The treatment with xenon gas is experimental and has not been used elsewhere, the doctors at St. Michael's Hospital in Bristol said Friday.
When Riley Joyce was born recently, he couldn't breathe or maintain a pulse, and showed signs of brain injury.
The doctors say they resuscitated him and used xenon gas to cool his brain to reduce the risk of permanent damage. Xenon is a rare, inert gas present in normal air.
Laboratory tests have shown it can double the protective effect of cooling the brain.
After a week, Riley was alert and eating.
Doctors plan to use the gas on at least 12 babies before starting a bigger trial.