Copyright 2002 The New York Times Company
The New York Times
June 16, 2002
Risk Seen in Move To Replace Gauge Of Blood Pressure
By GINA KOLATA
Across the nation, hospitals and doctors' offices are returning blood pressure cuffs to their manufacturers to comply with a federal environmental initiative to cut down on the use of mercury, a toxic metal that can pollute the air and water when disposed of improperly.
But leading medical experts, joined by the American Heart Association and the National Heart, Lung and Blood Institute, say the mercury gauges are being replaced by newer devices that may be unreliable, and they warn that inaccuracies may be leading to false diagnoses and inappropriate treatments. Nobody knows how many hospitals and doctors have abandoned the old blood pressure cuffs. Nor is it known how well the newer devices are performing. Anecdotal evidence from doctors suggests that erroneous pressure readings have caused illness and death, but some medical centers, including the Mayo Clinic, say other devices have been reliable.
Still, experts are alarmed enough to call for a pause in the rush to install the newer devices. In a joint statement, the heart association and the Heart, Lung and Blood Institute (one of the National Institutes of Health) say that before the old mercury devices are removed, the nation needs a system to be sure the new ones are accurate and reliable.
"We've been caught off guard," said Dr. Daniel W. Jones, a blood pressure expert at the University of Mississippi Medical Center who is a spokesman on high blood pressure for the heart association. "We don't have a system in place to ensure the accurate determination of blood pressure."
Dr. Claude Lenfant, the director of the Heart, Lung and Blood Institute, agreed, saying, "It is clearly a matter of public health."
The push to get rid of mercury sphygmomanometers, as the devices are known, began in June 1998, when the Environmental Protection Agency and the American Hospital Association agreed to eliminate as much mercury waste as possible from hospitals by 2005. Others, including medical clinics and many doctors' offices, joined the effort, getting rid of such things as thermometers and batteries that contained mercury.
The use of mercury devices remains legal. Environmental and medical experts say they are not a leading cause of mercury contamination, though they add that a spill from a broken sphygmomanometer can be expensive to clean up.
Even so, manufacturers say thousands of the old gauges are being returned and demand for new mercury ones is drying up. "Our business has suffered substantially," said John Baum, president of the Baum Company of Copiague, N.Y.
There are several alternatives to the mercury gauges, all producing the familiar numerical readings of pressure when the heart beats and when it rests between beats. Aneroid devices -- the term means "without liquid" -- use metal that acts like a spring to measure blood pressure. Automatic devices measure pressure in a variety of ways, including converting pressure readings into measurable electronic waves.
The Food and Drug Administration, which regulates medical devices, has no official standards that companies must follow for approval of ones that measure blood pressure. But it says that in practice, companies use tests that include making sure that a prototype of a device accurately measures blood pressure in repeated laboratory tests.
Edward Wright, a vice president at Welch Allyn Inc., which makes all three types of blood pressure devices -- mercury, aneroid and electronic -- says all are effective. "These are highly accurate instruments when they are shipped," Mr. Wright said.
But the mercury device has long been the gold standard. If properly maintained, it can give accurate readings for decades.
Dr. Jones, speaking for the heart association, said it was still the preferred device. But now, he added, "for the first time in 100 years we are faced with some places' not having mercury manometers available for blood pressure measurements."
Dr. Edward Roccella, the coordinator of the institute's National High Blood Pressure Education Program, said there was no requirement that the devices be proved accurate under constant use. Nor must they be proved reliable for patients of a variety of ages, illnesses and sizes. Without vigilant monitoring, there is no way to know when they go awry.
The metal in the aneroid devices can fatigue, making readings inaccurate. So manufacturers recommend that they be recalibrated every six months or so, often asking that they be returned to the companies for service. But Dr. Roccella says that is seldom done.
Electronic devices use physical measurements and mathematical formulas to calculate pressure, but some blood pressure experts say they are unsatisfied by the data that the companies provide.
"What is the accuracy of these and how are they recalibrated?" Dr. Roccella asked. He said that because companies keep the algorithms secret from competitors, it is impossible for outsiders to independently assess the devices.
"This is not to say that the new digital devices cannot be accurate. And it is not to say that aneroids can't be useful," he said. "But how do we know that this is so?"
In the meantime, hospitals and medical centers are switching from mercury devices and are making their own decisions about how carefully to assess their equipment.
Some say that they have been able to rid themselves of mercury sphygmomanometers with no problems.
The Mayo Clinic switched to aneroid devices and checks them annually, said Dr. Sheldon Sheps, an emeritus professor of medicine there. He said a study by the clinic's doctors looked at 248 aneroid devices, 17 percent of the 1,500 in use at two Mayo Clinic hospitals. Only one needed to be replaced.
Others were less sanguine.
"Sometimes these devices give readings that are very wrong," Dr. Jones said, adding that the errors can be 30, 40, even 50 points.
At a recent meeting, Dr. Jones described the case of an elderly woman who was receiving high doses of blood pressure lowering drugs for what looked like an alarmingly high reading. Her systolic pressure, the pressure on vessels when the heart contracts, was 170 millimeters. Normal is 120.
Her pressure had been measured with an electronic device. When it was tested with a mercury sphygmomanometer, it actually was 90. In trying to lower what they thought was a dangerously high blood pressure, the woman's doctors had made her pressure so low that her brain did not get enough blood. As a result, Dr. Jones said, she had a stroke.
Dr. Clarence E. Grim, a blood pressure expert at the Medical College of Wisconsin, said doctors at an obstetrician's office near his hospital used were using an aneroid device that was consistently giving gave readings 30 points too low.
At Hartford Hospital in Connecticut, where the mercury sphygmomanometers have been replaced with aneroid devices, one cardiologist, Dr. Paul Thompson, got permission to buy and keep three mercury devices for himself.
Eric Rosow, director of biomedical engineering at Hartford Hospital, said his group bought the devices from a reliable company. The hospital then checked them against mercury sphygmomanometers. Now, he said, the group examines them quarterly to be sure that the dials read zero when they are not in use.
Dr. Thompson is not assuaged. Recently, he said, he referred a patient for a test of her arteries that required taking nitroglycerin. The testing laboratory said "they couldn't do it because her blood pressure was 90," he recalled. "I said, 'Her blood pressure was never that low.' "
Dr. Thompson told the technicians to measure the woman's pressure again with a different device. This time, it read 120.
"This is just a major, major thing," he said. "Soon we won't know what anyone's blood pressure is."