Neurocognitive outcomes: the year in review

This review is a survey of the recent literature investigating the etiology and the relative incidence of postoperative neurological and cognitive dysfunction after cardiac surgery.

Several studies reviewed here have employed transcranial Doppler for detection of cerebral emboli and compared results between patients undergoing beating-heart versus conventional cardiopulmonary bypass. A transcranial Doppler device ostensibly discriminating between particulate and gaseous emboli has additionally been employed, yet despite a consistently lower incidence of cerebral emboli associated with avoidance of cardiopulmonary bypass, several groups have reported similar incidences of cognitive dysfunction across these procedures, suggesting other, potentially more important, factors. Two recent studies have focused on the hazards associated with perioperative anemia in both infants and older patients, and which can result in developmental delay or profound changes in cerebral blood flow. A further study has identified an adverse interaction with postoperative hypoxia. The use of intraortic filtration for capture and removal of particulate macroemboli has been associated with a reduction in the incidence of clinically apparent central-nervous-system injury and should be further investigated. Several other studies identify pre-existing levels of central-nervous-system impairment prior to surgery, underscoring the confounding issues introduced by the failure to include a non-surgical comparator group.

While further evidence of cerebral embolization continues to accrue, several studies suggest that other factors may be of equal or greater importance in cognitive dysfunction. Further investigations into the role of perioperative anemia, co-incident hypoxemia and other aspects of perioperative care, e.g. hyperglycemia and postoperative hyperthermia, are warranted.