Neuropsychological dysfunction after cardiopulmonary bypass: a comparison of two institutions

Dynamic bubble trap can replace an arterial filter during cardiopulmonary bypass surgery

Objective: The arterial filter (AF) and the dynamic bubble trap (DBT) reduce the number of air microbubbles passing through these devices. The aim of the study was to confirm that the DBT diminishes microbubbles in the arterial line similar to, or better than, the AF, and can replace it.

Methods: In a clinical study, we evaluated 60 patients undergoing cardiopulmonary bypass surgery, divided into two groups (30 patients each). In the first group, we used an open extracorporeal system, and in the second group, a closed system. For 15 patients in each group, the AF was incorporated, the other 15 patients received the DBT. The microbubbles were counted before and after the AF or DBT, using two-channel-ultrasonic Doppler devices.

Results: The exposure of patients to small bubbles (<45μm) is significantly higher in the AF than in the DBT group. The DBT reduces large bubbles (<45μm) better than the AF, with a rate exceeding 16%.

Conclusion: The use of the DBT instead of the AF yields higher air micro-bubble removal efficacy, allowing replacement of the AF, assuming the AF is used for air removal purpose only.

Attempting to maintain normoglycemia during cardiopulmonary bypass with insulin may initiate post-operative hypoglycemia

Cardiopulmonary bypass is known to cause alterations in insulin secretion and resistance, resulting in profound hyperglycemia. Aggressive treatment of the resulting hyperglycemia intra-operatively could result in a severe degree of post-operative hypoglycemia. We undertook this prospective non-randomized clinical study to compare the alterations in glucose homeostasis in diabetic (group A, n=50) and non-diabetic (Group B, n=50) patients undergoing moderate hypothermic (30°C) cardiopulmonary bypass for coronary artery bypass grafting (CABG). All patients had a fasting blood sugar level done on the morning of surgery. Blood sugars were monitored intra-operatively and post-operatively at fixed time intervals. Intra-operative hyperglycemia was treated aggressively by a continuous, infusion of injecting plain insulin. Both the groups experienced similar significant increase in blood glucose levels during bypass ('p'=0.00003). However, the mean blood glucose level upon arrival in the intensive care unit was significantly decreased in group B compared to group A (p=0.0002). 60% of group B and 10% of group A patients required treatment for post-operative hypoglycemia (blood glucose level <60mg/dl). This clinical study reveals that attempting to maintain normoglycemia in this setting with Insulin may initiate post-operative hypoglycemia.

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.

Scanning electron microscopic analysis of arterial line filters used in cardiopulmonary bypass

The clinical value of arterial line filters is still a controversial issue. Proponents of arterial line filtration argue that filters remove particulate matter and undissolved gas from circulation while opponents argue the absence of conclusive clinical data. We conducted scanning electron microscope (SEM) studies of arterial line filters used clinically in the cardiopulmonary bypass circuits during adult cardiac surgery and analyzed the types and characteristics of materials entrapped in the arterial line filters. Twelve arterial line filters were obtained during routine hypothermic cardiopulmonary bypass in 12 adult cardiac patients. The arterial line filter was a screen type with a pore size of 40 microm (Baxter Health Care Corporation, Bentley Division, Irvine, CA, U.S.A. ). After opening the housing, the woven polyester strands were examined with SEM. All segments examined (120 segments, each 2.5 x 2. 5 cm) contained no embolic particles larger in their cross-sectional area than the pore size of the filter (40 microm). The origins of embolic particulates were mostly from environmental foreign bodies. This may suggest a possible need for more aggressive filtration of smaller particulates than is generally carried out at the present time.

Attempting to maintain normoglycemia during cardiopulmonary bypass with insulin may initiate postoperative hypoglycemia

