Looking for trouble in medical devices

Looking for Trouble in Medical Devices

On Oct. 28, 1983, three people went to the same kidney dialysis center in Dallas for their three-times-a-week treatment to cleanse their blood of impurities their own kidneys could not remove. Within minutes of being attached to the center's multiple patient dialysis machine, all three were dead--their blood overheated by the unit.

The machine was designed to mix water with the necessary chemicals to produce dialysate, the fluid that removes waste products from a patient's body during dialysis. The unit is supposed to heat the fluid to the correct temperature and pump it to individual dialysis units, where the actual filtering of the patient's blood occurs. But in the Dallas case, the dialysate overheated, the machine's alarm system failed, and the overheated dialysate caused the patients' blood to overheat in turn.

The dialysate is normally heated to body temperature by a gas heater or, if that fails, a backup electric heater. In the Dallas incident, dirt or other debris apparently got into the control mechanism for the electric heater and switched it on while the gas heater was still operating. The result: overheated dialysate. The control board, designed to prevent the overheated dialysate from increasing the patients' blood temperature, failed. With the control board broken, the alarm system, which should have alerted the attending nurses, also failed, allowing the dialysate to overheat the patients' blood.

To unravel the tangle of failures that led to the three deaths, FDA's Mechanics and Materials Laboratory was called on to examine the faulty dialyzer. The lab, which was moved in 1984 from cramped, obsolescent quarters in Washington, D.C., to new facilities in suburban Rockville, Md., is equipped to study a wide variety of medical devices, from eyeglasses to artificial heart valves. The staff of engineers and scientists can employ any of a number of techniques, such as electron microscopy and laser imaging, to find out why a certain device failed, or even why it might fail in the future. The staff's expertise at probing the intricacies of modern medical high-technology is a key contributor to FDA's mission in ensuring the safety and effectiveness of medical devices.

"It turned out there were a number of problems involved (with the dialyzer), not the least of which was a miswired circuit,' states Ed Mueller, deputy director of the lab. The wiring error caused a transformer to put out 40 volts instead of the 20 volts it should have produced. This problem was masked by a voltage regulator diode designed to protect the dialysis machine's circuitry from power line surges. The diode failed that day, and the increased voltage knocked out the control board that monitored the dialysate temperature and controlled a diverter valve, which would have disposed of the overheated dialysate.

"The dialysis center got lucky; then they got unlucky,' says Mueller. The voltage regulator diode had held the increased voltage down for seven years without a problem, until it failed from being continuously overstressed.

After the lab had pinpointed the problems, FDA required the manufacturer to visit all known machine users to check for miswired circuits and any other flaws. In Michigan, the manufacturer found and repaired one other miswired unit that hadn't failed. FDA continues to monitor dialysis machines from all manufacturers.

In addition to solving such life-threatening cases, the lab focuses on preventing public health problems. As one of five laboratory divisions within the Center for Devices and Radiological Health, the Mechanics and Materials Laboratory (also known as the Division of Mechanics and Materials Science) also helps develop performance criteria for anesthesia machines; household medical products like toothbrushes, eyeglasses and tampons; and many other devices.

Other laboratory divisions within the center include: Biometric Sciences, which reviews and evaluates medical device statistical data; Life Sciences, which conducts research on the health effects of radiation and medical devices; Physical Sciences, which conducts engineering studies related to the safety and effectiveness of medical devices and electronic products; and Electronics and Computer Sciences, which provides electronics and computer science support for medical device and radiological product programs.

The role of the Mechanics and Materials Lab, according to Director Don Marlowe, is to ensure that the best scientific knowledge available is used in the design of each device. The lab evaluates device performance data that are submitted as part of new device approval applications. It also conducts research to develop better techniques for manufacturers to analyze device performance.

The lab checks devices for:

Strength--Is the device strong enough so that it will not break during normal use?

Material composition--If the device is to be implanted in the body, is it made of appropriate material so that body fluids will not cause it to break down?