Neurocognitive Outcomes of Cardiac Surgery

Abstract

SINCE THE EARLY PERIOD of modern cardiac surgery, it has been recognized that some patients experience severe neurologic complications due to cerebral ischemic injury. Additionally, autopsy studies of patients who died shortly after cardiac surgery due to cardiovascular causes without apparent neurologic deficits exhibited cerebral ischemic lesions. The authors proposed that mild cerebral ischemic injuries also may exist in surgical survivors who exhibit no apparent neurologic deficits or only transient neurologic disturbance. Now, it is understood that there is a range of neurologic complications following cardiac surgery, and they are classified by the American College of Cardiology/American Heart Association into 2 types: type 1 consists of major focal neurologic deficits, stupor, and coma; type 2 consists of milder, more diffuse deficits without evidence of focal injury, including delirium and deterioration of cognitive function. Starting in the 1980s, researchers began using neuropsychological testing to assess milder forms of neurologic deficits following cardiac surgery and found that many patients exhibited declines in neurocognitive test performance. Postoperative cognitive decline (POCD), also referred to as ‘‘postoperative cognitive dysfunction’’ and ‘‘postoperative cognitive deficit’’, has been presumed to reflect a disturbance of brain function that is related causally to surgery. Despite many years of study demonstrating the association of cardiac surgery with neurocognitive decline, the underlying mechanisms that implicate causation remain unclear. It is a reasonable hypothesis that mild cerebral ischemia due to microembolization or hypoperfusion or both causes POCD, but direct causation has not been demonstrated. This lack of clarity, at least partially, is attributable to varying neurocognitive outcomes research methods. With the aim of increasing methodologic consistency, a multidisciplinary group of experts led by John Murkin published a consensus statement in 1995 that recommended a core battery of neuropsychologic tests. In 1997, they further proposed a means of analyzing test