We attempted to develop an insulin administration protocol that maintains normoglycemia in patients undergoing cardiac surgery and to study the effects of intraoperative blood glucose management on serum levels of creatine phosphokinase isoenzyme BB (CK-BB) and S-100 protein. Twenty nondiabetic patients were randomly allocated to receive either "tight control" of blood glucose with a standardized IV insulin infusion intraoperatively (Group TC) or "no control" of blood glucose intraoperatively (Group NC). Perioperative serum levels of glucose, CK-BB, and S-100 protein were determined in all patients. Group TC patients received 90.0 +/- 49.2 units of insulin, whereas Group NC patients received none. Despite insulin, both Group TC (P = 0.00026) and Group NC (P = 0.00003) experienced similar significant increases in blood glucose levels during hypothermic cardiopulmonary bypass. However, mean blood glucose level upon intensive care unit arrival was significantly decreased in Group TC, compared with Group NC (84.7 +/- 41.0 mg/dL, range 32-137 mg/dL vs 201.4 +/- 67.5 mg/dL, range 82-277 mg/dL, respectively; P = 0.0002). Forty percent of Group TC patients required treatment for postoperative hypoglycemia (blood glucose level <60 mg/dL). Substantial interindividual variability existed in regard to insulin resistance. The investigation was terminated after we realized that normoglycemia was unattainable with the study protocol and that postoperative hypoglycemia was unpredictable. All patients in both groups experienced similar significant increases in postoperative serum levels of CK-BB and S-100 protein. These results indicate that "tight control" of intraoperative blood glucose in nondiabetic patients undergoing cardiac surgery was unattainable with the study protocol and may initiate postoperative hypoglycemia.

IMPLICATIONS

The appropriate intraoperative management of hyperglycemia and whether it adversely affects neurologic outcome in patients after cardiac surgery remains controversial. This investigation reveals that attempting to maintain normoglycemia in this setting with insulin may initiate postoperative hypoglycemia.

Determinants of cognitive change after coronary artery bypass surgery: a multifactorial problem

BACKGROUND

Several studies have investigated predictors of cognitive decline after coronary artery bypass grafting (CABG), but there is little consensus as to which specific factors are predictive of poor cognitive outcomes.

METHODS

We evaluated 127 patients undergoing CABG with standardized neuropsychological tests preoperatively, at 1 month and at 1 year. The outcome measure was a continuous variable reflecting change in z-scores for eight cognitive domains over time for individual patients. Univariate analyses were performed to evaluate the association between the demographic, operative, and postoperative factors and the cognitive outcome variables. Factors that were significant were included in a multiple linear regression analysis.

RESULTS

Among the medical history variables, diabetes was associated with change in executive functions and psychomotor speed. Some of the operative variables were associated with short-term changes, but none with the 1-year outcomes. For example, the surgeon's rating of degree of difficulty in selecting a cross-clamp site was associated with change in attention. Higher mean pump rate during the procedure was associated with improved performance on tests of language. The cognitive domains associated with medical variables were different from those associated with surgical variables, and the associations observed at 1-year were different from those seen at 1-month.

CONCLUSIONS

Change in cognition after CABG is associated with both medical and surgical variables. The specifics of these associations depend on the choice of time points after surgery. This suggests that there are multiple etiologies for these changes, with nonspecific effects of anesthesia and prolonged surgery interacting with the more specific effects of the surgical procedure itself.

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.

Perfluorocarbon emulsions and cardiopulmonary bypass: a technique for the future

Artificial blood has been sought for a considerable period of time and two major lines of research have led to FDA testing of some possible compounds. The two major types of compounds are polymerized hemoglobin moieties and perfluorocarbon emulsions (PFC). Polymerized hemoglobin preparations have the ability to carry oxygen and release it in a manner similar to the oxyhemoglobin dissociation curve of whole blood. PFCs carry oxygen, nitrogen and carbon dioxide, as well as all other non-polar gases, by enhanced chemical solubility. Therefore, all dissolved gases are available for metabolic utilization and no sinusoidal release curve of oxygen is encountered. Early PFC emulsions had problems with toxicity of the emulsifier and were difficult to get into their emulsion for infusion. Furthermore they were very dilute in the active ingredient for gas transport. Today there are second generation PFCs becoming available that have a 40% concentration of the PFC and therefore the potential for gas transport is greatly increased. The PFC emulsions have a very small size, 0.1 microns, so the surface for gas exchange is massively increased as well as the potential increased for perfusion into areas of potentially sludged erythrocytes. Work with the PFCs has shown them now to be able to carry adequate oxygen to work as blood substitutes. They have shown protection from air embolism in a number of animal and end-organ models. What makes the PFCs unique is their ability to carry/absorb nitrogen and therefore protect from gas embolization. There are data in animal models showing significant cerebral protection in cardiopulmonary bypass models. The new PFCs should sometime in the not-too-distant future be tested in human bypass with assessments of neuropsychiatric dysfunction and stroke.

