A Better Measure of Unborn Babies' Health

Originally Published MDDI June 2002

MEDICAL DESIGN EXCELLENCE AWARDS 2002

OxiFirst Fetal Pulse Oximetry System

Submitted and manufactured by Nellcor, a Tyco Healthcare company (Pleasanton, CA)

During nearly one-third of all childbirths in the United States, the fetus presents an abnormal heart-rate pattern. Such abnormal patterns may be caused by a dangerous lack of oxygen to the baby or by another circumstance, such as the fetus falling asleep. Conventional fetal heart-rate monitors fail to distinguish between the two situations, leaving obstetrical teams to guess about whether they need to intervene on behalf of the fetus, perhaps by giving the mother extra oxygen or delivering the baby by caesarean section.

Nellcor's OxiFirst Fetal Pulse Oximetry System introduces a technology that helps take the guesswork out of how well an unborn baby is coping with delivery.

"Fetal heart-rate readings can be ambiguous and subject to different interpretations by different doctors. Our technology provides a continuous, direct, objective measure of the fetus's blood oxygenation level, information that previously was not available," explains Madeleine Bolling, Nellcor's perinatal product manager.

"By also providing readings of the oxygen saturation level, our product gives clinicians a more accurate representation of the fetus's well-being," adds Paul Mannheimer, physicist and principal scientist at Nellcor.

When a fetal heart-rate monitor displays an ambiguous or nonreassuring fetal heart-rate pattern, the OxiFirst system is employed by inserting a single-use sensor into the birth canal. The sensor rests against the fetal cheek, forehead, or temple, and harmless red and infrared light shines onto the baby's skin and is then reflected back, captured, and analyzed. Fetuses with an oxygen saturation level greater than 30% are in the normal range and generally don't require intervention, Mannheimer says.

While pulse oximetry has been in use for decades, this new application was first conceived by Nellcor's founders in the early 1980s. By the late 1980s, the project was in active development, but it took nearly 15 years before a solution was introduced to the marketplace in summer 2000.

"We faced four major challenges," recalls Mannheimer. "First was how to attach a sensor to the baby in a wet environment where you can't see what you're doing. In early designs, we slid the sensor just under the cervix, and then we tried vacuum attachments. In both cases, we could not get reliable readings because some fetuses have lots of dark hair, making it difficult to pick up signals. We finally succeeded by moving the sensor farther along the head, past the hair, letting the uterine wall hold it in place using a fulcrum tip. We also had to develop a feature that would let doctors know if the sensor lost contact with the fetus's skin. We added small electrodes to the front of the sensor that would measure whether the sensor is touching the skin or floating in amniotic fluid, so the clinician doesn't have to see exactly where the device is to know that it's in proper contact."

A second challenge involved picking up the very weak fetal signals. Nellcor had to change the electronics since fetuses' arterial pulse amplitudes are typically 2 to 10 times smaller than those seen when monitoring adult fingers (the most common site used in adult monitoring). The sensors also had to be specially designed and calibrated to read fetal saturations—levels that are dramatically lower than adult values.

A final design challenge resulted from not knowing the ideal levels of oxygen saturation for fetuses in utero since the subject had never before been addressed. Engineers and clinicians worked together for years, conducting studies in animals and humans to determine the critical threshold. They found that fetuses with a saturation level above 30% are well oxygenated, reports Bolling.

By persevering in refining current technologies into a new application, Nellcor has made it possible for obstetrical teams to make delivery decisions with increased confidence.

Copyright ©2002 Medical Device & Diagnostic Industry