Postoperative hypoxia is a contributory factor to cognitive impairment after cardiac surgery.

OBJECTIVE: Cognitive dysfunction and postoperative hypoxia are common sequelae of coronary artery bypass grafting, but there has been no study to determine whether there is any relationship between them. METHODS: Arterial blood gas measurements were performed before surgical intervention and on the second and fifth postoperative day, and neuropsychological assessments were performed before surgical intervention and 5 days and 3 months postoperatively by using a battery of 10 psychometric tests in 175 patients undergoing coronary artery bypass grafting. An estimate of overall performance on the battery at each assessment point was provided by a simple aggregate cognitive index score calculated from the mean z scores of 4 normally distributed test variables. Multiple regression analysis was performed by using the cognitive index score at day 5 as the dependent variable, with age, sex, duration of the operation, presence or absence of cardiopulmonary bypass, preoperative cognitive index score, and arterial oxygenation and percentage of saturation at day 5 as independent variables. RESULTS: The mean cognitive index score decreased significantly in 115 (66%) patients who agreed to neuropsychological test battery assessment on the fifth postoperative day but improved significantly beyond baseline at 3 months. Mean arterial oxygen tension and percentage of saturation decreased significantly 2 days after the operation and, although improving over the following 3 days, remained decreased at day 5. Decreased cognitive index scores at day 5 strongly predicted cognitive impairment at 3 months (r = 0.36). The only significant independent predictors of the day 5 cognitive index score in the multiple regression analysis were preoperative cognitive index score and arterial oxygenation tension at day 5 (r = 0.24, P <.03). CONCLUSIONS: We report a significant correlation between postoperative cognitive dysfunction and hypoxia 5 days after coronary artery bypass grafting. This finding might have therapeutic implications because early postoperative cognitive dysfunction influences long-term impairment.

Neuroprotection during cardiac surgery: a randomised trial of a platelet activating factor antagonist.

OBJECTIVE: To assess platelet activating factor (PAF) antagonists, potent neuroprotective agents in experimental cerebral dysfunction, in clinical practice. DESIGN: Double blind, minimised, placebo controlled trial of low and high dose PAF antagonist (lexipafant). SETTING: Cardiac surgery unit. PATIENTS: 150 patients undergoing coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass. INTERVENTIONS: Randomisation to placebo, low dose (10 mg) or high dose (100 mg) lexipafant. MAIN OUTCOME MEASURES: Incidence of impairment on four established cognitive tests, undertaken before, five days, and three months after CABG, examined by three methods for defining impairment. RESULTS: The three groups were similar with respect to preoperative and intraoperative factors. Observed levels of cognitive impairment were less than had been predicted from previous studies. There was no difference in the groups in cognitive change scores at five days or three months. Group mean analysis showed significant time factors for all four tests but not for interactions or for the lexipafant group. A composite cognitive index, based on the aggregate of four normally distributed tests, showed a significant effect for timing of the test but not for the lexipafant group or interaction. Age, but not duration of bypass, was the most important determinant of postoperative cognitive impairment. CONCLUSIONS: The neuroprotective PAF antagonist lexipafant did not differentially reduce the level of cognitive impairment after CABG as determined by power estimates derived from published studies. The strongest predictors of cognitive impairment were age and timing of the test after operation.

Is cardiopulmonary bypass still the cause of cognitive dysfunction after cardiac operations?

OBJECTIVE: The purpose of this study was to determine whether cognitive impairment is related to cardiopulmonary bypass. METHODS: Twenty-five patients undergoing coronary artery bypass grafting without cardiopulmonary bypass were matched with 50 patients undergoing coronary artery bypass grafting with cardiopulmonary bypass. All patients received the same anesthetic regimen, and one surgeon performed all the operations. A battery of 10 standard tests of neuropsychologic function were performed before, at discharge, and 3 months after the operation. A comprehensive multidimensional measure of subjective health status was used as the primary clinical measure of functional outcome. RESULTS: The groups were similar with respect to age, sex, and ventricular function and differed only in the need for a circumflex artery graft. Both groups showed significant improvement in the comprehensive multidimensional measure of subjective health status at 3 months. At discharge most neuropsychologic tests had deteriorated in both groups (the same 4 tests had deteriorated significantly in both groups, and an additional test had deteriorated significantly in the cardiopulmonary bypass group). At 3 months all but one test in the cardiopulmonary bypass group had returned to or exceeded baseline performance. The same 2 tests had improved significantly in both groups, and a further test had improved significantly in the group without cardiopulmonary bypass. At no specific time point was there a significant difference between the absolute or change scores between the groups on any of the tests. CONCLUSIONS: The similar pattern of early decline and late recovery of cognitive function in patients undergoing coronary artery bypass grafting with and without cardiopulmonary bypass suggests that cardiopulmonary bypass is not the major cause of postoperative cognitive impairment. This merits consideration in deciding optimal treatment strategies in coronary revascularization.

Cognitive performance after cardiac operation: implications of regression toward the mean.

OBJECTIVE: The purpose of this study was to assess the influence of regression toward the mean on different definitions of cognitive dysfunction after coronary artery bypass graft operation. METHODS: A total of 120 patients who underwent nonemergency coronary bypass operation and who were involved in a randomized trial of an anti-inflammatory agent were assessed prospectively with a battery of 10 psychometric tests covering a variety of cognitive domains. The battery was administered before the operation and 5 days and 3 months after the operation. Data from 2 representative tests, the Rey Auditory Verbal Learning Test and the Trail Making Test (part A), were used. The influence of regression toward the mean on 3 commonly used single-case definitions of cognitive impairment (1 SD method; one-half SD method; 20% method) was analyzed. RESULTS: Group mean performance deteriorated on the Rey Auditory Verbal Learning Test at the discharge assessment (P <.001) and remained below baseline at 3 months (P =.03). Mean performance on the Trail Making Test (part A) showed a near-significant decline at discharge (P =. 06), followed by improvement at 3 months (P <.01). Regression toward the mean was demonstrated on both tests by classifying the preoperative scores into low, moderate, and high-performance categories. Applying the different definitions of dysfunction resulted in substantially larger numbers of patients in the high-performance group being classified as impaired. CONCLUSION: Single-case definitions of cognitive dysfunction are influenced strongly by regression toward the mean. Disproportionate numbers of high-baseline performers are classified as impaired, thereby questioning the validity of established definitions. Group mean analysis with controls is potentially the most reliable method for detecting real change or differences.