Every year, about half a million Americans undergo open-heart surgery. Roughly 60 percent of them experience some degree of mental decline after the surgery, a phenomenon that surgeons call "pumphead." A new study in this month's Annals of Thoracic Surgery sheds light on possible causes of the mysterious condition, which in some patients is temporary but in others may last a lifetime.
"It has been well-documented that there is an issue of cognitive decline in the period of time [a few months] immediately after surgery," says lead study author James Slater, a cardiothoracic surgeon at Atlantic Health System in Morristown, N.J. Slater says the amount of cognitive decline varies; some patients have a tough time concentrating, others have trouble with memory and learning. Slater recalls, for instance, a onetime crossword whiz who, post-surgery, could no longer do The New York Times Sunday crossword puzzle. (Read about Bruce Stutz's experience with "pumphead" in the June 2003 issue of Scientific American.)
Once believed to be a passing phase, researchers have found that pumphead may linger indefinitely – or return years after an operation and persist. A 2001 study published in The New England Journal of Medicine found that 42 percent of patients suffered cognitive decline five years after receiving open-heart surgery (For some, the cognitive problems had continued or returned, while others were experiencing them for the first time).
The exact causes of pumphead are still up for debate, but Slater's research suggests it is at least partly due to problems with oxygen reaching the brain during surgery. In conventional open-heart surgery (most often performed to clear blocked vessels supplying blood to the heart), a patient is hooked up to a heart-lung machine for the duration of the three-or-so-hour procedure. The heart-lung machine takes over the job of the heart (which is stopped during the surgery), pumping oxygen-rich blood through the body. But the machine is not as efficient as the real heart when it comes to delivering a healthy supply of oxygen-rich blood to the brain, Slater says. And as his study shows, the resulting oxygen deprivation appears to be a major factor in pumphead.
Slater's team followed 240 patients that underwent open-heart surgery from 2004 to 2006. All of the patients were hooked up to cerebral oximonitor sensors that track the amount of oxygenated blood reaching the brain. The researchers found that patients whose oxygen levels fell below a certain threshold (calculated using a mathematical formula) had double the chance of suffering at least some cognitive decline. The study only followed up patients for three months after their operations, so it is not clear whether oxygen deprivation is related to cognitive decline years after the procedure.
Mark Newman, chair of anesthesiology at Duke University School of Medicine in Durham, N.C., says that another possible cause of pumphead is that fatty deposits that normally adhere to the walls of blood vessels may become dislodged and travel to the brain (and cause clots) when doctors clamp the vessels to hook patients up to a heart-lung machine. In addition, he says, "Some people are genetically more susceptible to pumphead than others. That could be related to immune response." Surgery can cause a big outpouring of immune system cytokines and white blood cells whose job is normally to fight foreign invaders such as viruses and bacteria but may get confused and mistakenly attack healthy tissue, Newman says.
The good news, Slater says, is that there already exists a technology that might help doctors avert the problem: a monitor (the same one used in his study) that tracks the amount of oxygen-rich blood reaching the brain during surgery, informing doctors when they should take steps to prevent brain damage—giving a patient meds to increase blood pressure and boost oxygen in the brain, for example. The device is already being used in some 700 U.S. hospitals.
(Update, posted 1/12/09: A commenter asked a good question, whether Slater had any financial interest in the oximeter he used in the study. The answer, Slater tells us, is no: "I have no financial interest in the company or the product," he wrote in an email. "The research was done funded with our own research funds. Absolutely no conflict of interest to declare.")
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