3M / Bair Hugger Forced-Air Warming Blanket Infection Litigation

The Bair Hugger is a forced-air warming system used in hundreds of thousands of surgeries annually in the United States to maintain patient body temperature during procedures. Plaintiffs in this MDL allege that the device draws in contaminated floor-level air — laden with bacteria and other pathogens — and recirculates it across the sterile surgical field via warm air currents, significantly increasing the risk of deep periprosthetic joint infections (PJIs). These infections, which occur around implanted hip or knee prosthetics, can be catastrophic, requiring multiple revision surgeries, prolonged IV antibiotic treatment, and in some cases amputation. The litigation began in earnest after a prominent 2015 study published in the Journal of Bone and Joint Surgery raised alarms about infection rate disparities between hospitals using forced-air warming versus conductive warming blankets.

3M has vigorously contested the scientific evidence, and in 2019 the MDL court granted summary judgment in 3M's favor in the consolidated 'general causation' bellwether track, ruling that plaintiffs had not presented sufficient expert evidence to establish that Bair Hugger caused infections. Plaintiffs appealed, and the Eighth Circuit Court of Appeals reversed the ruling in 2021, reinstating thousands of cases and finding that the district court had applied too strict a standard in excluding plaintiffs' experts. The litigation has continued since then, with individual cases proceeding and ongoing disputes over expert testimony, making this one of the most complex and long-running medical device MDLs in the country. No global settlement has been reached as of 2025.