Health risks continue well after surgery
by Toni Baker
Even successful surgery heightens the risk of cardiovascular disease and possibly cancer for weeks or even years, say MCG physician-scientists studying the unintended effects of surgery.
“When bad things happen down the road we cannot, as we have in the past, just attribute it to the natural course of illness,” said Dr. Steffen E. Meiler, anesthesiologist and vice chair for research in the Department of Anesthesiology and Perioperative Medicine. “We have to start taking responsibility for some of it, certainly not all of it.”
That requires more basic science and human studies to understand the mechanisms underlying ill effects and a concerted effort to avoid them, said Dr. Meiler. He discussed this topic at the 53rd Annual Meeting of the Japanese Society of Anesthesiologists June 1-3 and as guest editor of the June issue of Anesthesiology Clinics of North America devoted to the matter.
A few studies have been done across the broad spectrum of the topic, including whether short-term surgical complications, such as infections or pulmonary problems, predict long-term complications and whether mutations in genes involved in inflammation increase stroke risk after cardiopulmonary bypass surgery.
Mounting evidence suggests short- and long-term increased risks, particularly for surgery patients with serious underlying disease, said Dr. Meiler.
A key factor is how surgery affects the immune response.
“The inflammatory response to surgery, for the most part, is a very good thing. We need it to protect ourselves against infection,” he explained. “We need it to heal the surgical wound properly. But if you are in a high-risk group, if you are not generally healthy except for your specific surgical indication, that protective inflammatory process may also stir up trouble.”
Inflammation is a player in most major diseases, including cardiovascular disease and cancer. For example, the chronic inflammation of heart disease may be exacerbated by bypass surgery. “It’s like stepping on the gas pedal,” said Dr. Meiler.
Studies have shown that drugs such as statins, beta blockers and clonidine can protect against some of this risk.
Even body temperature is a factor. “We now have solid evidence that if patients drop their core temperatures during surgery below 36 degrees Celsius (96.8 degrees Fahrenheit), the complication rate from postoperative infections for certain surgical procedures may be as high as threefold.”
Infections and even cancer are concerns postsurgically as lower body temperature, blood transfusions and apparently volatile anesthetics actually suppress the immune response.
Still, this is one of many issues related to surgical effects that need more exploration. “I can’t tell you that volatile anesthetics definitely have a contributory effect, only that animal models would suggest they do,” Dr. Meiler said.
His research is showing the impact of even a small infection in the face of chronic inflammation. Using an animal model of sickle cell disease, a disease marked by systemic inflammation, he is studying the host’s defense to microbial products such as lipopolysaccharide.
He has found that macrophages, which typically work like garbage collectors for the immune system, transform into large, pro-inflammatory cytokine-spewing cells. “Macrophages residing in areas of sickle cell-induced tissue injury become large, express different receptors on their surface and, when exposed to a superimposed infectious stimulus like lipopolysaccharide, respond with an overwhelming release of pro-inflammatory cytokines that are harmful to the host.”
The mice die rapidly and these re-programmed macrophages may help explain why children with sickle cell disease are more prone to overwhelming and potentially deadly infections following surgery.
“We need more investigations, more data on humans,” said Dr. Meiler, noting that while short-term outcomes of inflammation in response to surgery are well established, proof of longer-term outcomes will take more work.
In the meantime, patients can benefit from early, ongoing collaboration by all members of the health care team to ensure risk reduction through steps such as minimizing surgical incisions, avoiding transfusions when possible and, when indicated, pharmacological treatment before surgery to help reduce cardiovascular complications.
“The challenge will be to incorporate these measures consistently across the health care process so that all eligible patients benefit from these insights,” Dr. Meiler said.