As people become increasingly comfortable with the use of cellphones, they're beginning to chafe at the remaining restrictions on their use (as anyone who has boarded an airplane recently can attest). The tension over wireless limitations is even more complex in the medical world, where not only do patients and their families want to stay in touch, but wireless connectivity can enable better patient care. A Open Access study that was released today points out yet another complication: wireless technology is a moving target, and what's safe today may not remain so.
The work follows up on an earlier study that suggested that not all cellular technology might be equal when it comes to interference with medical equipment. GSM networks can handle data from two generations of transmission technology: UMTS, and the higher-powered GPRS. The original study suggested that, although UMTS devices were generally safe to have around medical equipment, GPRS-based phones had the potential to interfere with their function.
The new study focuses on what could be considered "worst case" interference. Instead of using typical operating power, the authors reasoned that a hospital environment, which is often deep within a building and subject to a variety of sources of interference, is likely to force phones to operate at their maximal power limits (in the case of GPRS devices, 2 watts). So, they set up both GPRS and UMTS antennae 500cm away from medical devices, and gradually moved them closer while checking the device's function. Problems were classified as light when they simply interfered with monitoring the device, significant when they required intervention, and hazardous when they created a health risk for the patient. Devices included various pumps, monitoring equipment, defibrillators, and pacemakers.
All told, the authors witnessed 48 events, affecting 26 of the 61 medical devices tested. The good news is that cellular devices typically had to be on top of equipment before causing a problem; the mean distance at which signs of trouble appeared was only 3cm. Still, at least one hazardous event occurred out at 300cm (nearly 10 feet), and five happened at 25cm. The key result, however, is the clear relationship between signal power and problems. The UMTS signal, which operates at 10 percent of the power of GPRS devices, caused only 17 percent of the trouble. A low-frequency GPRS signal produced 31 percent of the incidents, while a high frequency version caused about half of the problems. The severity of the problems broke down along similar lines.
The authors note that the existing safety standards of the Netherlands, where the studfy took place, limits cell phones to a distance of over a meter from medical devices, and they suggest this standard is reasonable. But the more notable message is one the authors didn't mention: those standards are clearly going to need to be reevaluated as wireless devices evolve in the future.
Critical Care, 2007. DOI: 10.1186/cc6115