Nearly 6,000 lawsuits against 3M over its Bair Hugger patient-warming device are back in play after a federal appellate court Monday overturned a lower court decision to dismiss them.

A three-judge panel of the U.S. Court of Appeals for the Eighth Circuit ruled that U.S. District Court Judge Joan Ericksen in Minneapolis erred in granting summary judgement in favor of 3M, throwing out suits alleging that the Bair Hugger caused post-surgical infections.

However, on Tuesday, the same three-judge panel upheld a 3M victory in the first and only Bair Hugger trial that was held in 2018 before Ericksen dismissed all of the cases.

In July 2019, Ericksen ruled that all plaintiffs lacked expert evidence showing that their infection theories were supported by generally accepted science. In their appeal, the plaintiffs argued the lower court "abused its discretion" by excluding their medical experts.

The three-judge appellate panel reversed Ericksen's summary judgement, as well as her decision to exclude the medical experts. The appellate court also partially reversed the lower court's decision to exclude the plaintiffs' engineering expert.

"The Eighth Circuit unanimously ruled that the scientific evidence shows that 3M's Bair Hugger can cause deep-joint infections in orthopedic surgeries," said Michael Sacchet, an attorney for the plaintiffs who is with Minneapolis-based Ciresi Conlin.

3M, in a statement, said the court's ruling is "solely procedural," and that the company will "continue to vigorously defend" itself. "We are exploring all next steps and options to challenge the opinion."

3M can appeal the panel's decision to the full Eighth Circuit in St. Louis, which has 11 judges.

In its decision, the appellate court panel didn't dispute Ericksen's determination that there were "weaknesses in the factual basis" of certain opinions by the plaintiffs' medical experts.

However, the appellate judges did not find those medical opinions to be so "fundamentally unsupported" that they should be excluded from trial. The lower court "committed a clear error of judgement" in coming to such a conclusion, the appellate judges wrote.

The Bair Hugger, which was invented in Minnesota, became a big seller in the $1.5 billion market for devices used to prevent hypothermia during surgery. Maintaining a normal temperature during surgery is thought to speed recovery times and enable the body to better ward off infection.

The plaintiffs, however, contend the Bair Hugger promotes infections, because it includes a device that sucks in ambient air from the operating room, warms it, and then blows it into a disposable inflatable blanket draped over the patient.

3M has said the product is safe and that there's no evidence the Bair Hugger causes infections.

Barring the success of any appeal, the Bair Hugger cases will go back for trial in Ericksen's court, where they are part of multi-district litigation (MDL) proceeding. MDLs are used for complex product liability litigation involving many separate federal suits. They usually feature bellwether trials, which set a tone for resolving all claims.

The one bellwether Bair Hugger case that went to trial ended in a victory for 3M.

A federal jury in Minneapolis in May 2018 found that a South Carolina man, Louis Gareis, didn't show that the Bair Hugger caused him to become infected after hip replacement surgery.

Gareis' attorneys at the time said the case wasn't representative of other lawsuits because Ericksen had prevented them from presenting important evidence. They appealed the verdict, citing Ericksen's evidence exclusions.

They also appealed Ericksen's decision during the trial to throw out Gareis' "failure to warn" claim against 3M. The judge only allowed Gareis' "strict liability" claim against 3M to go the jury.

But the appellate panel upheld all of Ericksen's decisions in the Gereis case. In their ruling, they noted that none of the excluded evidence was relevant to the "causation" of Gareis' injury.

And even if it was, "the jury heard extensive testimony about "the many different ways" that the bacteria" causing's Gareis' infection may have entered his body besides the use of the Bair Hugger, the appellate judges concluded.