[ad_1]
One of the most widely used drugs in the world is not really a medication, at least not in the usual sense.
It's more like a dye.
Doctors call this medicine "contrast", shortcut for contrast agent.
Contrast agents are chemical compounds that doctors use to improve the quality of an imaging test. In the emergency room, where I work, the contrast is most often administered intravenously during a CT scan.
Approximately 80 million CTs are performed each year in the United States and most are performed in contrast.
Most of the contrast agents that I use contain iodine, which can block x-rays. This effect causes illumination of some parts of an image, which greatly improves the doctors' ability to detect items such as tumors, certain types of infections and blood clots.
One thing about contrast agents that differentiates them from conventional drugs is that they have no direct therapeutic effect. They do not make you feel better or deal with what makes you suffer. But they can be crucial to help your doctor make the right diagnosis.
Since these drugs are used in some people who may have nothing wrong, and in others who could be seriously ill, the contrast agents must be relatively safe.
And basically they are. Some patients may develop severe allergic reactions or cardiovascular complications, but these are rare. Others may have nausea or headaches.
But there is an undesirable effect of the much feared contrast: kidney damage. As a result, the contrast is often hidden in patients considered by their doctor to be at risk for kidney problems. The disadvantage is that these patients may not receive the diagnostic information that would be most useful to them.
In recent years, however, new research has led some physicians to question whether this effect has been overestimated.
Is it time to rethink the risk?
The first report of renal injury after intravenous contrast, known as contrast-induced nephropathy, or CIN, was published in a Scandinavian medical journal in 1954. An early form of contrast was administered to a patient for a diagnostic test. . The patient quickly developed renal failure and died. The authors suggested that the contrast was perhaps responsible because they could find no other clear cause at an autopsy.
With other doctors now ready for this eventuality, similar reports began to appear. In the 1970s, renal impairment had become a "well-known complication" of contrast in patients with risk factors for renal failure, such as diabetes. In 1987, intravenous contrast was proclaimed the third leading cause of renal failure acquired in a hospital setting.
The belief that contrast agents were risky had a significant effect on the frequency with which doctors used them. In a survey conducted in 1999 with European radiologists, 100% of respondents thought that CIN involved at least 10 to 20% of patients at risk and nearly 20%, more than 30%. A survey conducted in 2006 found that 94% of radiologists considered that the contrast was contraindicated beyond a certain threshold of renal function, threshold that a US patient of average age on about ten might exceed.
But Dr. Jeffrey Newhouse, professor of radiology at Columbia University, felt that something was wrong with conventional wisdom. He has administered contrast media thousands of times, and it has rarely seemed to him that this product is directly toxic. There were often too many variables involved.
Newhouse has decided to return to primary literature. In 2006, with a colleague, he reviewed more than 3,000 studies on contrast-induced nephropathy and came to an astounding conclusion: only two had used control groups and none of them had found that the contrast was dangerous.
"Everyone has badumed that any kidney damage after contrast was the result of the contrast," said Newhouse, "but these studies did not involve any control group!"
In other words, no group of patients had received contrast media to use for comparison purposes.
Newhouse found that almost all CIN studies had fallen prey to this gap. The importance of controls in any experiment is a basic science; without them, you can not say anything about causation.
What came next was brilliant. "After criticizing those who experienced it without control, we decided to take control without experience," Newhouse said. He reviewed the 10-year data of 32,000 hospitalized patients, but none of them received contrast. He found that more than half of the patients had fluctuations in their renal function that would have met the CIN criteria if they had received a contrast agent.
This raised the possibility that other causes of renal injury – and not the contrast – could have accounted for the badociation found in previous studies.
Other researchers have intensified their research after the publication of Newhouse's findings in 2008. Wisconsin physicians conducted the first major CIN study on a control group in 2009. Out of more than 11,500 patients, the overall Kidney injury was similar between the no ones.
The study, however, presented a major weakness: it was retrospective, that is, it was based on medical records and previously collected data. When a study is conducted in this way, randomization between different treatments can not be used to guard against bias that could skew the results.
For example, if physicians treating patients in the Wisconsin study were worried about contrast with high-risk patients, they might have referred them to the group receiving CT scans without scanning. These sicker patients might have been more likely to suffer from a kidney injury of other origin, which could mask a real difference between the groups.
The next generation of retrospective studies has attempted to use a special statistical technique to control these biases.
The first two appeared in 2013. Researchers in Michigan have found that contrast is badociated with kidney damage in most-at-risk patients, while counterparts in the Mayo Clinic, using slightly more sophisticated methods, have found no badociation between contrast and kidney involvement.
A third study, by Johns Hopkins, was published in 2017. It also revealed no relationship between contrast and kidney damage in nearly 18,000 patients. And in 2018, a meta-badysis of more than 100,000 patients also revealed no badociation.
What did Newhouse do with these results?
"Almost harmless and totally harmless – we are somewhere in between," he says. "But how much harm is done by holding back things? We simply do not know."
Even so, Dr. Michael Rudnick, kidney specialist at the University of Pennsylvania, is not sure that it's time to completely eliminate the contrast agents. He thinks that "there could still be a danger for the most at-risk patients, as discovered by Michigan researchers." And he pointed out that even sophisticated statistical badyzes can not control every possible bias. Only a randomized trial can do it.
Rudnick says that it is unlikely that we would get a randomized controlled trial because it is always possible that the contrast is harmful and that it is unlikely that the ethics committees will approve such a test.
It's an enigma that the existing belief about contrast agents might actually limit our ability to conduct the proper tests to investigate this belief.
Matthew Davenport, lead author of the 2013 Michigan study and chairman of the committee on drugs and contrasts at the American College of Radiology, said that "the vast majority of what we thought was CIN probably was not ".
But he agrees with Rudnick on the fact that there could still be a real danger for most-at-risk patients. He echoed the current recommendations of the American College of Radiology that the decision to use contrast media in patients with pre-existing renal failure should remain an individualized clinical decision.
For now, if you need a scanner that might require contrast, talk about the risks and benefits of the drug for you and make the decision in collaboration with your doctor.
Clayton Dalton is a resident physician at Mbadachusetts General Hospital in Boston.
9(MDA4NDQ0NzQzMDEzMjA3NjYzMThiMzQ4ZQ004))
Source link
