Cognitive function after coronary bypass surgery: effect of decreased cerebral blood flow

The First Cardiac Anesthesiology Fellow, William A. Lell: A Brief History

Fifty years ago, on August 1, 1971, William A. Lell became the first cardiac anesthesia fellow at Harvard's Massachusetts General Hospital (MGH) Department of Anesthesiology, training with the world's first group of anesthesiologists whose clinical practice, teaching, and research efforts were exclusively devoted to cardiac anesthesia. Lell's early interest in cardiovascular medicine and how mentors, particularly at the MGH, influenced his early career development are recounted. The challenges a young pioneer faced in establishing and maintaining an academic cardiac anesthesia program during the initial and rapid growth of an exciting new subspecialty are described. Dr Lell's experience emphasizes the importance of seizing new opportunities and establishing meaningful working relationships with colleagues based on mutual trust as fundamental to successful career development and research in a new medical subspecialty.

Toward Understanding Cerebral Blood Flow during Cardiopulmonary Bypass: Implications for the Central Nervous System

Factors and Their Influence on Regional Cerebral Blood Flow during Nonpulsatile Cardiopulmonary Bypass. By Govier AV, Reves JG, McKay RD, Karp RB, Zorn GL, Morawetz RB, Smith LR, Adams M, and Freeman AM. Ann Thorac Surg. 1984; 38:609-13. Reprinted with permission.In this study, we examined the relationship of regional cerebral blood flow (CBF) to mean arterial pressure, systemic blood flow, partial pressure of arterial carbon dioxide (PaCO2), nasopharyngeal temperature, and hemoglobin during hypothermic nonpulsatile cardiopulmonary bypass (CPB). Regional CBF was determined by clearance of xenon 133 in 67 patients undergoing coronary bypass grafting procedures. There was a significant decrease in regional CBF (55% decrease) during CPB, with nasopharyngeal temperature and PaCO2 being the only two significant factors (p < 0.05). In a subgroup of 10 patients, variation of pump flow between 1.0 and 2.0 L/min/m2 did not significantly affect regional CBF. We conclude that cerebral autoregulation is retained during hypothermic CPB. Under the usual conditions of CPB, variations in flow and pressure are not associated with important physiologic or detrimental clinical effects.

Interpreting studies of cognitive function following cardiac surgery: a guide for surgical teams

Patients with coronary disease and related health care providers are faced with confusing and often conflicting information with regards to the neurocognitive impact of different strategies for coronary revascularization. Studies involving the measurement of postoperative cognitive deficit (POCD) have significant limitations that may ultimately impact on their interpretation and clinical relevance. In this review, we have described the origin of these tests and delineated the rationale for the design of testing that is commonly used in cardiac surgery patients. In general, neurocognitive tests assess domains of memory/new learning, psychomotor speed/dexterity and attentional capacity/mental control. Pre- and post-intervention tests in each domain can be evaluated either by the measurement of mean change scores (Group Comparison Model) for the entire group as continuous data, or by using categorical or continuous data to examine patterns of individual decline (Individual Comparison Model). This latter approach requires a specific definition of what constitutes a decline, which can be criticized as being arbitrary. There are limitations to each of these approaches that necessitate that critical information in trial design is available to the reviewer to facilitate interpretation. For example, the impact of factors such as test/re-test reliability and practice effect can be mitigated by the use of an appropriately chosen control population. Liberal parlance of neurocognitive outcome as a rationale for therapeutic choice must be tempered by wise interpretation of these tests. It is only through the understanding of their limitations and the implications of trial design that we can translate these results to provide the best therapeutic options for our patients in unbiased manner.

The assessment of postoperative cognitive function

Postoperative cognitive function (POCD) has been subject to extensive research. In the literature, large differences are apparent in methodology such as the test batteries, the interval between sessions, the endpoints to be analysed, statistical methods, and how neuropsychological deficits are defined. Traditionally, intelligence tests or tests developed for clinical neuropsychology have been used. The tests for detecting POCD should be based on well-described sensitivity and suitability in relation to surgical patients. In tests using scores, floor/ceiling effects may compromise the evaluation if the tests are either too easy or to difficult. Uncontrolled testing facilities and change of test personnel may affect the test performance. Practice effects are pronounced in neuropsychological tests but have generally been ignored. The use of a suitable normative population is essential to allow correction for practice effects and variability between sessions. Missing follow-up may severely compromise valid conclusions since subjects unable or unwilling to be examined are particularly prone to suffer from POCD. In the statistical analysis of the test results, the evaluation should be based on differences between pre- and postoperative performance. Parametric statistical tests are not relevant unless the appropriate Gaussian distributions are present, perhaps after transformation of data. The definition of cognitive dysfunction should be restrictive and the criteria should be fulfilled in only a small proportion of volunteers. In the literature, these requirements often have not been fulfilled. This precludes a reasonable estimation of the incidence of POCD and the conclusions of comparative studies should be interpreted with great caution. In this review article, we present a number of recommendations for the design and execution of studies within this area. In addition, the critical reader may use these recommendations in the evaluation of the literature.

Neuropsychologic dysfunction after cardiac surgery: what is the problem?

Twenty years ago Aberg published his seminal studies on the neuropsychologic consequences of cardiopulmonary bypass (CPB). Twenty years later, what is the state of current research on the problem of post-CPB neurologic injury, and what different management techniques have been employed to influence this outcome? This article reviews the definition and assessment of postoperative neuropsychologic dysfunction; epidemiologic data and associated risk factors assessing post-CPB neuropsychologic dysfunction are critically appraised.

Analysis and interpretation of neuropsychologic tests in cardiac surgery

Neuropsychologic assessment in the context of cardiac surgery is constrained by the clinical time available to see patients, and as such test selection needs to be carefully planned. Besides the time limitations, it differs from clinical neuropsychologic assessment primarily because it tends to involve at least two assessments, a comparison with performance before operation, and a limited number of tests. The analysis and design issues involved in both incidence studies and intervention studies are discussed in this article. Incidence studies customarily involve a single group assessed on at least two occasions and are designed to identify the numbers of individuals who show clear evidence of neuropsychologic changes after a cardiac operation. Intervention studies involve at least two groups where one factor (eg, surgical equipment) is varied systematically. The research on neuropsychologic deficits after cardiac operations has progressed from incidence studies, which involve a conventional definition of deficit, to intervention studies, in which specific test performance can be compared.