A Wayne State University School of Medicine pediatrician led a nationwide study that has determined the definitive safest depth and duration of body cooling to minimize injury in newborns deprived of oxygen during birth.
Seetha Shankaran, M.D., professor of Pediatrics and pioneering researcher of the technique to reduce injury from hypoxic ischemic encephalopathy, led the study that now delineates the acceptable temperature and length of that cooling. Published in the Journal of the American Medical Association, the results complete 20 years of research into the cooling technique.
The study, which involved 364 infants during a six-year period, determined that the safest depth and duration of hypothermia treatment - using a specially-designed "cooling blanket" - consists of lowering the oxygen-starved newborns' body temperature to 33.5 degrees Celsius for a period of 72 hours.
"Neither longer cooling nor deeper cooling nor both were more superior to cooling for 72 hours at 33.5 degrees Celsius in reducing death or survival with disability at 18 months of age," said Dr. Shankaran, who also serves as a neonatologist for Children's Hospital of Michigan and Hutzel Women's Hospital.
The finding is significant and surprising, Dr. Shankaran said, because earlier studies using animal models had suggested that lowering the temperature to 32 degrees Celsius and for a longer period (120 hours) might provide better injury protection.
The study reports the outcomes assessed during the neonates' stay in the neonatal intensive care unit. Those who survived were followed up to 18 months of age to examine the effect of longer or deeper cooling on overall rate of death or disability, the primary outcome of the study.
Hypoxic ischemic encephalopathy occurs in approximately one in 1,000 full-term births in the U.S. each year as a result of interrupted blood-flow and lack of oxygen. The condition can be caused by problems as such as umbilical cord strangulation, placental abruption, cardiac or respiratory arrest in the mother during delivery or other disorders that decrease delivery of blood-borne oxygen to the infant during birth.
Between 15 percent and 20 percent of affected infants will die in infancy or early childhood. Another 25 percent will develop severe and permanent neuropsychological deficits, including mental retardation, visual or motor dysfunction, epilepsy or cerebral palsy.
For Dr. Shankaran, whose landmark 2005 study in the New England Journal of Medicine helped to make the 72-hour "cooling blanket" procedure the standard of care in treating HIE, the publication of the new trial was "a very encouraging step forward.
"I think we have shown clearly and with a great deal of accuracy that using whole-body cooling in the neonatal period at 33.5 C for 72 hours is safer than either longer cooling, deeper cooling or both."
The results should have an immediate positive impact on clinicians who treat HIE-affected newborns in neonatal intensive care units. Clinicians should avoid cooling for either longer duration of time or for a greater depth.
Dr. Shankaran said the latest findings could not have occurred without "the tremendous amount of work that was done by all of the researchers in the Neonatal Research Network, or without the public dollars provided for this effort over the years by the National Institute of Child Health and Human Development."