Medtronic PLC keeps buying, and on Monday it announced the acquisition of technology to prevent sponges, gauze and towels from being left inside patients after surgery.

The Dublin-based company said it would spend $235 million for RF Surgical Systems Inc., a California firm with a proprietary detection system that uses a low radio frequency (RF) signal to track the three surgical supplies.

Medtronic, which has its operational headquarters in Fridley, did not disclose any additional terms for the deal, which is scheduled to close in August.

Medtronic has announced four other deals this year since its $49.9 billion acquisition of hospital supplier Covidien in January.

"Improving patient safety and outcomes is our daily focus, which directly aligns with the RF Surgical technology, a simple and cost-effective solution to avoidable complications in surgical procedures," said Chris Barry, a Medtronic senior vice president, in a statement.

Patient safety concerns have been growing in hospitals for more than a decade. The threat from retained objects in the state is documented each year in a report by the Minnesota Department of Health.

Between 2008 and 2011, there were at least 15 cases per year of retained sponges reported by hospitals, according to the report, although annual tallies dropped to fewer than five in the past two years following more prevention efforts.

Retained objects can lead to harmful complications, so hospital staff typically count items like sponges at the end of surgeries to make sure none have been left inside patients. The high-tech sponges, gauze and towels sold by RF Surgical Systems are meant to be used as an adjunct to manual counting.

They arrive embedded with RF tags that can be detected through blood, dense tissue and bone. Caregivers can use the system as a double-check to see whether a sponge, gauze or towel has been left in the patient.

The system is being used in more than 4,500 operating room, trauma and labor and delivery suites nationwide, said John Barnhill, vice president for marketing at RF Surgical Systems.

The business will be part of the surgical solutions division within Medtronic's minimally invasive technologies group, which includes most of the products acquired from Covidien. The annualized earnings impact for the acquisition is not expected to be material. Medtronic shares gained 80 cents Monday, closing at $75.17.

RF Surgical Systems employs about 60 people. Medtronic employs about 9,300 people in Minnesota.

Twitter: @chrissnowbeck