A small study, done by Dr. A Macario and team at Stanford University tested an RFID-based system for detecting sponges left the surgical cavity.

The study looked at how the new device worked for eight patients at
Stanford University Medical Center. Some tagged and non-tagged sponges
were ‘hidden' inside the patient during an operation by one surgeon,
who asked another surgeon to find them. A battery-operated wand, a type
of detector, was used to find the tagged sponges. The tagged sponges
were very easy to find, say the researchers, while the others were not.

The device detected all sponges correctly, in less than 3 second on
average. There were no false-positive or false-negative results.

The system used was developed by start-up ClearCount Medical Solutions Inc. located in Pittsburg, PA. The company is privately held, founded out of
Carnegie Mellon University to address novel ways of preventing retained
foreign bodies and to improve surgical safety.

In the US, in about 1 in every 10,000 operations that involve an open
cavity, something is left behind in the patient - a total of 1,500
operations each year. This kind of mistake happens more often during
emergency operations. Even though doctors and nurses carefully check
before closing up the patient, the problem still persists, with over
60% of things left inside patients being sponges. Sponges left inside
the patient can go unnoticed for along time, years and even decades -
they can lead to serious and sometimes fatal infections.

I'm surprised they are using passive RFID technology rather than something that would support a more automatic solution, like SAW RFID. ClearCount has a system in development for tracking instruments, and perhaps that will use SAW.

You can read the abstract of the study published in The Archives of Surgery here (Arch Surg. 2006;141:659-662) or you can pay $15 to read the entire study. As an aside, this study was funded by the National Institutes of Health and the vendor. Under pending legislation, this study would be required to appear online (for free) within 12 months of publication.

Pictured right is the ClearCount RFID tag used in the sponges.