The number of medical mistakes in Minnesota hospitals fell slightly last year and were generally less severe than in previous years, but a new report from the Minnesota Health Department shows preventable errors still are happening.

There were 301 serious mistakes reported to the department last year and four people died, according to the sixth annual “Adverse Health Events” report released Thursday. The total was down 3.5 percent from the year before. Four deaths are the fewest since the reports began; the high was 24 in 2006.

The number of mistakes resulting in serious harm or death was 98, down from 116 the year before. Preventable falls that cause significant injury, one of the most commonly reported incidents, fell 20 percent from the previous year to 76.

“We are having fewer events resulting in serious harm,” said Health Commissioner Dr. Sanne Magnan. “The severity is going down so there’s less harm to patients. That’s the bottom line here.”

Of the deaths, one was considered a preventable suicide in a hospital, one was considered a surgical error and two were attributed to the onset of hypoglycemia, or low blood sugar.

The report gives a glimpse into the mistakes made by 199 hospitals and surgical centers and the health care industry’s attempts to correct them.

It covers 28 reportable events from October 2008 to October 2009.

When Minnesota issued its first report of medical errors in its hospitals in 2003 it was the first state to do so. Diane Rydrych, assistant director of the department’s health policy division, said 27 states now have some sort of report, but Minnesota’s is the most detailed.

Magnan said the extensive reporting encourages the hospitals to learn from each other and empowers patients to look out for themselves.

“We are being extremely transparent about it because we think that is what is helpful,” she said. “We think this kind of transparency and openness is good for patient safety in Minnesota.”

Sandra Potthoff, a professor of health care administration at the University of Minnesota, agreed. She said little can be learned from a single error at a single hospital, but when all the data is put together, trends emerge.

“It’s hard to learn from an (sample) of one,” she said.

One lesson learned in the latest report was on the cause of many bedsores, also called pressure ulcers, as hospitals were asked to give more detail in that category. The analysis found a quarter of them could be traced to medical equipment rubbing against the skin, such as neck collars and oxygen masks.

Another 13 percent were tied to long surgical procedures when the patient is immobilized.

The total number of serious bedsores remained constant from 2008, at 112.

There were 44 reported surgeries or other invasive procedures performed on the wrong patient or wrong body part, up slightly from 39 the year before. About 60 percent of those accidents happened in operating rooms; the rest were in other parts of the hospitals, including the cardiology and radiology departments.

Most hospitals have operating room protocols designed to prevent such errors. Rydrych said the reasons for the persistent errors in operating rooms are complicated, but can often be attributed to simple human error despite a greater focus on eliminating mistakes.

She said hospitals also are being more diligent about reporting errors outside surgery. For example, if someone put in the wrong sized catheter at a patient’s bedside it would be considered a reportable mistake, she said.

“We’re making really good progress in the O.R., but culture change takes time,” she said.

In one common procedure in operating rooms, she said the whole surgical team stops to double check the patient’s medical history, identity and the surgery site. It’s a policy she would like to see expanded beyond the operating room.

Lawrence Massa, president of the Minnesota Hospital Association, said his members would work to bring down the numbers of wrong procedures or wrong patients. “That just tells use they need to expand the protocols that we use in the O.R.,” he said.

The number of foreign objects — including sponges, gauze and bits of medical devices — left in bodies after surgeries and other invasive procedures was 38, up just one from the year before.