July 18, 2005 — Since the beginning of modern medicine, doctors who administer anesthesia have largely confined their worries to the period beginning when patients are sedated and ending when they're fully awakened.
Now, two startling studies suggest that the effects of anesthesia linger for a year or longer, increasing the risk of death long after the surgery is over and the obvious wounds have healed.
"We don't know whether the things we do really have an effect that lasts a very long period of time, but there is enough evidence to suggest it might," says Dr. David Gaba, a professor of anesthesiology at Stanford University School of Medicine. "Even if it's a subtle and fairly uncommon phenomenon, it could affect an awful lot of people."
About 20 million Americans undergo surgery with general anesthesia each year.
Worries about the long-term effect of anesthesia -- and the demands for additional studies -- began to emerge recently when two research groups published papers linking deep sedation and an increased risk of death in the year or two after surgery.
One study, presented last fall at the American Society of Anesthesiologists annual meeting by Swedish researchers, showed that the duration spent under deep anesthesia was a significant risk factor for predicting death up to two years after surgery. Although the patients in the study were undergoing noncardiac surgery, most deaths resulted from heart attacks or cancer.
The other study, published in the journal Anesthesia & Analgesia in January by Duke University researchers, found that longer amounts of time spent under deep sedation increased the risk of death in the year following surgery. The patients in the Duke study underwent major, noncardiac surgery with general anesthesia, and again, deaths in the first year after surgery were primarily from heart attacks or cancer.
Some experts suggest that anesthesia and surgery may ignite a cascade of inflammation in the body that can aggravate heart, respiratory, cancer conditions or dementia.
According to the leading theory, surgery and anesthesia trigger the release of stress hormones, such as norepinephrine, that in turn activate inflammatory responses in the body and undermine the workings of the immune system. Inflammation is known to worsen many diseases, including heart disease, cancer, even dementia.
Since the first studies were published, newer research has suggested that noncardiac surgery with anesthesia also can cause a cognitive decline in some elderly people up to two years after the surgery, says Dr. Terri Monk, a professor of anesthesiology at Duke who led the study.
"Neither surgery nor anesthesia is a natural thing," Gaba says. "What some people suspect -- but there is still not much evidence for -- is there could be people whose inflammation processes don't come back to normal after surgery but stay revved up for a very long time."