Better baby bonding: Northwestern University develops sensors for monitoring babies in neonatal intensive care units

Northwestern University discusses its research on wireless sensors it has developed for monitoring babies in neonatal intensive care units.

A pair of soft, flexible wireless sensors have been developed to 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 interdisciplinary team from Northwestern University recently completed a series of first human studies on premature babies at Prentice Women's Hospital and Ann & Robert H. Lurie Children's Hospital of Chicago. The researchers concluded that the wireless sensors provided data as precise and accurate as that from traditional monitoring systems, whilst being gentler on a newborn's fragile skin and allowing more skin-to-skin contact with the parent. This study has been published in the journal Science.

The study includes initial data from more than 20 babies who wore the wireless sensors alongside traditional monitoring systems, to allow 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 and more compatible with parent-child interaction," said John A. Rogers, a bio-electronics pioneer, who led the technology development. "We were able to reproduce all of the functionality that current wire-based sensors provide with clinical-grade precision. Our wireless, battery-free, skin-like devices give up nothing in terms of range of measurement, accuracy and precision; they even provide advanced measurements that are clinically important but not commonly collected."

John A. Rogers co-led the research with Dr. Amy Paller, dermatology department chair, Walter J. Hamlin professor of dermatology and professor of paediatrics at Northwestern’s Feinberg School of Medicine, and Dr. Shuai (Steve) Xu, an instructor of dermatology at Feinberg School of Medicine and a Northwestern Medicine dermatologist.

Cutting the cords

Typically, five or six wires connect electrodes on each baby to monitor for breathing, blood pressure, blood oxygen, heartbeat etc. 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.

"We know that skin-to-skin contact is so important for newborns, especially those who are sick or premature," said Paller, a paediatric dermatologist at Lurie Children's Hospital.

New mother frustrated by inability to hold her newborn

After an emergency C-section, Taylor's daughter Grace was rushed to the NICU, where she remained for three weeks. Taylor and her husband felt exhausted when navigating the wires to provide Grace with the most basic care. Grace is among the 70 babies who have participated in the side-by-side comparison study so far.

"Trying to feed her, change her, swaddle her, hold her and move around with her with the wires was difficult," Taylor said. "If she didn't have wires on her, we could go for a walk around the room together. It would have made the entire experience more enjoyable."

Stressful and difficult to take baby out of crib

"The efforts that parents and nurses have to go through just to take the baby out of the crib are astounding," said Dr. Aaron Hamvas, the Raymond and Hazel Speck Berry professor of neonatology at Feinberg School of Medicine, and division head of neonatology at Lurie Children's Hospital.

"Anybody who has had the experience of entering a NICU immediately notices how tiny the babies are, and how many wires and electrodes are attached to them," said Dr. Debra Weese-Mayer, the Beatrice Cummings Mayer professor of paediatric autonomic medicine at Feinberg School of Medicine and chief of paediatric autonomic medicine at Lurie Children's Hospital. "The opportunity to go wireless has enormous potential for decreasing the burden for the nurses, babies and parents."

Going beyond current possibilities

The dual wireless sensors monitor babies' vital signs such as heart rate, respiration rate and body temperature. One sensor lays across the baby's chest or back, while the other sensor wraps around a foot. Each sensor weighs about the same as a raindrop.

"Differences in temperature between the foot and the chest have great clinical importance in determining blood flow and cardiac function," Rogers said.

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," Hamvas said. "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, magnetic resonance imaging and computed tomography scans. "Wires are not just a physical impediment to interacting with the baby but also disrupt imaging if left in place," Paller said. "You can do imaging with the sensors in place and continue monitoring the baby."

Saving 'incredibly fragile' skin

The blood pressure cuff isn't the only potentially damaging part of current technology. Sticky tape that adheres the wires to the body 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," Paller said. "In fact, the thickness of the skin in premature infants is reduced by 40 percent. 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 long-time collaborator and stretchable electronics and theoretical mechanics expert Yonggang Huang to come up with an optimal design. Huang is a Walter P. Murphy professor of civil and environmental engineering and mechanical engineering and professor of materials science and engineering at Northwestern's McCormick School.

"If you look back to the 1960s, the basic approach to monitoring infants is essentially the same as it is today," Rogers said. "It's taped-on sensors, wires to external boxes of electronics. That's all that's ever been done.

"The strength of the adhesive required to keep our lightweight device on the skin is much lower than that of the kinds of adhesives needed to maintain an interface between a hardwired sensor and an external box," Rogers continued. "We have seen no adverse side effects in our study, not even a hint of skin injury even in the most frail babies."

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

When will wireless sensors appear in American hospitals?

Rogers estimates that his wireless sensors will appear in American hospitals within the next two to three years. With support from two major non-profit organisations, Rogers' team expects to send sensors to tens of thousands of families in developing countries over the next year as part of an international effort.