Differential age effects of mean arterial pressure and rewarming on cognitive dysfunction after cardiac surgery.

Central nervous system dysfunction is a common consequence of otherwise uncomplicated cardiac surgery. Many mechanisms have been postulated for the cognitive dysfunction that is part of these neurologic sequelae. The purpose of our investigation was to evaluate the effects of mean arterial pressure (MAP) during cardiopulmonary bypass (CPB) and the rate of rewarming on cognitive decline after cardiac surgery. Two hundred thirty-seven patients completed preoperative and predischarge neuropsychologic testing. MAP and temperature were recorded at 1-min intervals using an automated anesthesia record keeper. MAP area less than 50 mm Hg (time and degree of hypotension), as well as the maximal rewarming rate, were determined for each patient. Multivariable linear regression revealed that the rate of rewarming and MAP were unrelated to cognitive decline. However, interactions significantly associated with cognitive decline were found between age and MAP area less than 50 mm Hg on one measure, and between age and rewarming rate in another, identifying susceptibility of the elderly to these factors. Although MAP and rewarming were not the primary determinates of cognitive decline in this surgical population, hypotension and rapid rewarming contributed significantly to cognitive dysfunction in the elderly.

Effect of aging on cerebral autoregulation during cardiopulmonary bypass. Association with postoperative cognitive dysfunction.

BACKGROUND: Age is a predictor of cognitive dysfunction after cardiac surgery, but the mechanism is unknown. The purpose of our study was to determine whether age-related decrements in cognition are associated with cerebral blood flow (CBF) autoregulation during cardiopulmonary bypass (CPB). METHODS AND RESULTS: Cognitive function testing was completed before surgery and before hospital discharge in 215 patients undergoing elective coronary artery bypass grafting (CABG) surgery. The battery consisted of seven tests with nine measures designed to evaluate memory, mood changes, and visuomotor speed and function. Pressure-flow and metabolic-flow cerebral autoregulation during hypothermic cardiopulmonary bypass were determined using the 133Xe clearance CBF method and radial artery and jugular bulb effluent to calculate cerebral metabolic rate (CMRO2) and cerebral AV difference (C[AV]O2). Pressure-flow autoregulation was tested by using two CBF measurements at stable hypothermia: one at stable mean arterial pressure (MAP) and the second 15 minutes later when MAP had increased or decreased > or = 20%. Metabolism-flow autoregulation was tested by varying the temperature (CMRO2) and measuring the coupling of CBF and CMRO2. Individual patient autoregulation was correlated with changes in cognitive measures. Cognitive performance declined in 6 of 9 measures after CABG surgery. Age predicted cognitive decline in 7 of 9 measures; short-term memory showed the greatest effect of age. Pressure-flow autoregulation during hypothermic CPB showed a small but significant (P < .0001) effect of pressure on CBF. There was no effect of age on the slope of CBF response to changes in MAP (pressure-flow autoregulation). There was a major effect of temperature on CBF during CPB (P < .0001). Coupling CBF and CMRO2 with changing temperature was unaffected by age. Changes in cognition were not associated with measures of cerebral autoregulation. However, increasing C(AV)O2 is associated with cognitive deficits in 5 of 9 measures; these associations were independent of age. CONCLUSIONS: Increased age predisposes to impaired cognition after cardiac surgery. This decline in cognitive function in the elderly is not associated with age-related changes in cerebral blood flow autoregulation. The association of increased oxygen extraction with decline in some measures of cognitive function suggests that an imbalance in cerebral tissue oxygen supply, which is unrelated to age, contributes to acute cognitive dysfunction after cardiac surgery. Cognitive dysfunction after CPB in the elderly cannot be explained by impaired CBF autoregulation.