Patients who are considering cardiopulmonary bypass (CPB) surgery can now add to their list of worries the possibility that the procedure causes lasting cognitive impairment.
Concerns about the aftereffects of CPB have existed since it was first introduced more than 40 years ago, but statistically reliable evidence of impairment has been limited. Now, a study published in Neuropsychology (Vol. 16, No. 3) shows that deficits in memory and attention can last as long as a month after surgery.
The study, conducted by Julian R. Keith, PhD, and colleagues at the University of North Carolina at Wilmington, compared the performance of patients on cognitive tests before and after CPB to the performance of healthy control participants. The researchers found that the procedure had no effect on reaction times, fine motor skills, visuospatial memory or verbal paired-associate memory, but it significantly impaired visual attention and auditory working memory.
Patients' performance did not actually decline after surgery on any of the measures. Instead, the finding of impairment was based on their failure to improve as much as controls between the first and second testing sessions. The result could explain why studies that lack control groups and use less sophisticated statistics have failed to detect impairments after the first few weeks.
Exactly why the patients were impaired remains unclear. CPB can expose patients' brains to inflammation, cold, anoxia and showers of small blot clots, but establishing which of these factors is responsible has proven difficult. Nonetheless, the study provides strong evidence that patients who undergo CPB suffer lasting cognitive impairment, and it could serve as a wake-up call to those who have dismissed previous findings, says Keith.
"Bypass surgeons have been looking at the studies and dismissing them, saying, 'These studies are flawed and I'm not going to pay any attention to them,'" he explains. "Now we can get researchers to pay more attention to coming up with ways to protect patients during surgery."
The study could also encourage clinicians to test for impairments after CPB and to help patients cope with any deficits that are discovered, says Keith.
"Everybody thinks about physical rehab, but nobody considers the need for psychological or cognitive rehab," he adds. "What I would love to see is for the surgeons and cardiologists to be referring patients to a neuropsychologist for neuropsychological rehabilitation in the same way that they refer them to specialists for physical rehabilitation."