Simulating womb greatly reduces ROP rate

By Dan Keller

IN 1997, the level 3 neonatal intensive care unit at Cedars-Sinai Medical Centre in Los Angeles, California recognised it had a problem.
It had elevated rates of retinopathy of prematurity (ROP) and an increased need for laser treatment of the condition. So, in 1998 it initiated a strict protocol to curtail oxygen in all very low birth weight infants between 500g and 1,500g.
In utero, babies are in a lower oxygen environment with a blood PaO2 of 22 mm Hg to 24 mm Hg. In full term infants, the level ranges from 70 mm Hg to 90 mm Hg.
High oxygen levels suppress VEGF in the retina and vessels do not grow properly. Ischaemic retina eventually over-stimulates VEGF production and abnormal neovascularisation results.

“When a baby is born prematurely, it enters this environment of oxygen and it’s too much for them. It’s not normal,” paediatric ophthalmologist Kenneth Wright MD said.
By curtailing oxygen at every step for premature infants, the medical centre has been successful in reducing the incidence of severe ROP.
The protocol maintains low oxygen levels and keeps tight control over fluctuations, alarm settings on monitors, clinical responses to alarms and bedside care after increasing oxygen doses.

It stipulates careful regulation of oxygen levels in the delivery room, during transport and throughout the infant’s hospital course. Oxygen saturation levels are kept at 83% to 90% (by pulse oximetry) for infants weighing less than 1000g.
Before 1998, Cedars-Sinai’s incidence of severe ROP was 12.5% of at-risk infants and laser treatment was 7.5%.
After instituting the protocol, Dr Wright said the incidence of severe ROP dropped to 3.72%. In the following three years, only one out of 300 premature infants needed laser treatment.

“There were no cases in 1999 and 2000. In 2002, we had one which required laser surgery. And guess what? That child had a heart defect and the cardiologist put a note on the isolette saying ‘Keep the oxygen high at 95 to 100’. And that’s the only baby that we’ve treated now in four years,” Dr Wright stressed.
The centre has seen a significant decrease in severe ROP. At the same time, infant survival improved slightly from 80.43% in 1997 to 89.47% between 1999 and 2001 (p=0.03).
This suggests that normal vessel growth is occurring, simulating the in utero environment by lowering the oxygen, he said.

Future studies will be needed on cognitive development among premature infants to ensure that solving one problem does not cause another. This research is supported by the Discovery Fund for Eye Research

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