Hospital Quality Affects Survival for Very Small Newborns

STANFORD, Calif., May 23 -- Very-low-birth-weight infants are more likely to survive if they are born at hospitals that have high-performing neonatal intensive care units with a large volume of patients, researchers reported.

An estimated 21% of infants weighing less than 1,500 g might have lived had they been born in such a hospital, reported Ciaran S. Phibbs, Ph.D., of Stanford, and colleagues, in the May 24 issue of the New England Journal of Medicine.

Less than a quarter of these high-risk infants were born in hospitals with high-level and high-volume NICUs in 2000, and this percentage has been declining, especially with the spread of NICUs to community hospitals. Dr. Phibbs zand colleagues wrote. Most of the new NICUs in California in the 1990s were low- or moderate-volume.

To study the differences in neonatal mortality among various NICUs in California hospitals, the investigators linked birth certificates, hospital discharge abstracts, and fetal and infant death certificates to assess neonatal mortality rates among 48,237 very-low-birth-weight infants born from 1991 to 2000.

In the study, levels of care, for example, included provision of mechanical ventilation or neonatal surgery (open heart, cardiopulmonary bypass, or extracorporeal membrane oxygenation).

Infant-mortality rates among the infants varied according to both the volume of patients and the hospital's level of care, the researchers said. The effect of volume also varied according to the level of care,

Mortality was lowest when very-low-birth-weight deliveries occurred in hospitals with tertiary-level NICUs that treat more than 100 of these infants annually. However, only 35.6% of these infants were born in such facilities in 1991, and 21.5 % in 2000.

Compared with a high level of care and a high volume of very small infants (more than 100 a year), lower levels of care and lower volumes (50 or fewer infants a year) were associated with significantly higher odds ratios for death, ranging from 1.19 (95% confidence interval, 1.04 to 1.37) for level 3B, C, or D with 51 t 100 births per year to 2.72 (CI, 2.37 to 3.12) for level 1 with fewer than 10 births per year.

In this analysis, two small groups of hospitals (seven facilities) were excluded, the researchers noted, because the hospitals had either no use or restricted use of mechanical ventilation. Statistical tests showed that they should not be combined with smaller NICUs with the same level of care, the researchers said.

A NICU that treats 50 very-low birth-weight infants a year corresponds to an average census of about 15 patients. Thus, most of the increase in the risk of death was accounted for by hospitals with small to moderate-size NICUs, the researchers said.

Although the associations between mortality and NICU level and volume were greater for infants less than 1,000g, they were still significant for larger infants.

Less than one quarter of these high-risk deliveries occurred in high-level, high-volume facilities, yet 92% of very-low-birth-weight deliveries occurred in urban areas with more than 100 such deliveries, the researcher reported. This suggests that it would be geographically feasible to regionalize the vast majority of these deliveries in California.

The authors estimated the potential effect of shifing infants to hospitals with hign level of care. "Assuming that only 90% of the deliveries of very-low-birth-weight infants in the large urban areas could be shifted to hospitals with tertiary-level NICUs that care for at least 100 such infants annually, we estimated that 21% of the deaths of very-low-birth-weight infants in the year 2000 were potentially preventable," they wrote.

To do so, they said would probably require the addition of some large perinatal centers to maximize geographic access. This could be created by the merger of existing, smaller NICUs.

Although it might be harder to do this in more sparsely populated areas of the U.S., this study, they said, suggests that reductions in mortality might be achieved by moving from low to more moderate volumes, possibly a more feasible goal in these areas.

Discussing the study's limitations, the researchers said that because of its observational design, factors other than NICU quality may explain neonatal mortality. For example, hospitals with large, high-level units may also have better obstetrical care. The ability to provide rapid emergency cesarean section not only prevents some fetal deaths but may result in healthier infants.

Although the study controlled for many potential confounders, data were limited to information from birth certificates and discharge abstracts. In addition, the only outcome assessed was mortality, yet other outcomes, such as intraventricular hemorrhage and chronic lung disease are also important, the researchers wrote.

"Our results suggest that increased regionalization of perinatal care might reduce mortality among very-low-birth-rate infants," the investigators concluded.