much as a raindrop.
Source: Northwestern University

Wireless sensors monitor babies in NICU

An interdisciplinary Northwestern University team has developed a pair of soft, flexible wireless body sensors that replace the tangle of wire-based sensors that currently monitor babies in hospitals’ neonatal intensive care units (NICU) and pose a barrier to parent-baby cuddling and physical bonding.

The team recently completed a collection of first human studies on premature babies at Prentice Women’s Hospital and the Ann & Robert H. Lurie Children’s Hospital in Chicago and concluded that the wireless infant sensors provided data as precise and accurate as that from traditional monitoring systems. The wireless patches also are gentler on a newborn’s fragile skin and allow for more skin-to-skin contact with the parent.

The study includes initial data from more than 20 babies who wore the wireless sensors alongside traditional monitoring systems, so researchers could do a side-by-side, quantitative comparison. Since then, the team has conducted successful tests with more than 70 babies in the NICU. “We wanted to eliminate the rat’s nest of wires and aggressive adhesives associated with existing hardware systems and replace them with something safer, more patient-centric and more compatible with parent-child interaction,” says John A. Rogers, a bioelectronics pioneer, who led the technology development. “Our wireless, battery-free, skin-like devices give up nothing in terms of range of measurement, accuracy and precision — and they even provide advanced measurements that are clinically important but not commonly collected.”

The new soft, flexible wireless wireless sensors as modeled on a doll.
The new soft, flexible wireless wireless sensors as modeled on a doll.
Source: Northwestern University

The mass of wires that surround newborns in the NICU are often bigger than the babies themselves. Typically five or six wires connect electrodes on each baby to monitors for breathing, blood pressure, blood oxygen, heartbeat and more. Although these wires ensure health and safety, they constrain the baby’s movements and pose a major barrier to physical bonding during a critical period of development.

The benefits of the Northwestern team’s new technology reach beyond its lack of wires — measuring more than what’s possible with today’s clinical standards. The dual wireless sensors monitor babies’ vital signs — heart rate, respiration rate and body temperature — from opposite ends of the body. One sensor lies across the baby’s chest or back, while the other sensor wraps around a foot. (The chest sensor measures 5 centimeters by 2.5 centimeters; the foot sensor is 2.5 centimeters by 2 centimeters). This strategy allows physicians to gather an infant’s core temperature as well as body temperature from a peripheral region. “Differences in temperature between the foot and the chest have great clinical importance in determining blood flow and cardiac function,” Rogers says. “That’s something that’s not commonly done today.”

Traditional NICU sensors as modeled on a doll.
Traditional NICU sensors as modeled on a doll.
Source: Northwestern University

Physicians also can measure blood pressure by continuously tracking when the pulse leaves the heart and arrives at the foot. Currently, there is not a good way to collect a reliable blood pressure measurement. A blood pressure cuff can bruise or damage an infant’s fragile skin. The other option is to insert a catheter into an artery, which is tricky because of the slight diameter of a premature newborn’s blood vessels. It also introduces a risk of infection, clotting and even death. “We are missing a great deal of information where there may be variations in blood pressure over the course of the day,” says neonatologist Dr. Aaron Hamvas. “These variations in blood pressure may have a significant impact on outcomes.”

The device also could help fill in information gaps that exist during skin-to-skin contact. If physicians can continue to measure infants’ vital signs while being held by their parents, they might learn more about just how critical this contact might be. Transparent and compatible with imaging, the sensors also can be worn during X-rays, MRIs and CT scans.

Saving ‘incredibly fragile’ skin

The blood pressure cuff isn’t the only potentially damaging part of current technology. Many premature babies suffer skin injuries from the sticky tape that adheres the wires to the body. Tape can cause skin irritation, blisters and, ultimately, infections. In some cases, this damage can lead to lifelong scarring.

“Premature babies’ skin is not fully developed, so it’s incredibly fragile,” study co-led Dr. Amy Paller says. “In fact, the thickness of the skin in premature infants is about 40 percent reduced. The more premature you get, the more fragile the skin becomes. That means we have to be very careful.”

The Northwestern team has studied 70 babies in the NICU thus far and found no sign of skin damage from the wireless sensors. The sensor’s skin-saving secret lies in its lightweight nature, thin geometry and soft mechanics. The paper-thin device is made from bio-compatible, soft elastic silicone that embeds a collection of tiny electronic components connected with spring-like wires that move and flex with the body. Rogers worked with longtime collaborator and stretchable electronics and theoretical mechanics expert Yonggang Huang to come up with an optimal design.

The wireless sensor communicates through a transmitter placed underneath the crib’s mattress. Using radio frequencies the same strength as those in RFID tags, the antenna transmits data to displays at the nurses’ station. Although it can be sterilized and reused, the sensor is cheap enough (about $10) that it can simply be discarded after 24 hours and replaced with a new one to eliminate any risk of infection.

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