June 20 (UPI) -- A randomized, controlled trial in China recently found that patients who inhaled nitric oxide during and for 24 hours after heart surgery saw a decreased risk of developing acute and chronic kidney problems.
The study, published in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine, is the first to show a drug could reduce kidney injury resulting from heart surgery, the researchers say.
Previous studies have shown that prolonged cardiopulmonary bypass can disrupt circulating red blood cells and the release of hemoglobin, which can cause acute kidney injury that leads to kidney failure and the need for long-term hemodialysis.
While several drugs have been tested to prevent kidney problems after surgery, this is the first one that actually worked.
"We tested whether administration of nitric oxide, a gas normally produced by cells in the lining of blood vessels, might render hemoglobin 'inert,' thereby decreasing the risk of both acute and chronic kidney injury," lead study author Lorenzo Berra, medical director of respiratory care at Massachusetts General Hospital in Boston and an assistant professor at Harvard Medical School, said in a press release.
Researchers studied 244 adults in Xi'an, China, who had surgery to replace more than one heart valve. The lengthy procedure required patients to be placed on cardiopulmonary bypass, a heart-lung machine, for at least 90 minutes.
The authors found that patients who received 80 parts per million of nitric oxide during and for 24 hours after surgery were less likely to develop acute kidney injury. Their chances decreased from 64 percent in the placebo-treated patients to 50 percent in those who received nitric oxide.
The risk for progressing to Stage 3 Chronic Kidney Disease reduced in 90 days, with a decrease from 33 percent in the placebo-treated patients to 21 percent in those who received nitric oxide. After one year, 31 percent in the placebo group had serious kidney disease compared to 18 percent in the nitric oxide group.
There was also a decrease in the overall mortality rate after one year, from 6 percent in the placebo group to 3 percent in the nitric oxide group. But because of the relatively small number of patients included in the study, this decrease did not reach statistical significance, researchers wrote.
And nitric oxide also appears to be safe, they wrote, because it did not have to be reduced or stopped in any of the patients who received the gas.
While the results are promising, the researchers say the study results may not be generalizable to all cardiopulmonary bypass patients. In the Chinese study, the patients all underwent the same type of surgery because their heart valve problems were caused by rheumatic fever. Most of the patients were young with an average age of 48.
In North America and Europe, degenerative heart disease is a more common cause of valve dysfunction, and older patients are more likely to have additional medical problems.
The researchers are now conducting a similar trial at the Massachusetts General Hospital to determine whether nitric oxide provides similar benefits as those seen in the Chinese study.
"We believe that the older patients with an increased number of cardiovascular risk factors, including obesity, hypertension and diabetes, may derive even greater benefit from nitric oxide administration during and after heart surgery," Berra said in comparison to the younger patients in the study in China.