NARA, Japan -Two doctors were arrested Saturday over professional negligence in the bleeding death of a patient who was undergoing an operation to remove liver tumours at a hospital in Nara Prefecture in 2006.

The two doctors are accused of failing to prepare blood transfusions or take other safety precautions due to their inexperience in the type of surgery being performed, the Nara prefectural police said.

The tumours were later found to be benign, meaning the patient died from an unnecessary operation.

Police held Fumio Yamamoto, 52, former director of Yamamoto Hospital in Yamato-Koriyama, Nara Prefecture, and Yasuhiko Tsukamoto, the attending doctor for the 51-year-old patient, for professional negligence resulting in death.

Police said Yamamoto, a cardiovascular specialist, and Tsukamoto, an expert on pulmonary surgery, conducted the operation on June 16, 2006, even though neither had performed that type of surgery nor were versed in the proper safety precautions.

Police said they neglected to prepare for blood transfusions before the operation and failed to stop bleeding after blood vessels in the liver were accidentally cut.

In September, police raided Yamamoto's house. Yamamoto told investigators he had never performed liver surgery before.

According to a veteran nurse who worked for the hospital, she warned Yamamoto of the risks, as the liver has a propensity to bleed easily and because Yamamoto was not an expert on livers.

Yamamoto, however, dismissed this advice, saying, "It's an easy operation." The nurse also said Yamamoto, Tsukamoto and two nurses began the operation without preparing transfusion blood.

A medical expert said the operation should have been conducted by seven or eight doctors including an anaesthesiologist and needs about two litres of blood prepared for transfusion - an average operation that opens up the abdomen typically requires 1.5 litres - because the liver, the largest internal organ, contains many blood vessels.

"It's simply unbelievable to conduct a liver operation without having knowledge of how to stop bleeding or expertise of the operation in general," the expert said.

The nurse said Yamamoto disappeared after closing the patient's body following the massive blood loss. The nurse called the prefectural Red Cross blood centre, gave the patient a transfusion and conducted artificial respiration and cardiac massage, but the man was pronounced dead 4½ hours after the operation began.

While trying to save the patient, the nurse tried to get Yamamoto back to the operating room by calling him, but Yamamoto never answered the phone.

The Nara prefectural police opened an investigation into the incident when it was found that the tumors were benign.

A bereaved family member of the patient told The Yomiuri Shimbun, "He might have been used as a guinea pig."

The hospital first told the patient's parents that he died of a heart attack. But last spring, an investigator revealed to the parents that the man died during the operation.

Last month, the Nara District Court ruled that Yamamoto, who is the director of the Yuzankai medical corporation, should be given 2½ years in prison for falsifying catheterization surgeries of welfare recipients to obtain medical fees totaling about 8.3 million yen between 2005 and 2007. He has appealed the ruling.