There are risks and benefits to using the heart-lung machine...or not.
Bypass surgery, an operation to reroute blood around blocked arteries in the heart, was made possible in part by the development of the heart-lung machine, which doctors call a "pump." This machine circulates and oxygenates blood during the procedure, allowing a surgeon to perform the delicate operation on a heart that is empty of blood and lying still.
Although bypass surgery successfully restores blood flow to the heart, some people emerge from the operation with memory loss or foggy thought processes (called cognitive dysfunction). These complications, which doctors privately call "pump head," were initially attributed to the use of the heart-lung machine.
Technology makes off‑pump surgery possible
The technological advances that have made surgery on a beating heart possible include instruments that stabilize the heart, shunts that re-route blood away from the surgical field while permitting the heart to continue pumping blood, and instruments that limit motion only in the area of the heart being operated on.
In an effort to avoid such complications, surgeons in the late 1990s devised a method of performing bypass surgery without a heart-lung machine, or "off pump." It was expected to become the new standard of care, yet in 2011, only 23% of bypass operations in the United States were performed off pump.
Is off-pump bypass surgery better or safer than bypass surgery done with a heart-lung machine? Studies aimed at determining whether one approach might be superior to the other have not produced a winner, but they have reinforced the idea that there are advantages to both.
Off-pump bypass surgery
In off-pump bypass surgery, a stabilizer immobilizes the part of the heart with the diseased coronary artery. The surgeon performs the bypass graft while the rest of the heart continues to beat and pump blood around the body.
Safer for high-risk cases
Most surgeons agree that individuals who are at greatest risk for complications from the heart-lung machine are the most likely to benefit from having bypass surgery performed off pump.
People who have suffered a stroke, or who have extensive cholesterol-filled deposits in their aorta (the large artery that carries blood out of the heart), are at increased risk for problems with their blood and other issues associated with use of the heart-lung machine. Those who are very elderly or have lung disease or poor kidney function are also vulnerable. Off-pump surgery makes bypass surgery possible for these people, because without this option, the risk of causing harm could outweigh the benefits of improving blood flow to the heart.
Conventional bypass surgery
In on-pump bypass surgery, oxygen-depleted blood flows from the veins into a sophisticated machine (below) that adds oxygen, filters and warms the blood, and pumps it back into the aorta and throughout the body. The heart is clamped off, so the surgery can be performed on a heart that is bloodless and lying still.
Surgeons have opinions
Surgeons have differing views on the use of off-pump surgery.
"My philosophy is that if the person is not at increased risk, there's no reason to do off-pump surgery. Yet if there's any chance that using the heart-lung machine might cause damage to the brain, lungs, or internal organs, I do not hesitate to operate off-pump," says Dr. Kamal Khabbaz, chief of cardiac surgery at Harvard-affiliated Beth Israel Deaconess Medical Center, who has experience in both approaches.
At one time Dr. Khabbaz performed off-pump surgery in most cases, but he now uses the approach only when he feels he must.
Taking an alternative view, Dr. John Byrne, the incoming chief of cardiac surgery at Harvard-affiliated Brigham and Women's Hospital, is a vocal fan of off-pump surgery. At Vanderbilt University Medical Center, where he has performed heart surgery since 2004, virtually all bypass operations are done off-pump.
"I think it's a better operation. There is less bleeding, fewer blood transfusions, less time on the ventilator, and patients recover faster," he says.
He agrees that off-pump surgery is mandatory for high-risk individuals, and explains that this is one reason he believes that any surgeon who does off-pump surgery should perform nearly every bypass operation off-pump.
"Any capable heart surgeon can do it, but to become proficient, you have to be committed to it and do hundreds of off-pump procedures. That's not possible operating on high-risk patients alone," he says.
What about "pump head"?
Several studies conducted over the last decade have found that memory loss and thinking problems following bypass surgery can occur when the operation is performed on-pump as well as off-pump. This means the heart-lung machine is likely not responsible. The culprit has not been identified, but there are many suspects. "It could be the result of trauma from the surgery, anesthesia, or pain medications," Dr. Khabbaz suggests.
The good news is that cognitive function gradually improves and generally returns to normal by 12 months.
More than 145,000 bypass operations are performed in the United States each year. Although some studies have determined that off-pump surgery does not result in fewer complications or longer-lasting results, as were expected, it's comparable to on-pump surgery and superior in higher-risk individuals. Both procedures are remarkably safe when performed by an experienced surgeon backed by a skilled team. In 2011, the operative mortality rate (death within 30 days of surgery) was 1.7% for on-pump bypass surgery and 1.8% for off-pump surgery.
So with this knowledge, how should people choose between these options or find a surgeon who performs surgery off-pump? Dr. Byrne suggests leaving the decision to those who know best.
"Find a good cardiologist who refers to a good surgeon. The surgeon is the captain of the ship and will choose whether an operation should be performed on- or off-pump," he advises.