State and federal investigators continued their investigations yesterday into two tragic operating-room deaths at New Haven’s Hospital of St. Raphael.

The hospital disclosed Wednesday that two women died there during heart surgery last week when they were mistakenly given large amounts of an anesthetic instead of oxygen.

Hospital officials blamed the death on a combination of human error and equipment failure.

The hospital would not release the names of the two women, but The Associated Press identified them yesterday as Doris Herdman, 72, of Southington, and Joan Cannon, 68, of Wallingford. Herdman, who was in poor health, died last Friday; officials became suspicious after the healthier Cannon died during the same procedure Tuesday.

According to a statement released by the hospital Wednesday, an employee or employees plugged a machine that regulates oxygen flow into a receptacle that dispenses nitrous oxide, apparently because the flow regulator was missing an important safety device that would have prevented such a mix-up.

Experts said the kind of mistake is rare.

“I think it is such a rare event that it is not wise to read a lot into it. Even when you take precautions, things can go wrong,” Dr. Lucian Leape, a Harvard researcher who studies medical errors, told The Associated Press.

The hospital would not comment on either of the incidents yesterday and deferred all questions to its written statement.

Officials have said they do not plan to discipline the employees involved, and did not disclose their names.

The company that made the machine, Precision Medical Inc., of Northampton, Pa., did not return phone calls yesterday, despite repeated messages left with the firm’s quality assurance executive.

Both women were undergoing cardiac catheterization, a procedure in which doctors use a flexible tube to inject dye into the heart to check for blockages.

Since both nitrous oxide and oxygen are colorless and odorless, the employee could only have known which gas was which by matching different safety prongs on the receptacles or paying attention to a color-coding scheme, officials at the hospital said.

An autopsy performed yesterday on Cannon did not indicate how she died, but asphyxiation caused by nitrous oxide leaves no readily visible evidence on the body, said Dr. Wayne Carver, the state’s chief medical examiner.

Officials could not perform an autopsy on Herdman because her body had already been buried by the time the incident was reported.

Relatives of both women did not return phone calls by the Yale Daily News. They declined to comment to The Associated Press, but asked that memorial contributions be sent to the American Heart Association.

Officials at the state health department would not say yesterday when they expected to complete their investigation or what kind of disciplinary action, if any, they would take against the Roman Catholic hospital.

The federal Food and Drug Administration will likely conduct its own investigation because the incidents involve a possible defect in a medical device, hospital officials said.