March 24, 2000

Infant eye disorder not impacted by extra oxygen: study

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Dr. William Walsh

Infant eye disorder not impacted by extra oxygen: study

Small amounts of supplemental oxygen given to premature infants with a potentially blinding eye disorder may not significantly improve the disorder but definitely does not worsen the condition, a National Institutes of Health study has found.

Vanderbilt University Medical Center was one of the participating 30 centers in the study, which focused on the effect of supplemental oxygen in treating retinopathy of prematurity (ROP). The study was called the Supplemental Therapeutic Oxygen for Pre-threshold ROP (STOP-ROP) study.

The findings, published recently in Pediatrics, mean that clinicians don't have to be as restrictive as they have been when giving supplemental oxygen to infants who have already developed moderate ROP.

Many premature infants need supplemental oxygen soon after birth because their lungs are not sufficiently mature enough to efficiently transfer oxygen into their bodies, said Dr. William F. Walsh, professor of Pediatrics. It has long been believed that supplemental oxygen, while helping infants survive, might also increase the occurrence and severity of ROP.

ROP develops when abnormal blood vessels grow and spread throughout the retina, the nerve tissue that lines the back of the eye. The scarring and bleeding caused by the excess growth can lead to retinal detachment, resulting in vision loss.

"It appears the lack of oxygen in a premature baby causes a call from the retina where the blood vessels grow wildly and become twisted, tear and bleed into the eye," Walsh said. "Giving supplemental oxygen during this period of time after birth causes the blood vessels to grow more orderly and become less likely to tear and to hurt the eye."

ROP occurs in about 14,000 to 16,000 infants each year who weigh less than 2 pounds at birth. In most of those infants, the ROP improves and leaves no lasting damage. But about 1,000 to 1,500 infants develop severe cases of ROP that require surgery. About 225 babies are born at Vanderbilt University Medical Center each year at risk for ROP. However, there are not many babies who actually do go on to develop ROP. In fact, Vanderbilt has such a low incidence that they only enrolled 7 in the study, instead of the estimated 30, and had to drop out of the study.

Walsh said the debate about supplemental oxygen and ROP has been ongoing for more than 50 years. An epidemic of blindness in premature infants in the late 1940s and early 1950s was believed to be associated with the increased amount of oxygen given to the babies. Premature babies during the 50s were usually considered 30 to 32 weeks.

"For 40 years, we have been scared of oxygen use in these premature babies. For awhile supplemental oxygen wasn't given to premature babies and the results turned out to be just as bad, if not worse — death and brain damage from the lack of oxygen," he said.

"During the 60s and 70s, we measured the level of oxygen and for the past 20 years have limited the amount to just enough. We have seen the number of infants born at 25 to 26 weeks increase and they are still having ROP.

So the study, which began in 1994, grouped half of the 649 babies into a group receiving normal amounts of oxygen and half into a group receiving a greater amount. The finding: the eyes of the group receiving higher amounts did not worsen, but also did not improve significantly.

In the group receiving normal amounts of oxygen, 48 percent went on to need surgery. In the group receiving supplemental oxygen, 41 percent required surgery, Walsh said.

"It's just not statistically significant – only seven percent difference and that may not have been from the treatment," he said. "But what this tells us is that we don't need to restrict oxygen. We can give these babies what they need."

The study did find, however, that in the group with supplemental oxygen, 13 percent developed pneumonia or lung damage, compared to 8 percent in the group receiving regular oxygen.

"So we've found that supplemental oxygen is safe but the small benefit may be offset by the worsening of the lung problem."

Walsh said that another study may be needed of a sub-group of the 649 infants studied in the STOP-ROP study. Some of the infants had dilated blood vessels (plus disease). The study found that the infants without plus disease might be more responsive to supplemental therapy than the infants with plus disease.

"That group definitely needs to be studied more," Walsh said.