STS: Hyperglycemia After Surgery Seems Okay for Infants

SAN DIEGO, Jan. 30 -- Tight glucose control following cardiac surgery may not be as important in protecting infants' brains as it is for adults postoperatively, researchers said here.

Early postoperative hyperglycemia did not have an adverse impact on neurodevelopment and even tended to yield better cognitive scores by age one year, reported Jean A. Ballweg, M.D., of the Children's Hospital of Philadelphia, and colleagues, at the Society of Thoracic Surgeons meeting.

"In contrast to adult cardiac surgery patients, postoperative hyperglycemia may be beneficial for the developing brain in infants undergoing cardiac surgery," they said in a poster presentation.

Previous studies have shown that hyperglycemia is harmful to the adult brain during ischemia, the researchers said, though animal models suggested the opposite may be true for neonates.

"Lactic acid and metabolic acidosis are handled much differently by a neonatal than an adult animal," Dr. Ballweg said. "Human data are very limited."

So the researchers retrospectively analyzed data from a larger prospective study of genetic polymorphisms' effect on neurodevelopment. They included only the 180 children with glucose values available from the first 48 hours after a single operation for two-ventricle congenital heart disease.

All patients were age six months or younger at the time of surgery (median 76 days). Neonates comprised a substantial proportion (38%) of the patients.

The mean postoperative glucose was 328 mg/dL initially and decreased to a mean of 185 mg/dL for the first 48 hours after surgery overall (range 341 to 95 mg/dL).

When patients were tested for neurodevelopment at age one year, the researchers found no statistically significant association between initial, mean, maximum or minimum glucose levels and scores on the Bayley Scales of Infant Development. The subscale findings were:

• Mean scores on the Mental Development Index tended to be slightly higher with higher postoperative glucose but 95% confidence intervals overlapped (P=0.17).
• Mean scores on the Psychomotor Developmental Index again tended to be slightly higher with higher postoperative glucose but not significantly so (P=0.127).

"Following surgery for congenital heart disease in infants, early postoperative hyperglycemia does not adversely impact neurodevelopmental outcome at age one year," the investigators concluded.

Therefore, tight glucose control may not be necessary for infants, Dr. Ballweg said.

"We don't have any evidence that it's warranted," she said.

However, for older children in the pediatric intensive care unit tight glucose control is standard.

"We don't know what the age threshold is," she said.

The possibility of the blood sugar dropping too low with tight glucose control is of concern particularly for young children, commented Robert Reinhardt, M.D., of St. Joseph Health Center in Kansas City.

"Hypoglycemia in babies carries much more concern than in adults," he said.

While that is true, the findings were still surprising, said Samantha Hill, M.D., of McGill University in Montreal, who also commented on the study.

"I'm surprised that they didn't see any difference," she said. "I'd be interested in seeing a replication study."

Dr. Hill said she was not surprised that the study found neurologic deficits among the entire cohort of infants because cardiac surgery causes damage that can even be seen on an MRI.

The researchers noted several important limitations to their study including that it was a retrospective, secondary analysis of a select group of patients; that glucose values were not obtained at standardized times during the first 48 hours; and that the glucose infusion rate was not standardized or related to blood glucose level.

Also, longer term follow-up will be necessary to determine whether the same patterns are seen with later development.