Adverse neurologic events: risks of intracardiac versus extracardiac surgery

Intracardiac operations such as valve replacements have typically carried a higher risk (4.2% to 13%) of overt central nervous system outcome, compared with coronary artery bypass grafting (CABG) procedures (0.6% to 5.2%). This is likely owing to the increased risk of macroembolization of air or particulate matter from the surgical field during intracardiac surgery. The periods of highest risk for emboli are during aortic cannulation and especially during release of aortic clamps and weaning from bypass. The number of embolic events measured with transcranial Doppler is significantly higher in patients undergoing valve surgery compared with coronary surgery, particularly during cardiac ejection and immediately after bypass. However, there is current evidence that neurologic risk is increasing in patients undergoing CABG owing to the tendency to operate on older patients with more severe aortic atherosclerosis and cerebrovascular disease. Patients having an intracardiac procedure combined with a CABG procedure may be at particularly high risk for adverse neurologic outcome. For all cardiac surgical patients, there is some cause for optimism in that risk may be minimized by improved assessment (e.g., intraoperative transesophageal or epiaortic echocardiographic scanning of the ascending aorta to identify patients at risk) and monitoring (e.g., detection of embolic phenomena, using transesophageal echocardiography or transcranial Doppler technology). Furthermore, in the future, development and testing of more ideal cerebroprotective drugs may allow amelioration of neurologic injury, either by pretreating all patients at risk, or possibly even by delaying treatment until after the suspected occurrence of an insult.

Methodological issues in the assessment of neuropsychologic function after cardiac surgery

This report reviews critical issues facing investigators interested in neuropsychologic sequelae after cardiac operations: (1) experimental design; (2) selective attrition; (3) selection of instruments; (4) moderating factors; (5) definitions of cognitive decline; (6) statistical analysis; and (7) clinical significance. Implications for further research in the area are discussed.

Clinical study of normothermic cardiopulmonary bypass in 100 patients with coronary artery disease

During normothermic cardiopulmonary bypass (CPB), the body temperature is maintained at 37 degrees C. Since 1987, it has been our standard practice to use normothermic CPB in our patients undergoing a cardiac operation, and our experience now consists of more than 3,000 consecutive patients. Myocardial protection is achieved through the combination of cold intermittent antegrade blood cardioplegia, no topical cooling, and a terminal "hot shot" of blood cardioplegia. We disagree with the stance of the Toronto group that normothermic CPB requires the administration of large volumes of cardioplegic and crystalloid solutions and the frequent use of phenylephrine hydrochloride to ensure a low systemic vascular resistance. To establish a routine technique of cold heartwarm body bypass, we conducted a clinical study in 100 consecutive patients with coronary artery disease. We found that the total cardioplegia volume needed in our patients was 1,946 +/- 257 mL, versus 4,700 +/- 1,900 mL in the Toronto study, and an additional crystalloid volume loading of 400 +/- 141 mL during CPB was needed in 26% of our patients, versus a total volume of 3,650 +/- 800 mL in the Toronto series. Phenylephrine (250 micrograms) was used in 16% of our patients, versus 88% of the patients in the Toronto study (mean dose, 1.3 mg). During normothermic CPB, the mean radial arterial pressure was 57.3 +/- 9.4 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive function after open-heart surgery: are postoperative neuropsychological deficits caused by cardiopulmonary bypass?

Despite the many technological developments in arterial perfusion and cardiac surgical procedures, open-heart surgery is still believed to pose a significant risk for cerebral injury. There are several potential causes of brain damage during open-heart surgery, including prolonged or severe arterial hypotension, as well as emboli emanating from the cardiopulmonary bypass circuit or the operative field. This article reviews the available neuropsychological studies of outcome following cardiac valve replacement and coronary artery bypass grafting. Because both procedures are life-saving operations, the research in this area has been quasi-experimental and fraught with methodological problems. Nonetheless, the findings converge to suggest that cognitive dysfunction occurs after open-heart surgery, and that the deficits are attributable, at least in part, to factors specific to the operation or to the patient being maintained on cardiopulmonary bypass. Preliminary findings suggest that embolization is the primary cause of perioperative deficits in uncomplicated operations. Studies have also consistently found preoperative deficits in this population, suggesting that neuropsychological dysfunction is caused by severe chronic cardiac disease as well as open-heart surgery.