Cerebral protection during open-heart surgery

Neuroprotective Effect of Low Mean Arterial Pressure on Postoperative Cognitive Deficit Attenuated by Prolonged Coronary Artery Bypass Time: A Meta-Analysis

Introduction

The true influence of the low mean arterial pressure (low MAP) during coronary artery bypass grafting (CABG) on the development of postoperative cognitive deficit (POCD) remains controversial. We aimed to perform a meta-analysis and meta-regression to determine the effect of low MAP on POCD, as well as moderator variables between low MAP and POCD.

Methods

The Web of Science, PubMed database, Scopus and the Cochrane Library database (up to June 2018) were searched and retrieved articles systematically reviewed. Only randomized controlled trials (RCTs) comparing maintenance of low MAP (<80 mmHg) and high MAP (>80 mmHg) during cardiopulmonary bypass (CPB) were included in our final review. Statistical analysis of the risk ratio (RR) and corresponding 95% confidence interval (CI) was used to report the overall effect. The overall effect and meta-regression analysis were done using Mantel-Haenszel risk ratio (MHRR) and the corresponding 95% confidence interval (CI).

Results

A total of 731 patients in three RCTs were included in this study. POCD occurred in 6.4% of all cases. Maintenance of low MAP did not reduce the occurrence of POCD (MHRR 1.012 [95% CI 0.277-3.688]; Z=0.018; P=0.986; I²=66%). Shorter CPB time reduced the occurrence of POCD regardless of group assignment (MH log risk ratio -0.519 [95% CI -0.949 - -0.089]; Z= -2.367; P=0.017).

Conclusion

POCD is a common event among CABG patients. The neuroprotective effect of low MAP on POCD was attenuated by the prolonged CPB time.

Lidocaine dose-response effect on postoperative cognitive deficit: meta-analysis and meta-regression

INTRODUCTION

The true influence of the perioperative intravenous lidocaine on the development of postoperative cognitive deficit (POCD) in coronary artery bypass grafting (CABG) remains controversial. The principal aim is to undertake a meta-regression to determine whether moderator variables mediate the relationship between lidocaine and POCD. Areas covered: We searched the Web of Science, PubMed database, Scopus and the Cochrane Library database (up to June 2017) and systematically reviewed a list of retrieved articles. Our final review includes only randomized controlled trials (RCTs) that compared infusion of lidocaine and placebo during cardiopulmonary bypass (CPB). Mantel-Haenszel risk ratio (MH RR) and corresponding 95% confidence interval (CI) was used to report the overall effect and meta-regression analysis. A total of 688 patients in five RCTs were included. POCD occurred in 34% of all cases. Perioperative lidocaine reduces POCD (MH RR 0.702 (95% CI: 0.541-0.909). Younger age, male gender, longer CPB and higher concentration of lidocaine significantly mediate the relationship between lidocaine and POCD in favour of the neuroprotective effect of lidocaine. Expert commentary: The neuroprotective effect of lidocaine on POCD is consistent in spite of longer CPB time. A higher concentration of lidocaine strengthened the neuroprotective effect of lidocaine.

Cerebral dysfunction after cardiopulmonary bypass: aetiology, manifestations and interventions

Central nervous system dysfunction following cardiac surgery remains a significant cause of morbidity and mortality, with the reported incidence of dysfunction varying widely between studies. Microemboli and global cerebral hypoperfusion are implicated as the major aetiologies of CNS impairment. Preoperative and intraoperative variables influencing the patient's risk of complications remain controversial. Based on a review of previous studies, this paper outlines the major causes and manifestations of CNS impairment as well as the intraoperative interventions currently advocated to improve the cerebral outcome of cardiac patients.

Perspective on Cerebral Microemboli in Cardiac Surgery: Significant Problem or Much Ado About Nothing?

From the time an association was perceived between cardiac surgery and post-operative cognitive dysfunction (POCD), there has been interest in arterial microemboli as one explanation. A succession of studies in the mid-1990s reported a correlation between microemboli exposure and POCD and there followed a focus on microemboli reduction (along with other strategies) in pursuit of peri-operative neuroprotection. There is some evidence that the initiatives developed during this period were successful in reducing neurologic morbidity in cardiac surgery. More recently, however, there is increasing awareness of similar rates of POCD following on and off pump cardiac operations, and following many other types of surgery in elderly patients. This has led some to suggest that cardiopulmonary bypass (CPB) and microemboli exposure by implication are non-contributory. Although the risk factors for POCD may be more patient-centered and multifactorial than previously appreciated, it would be unwise to assume that CPB and exposure to microemboli are unimportant. Improvements in CPB safety (including emboli reduction) achieved over the last 20 years may be partly responsible for difficulty demonstrating higher rates of POCD after cardiac surgery involving CPB in contemporary comparisons with other operations. Moreover, microemboli (including bubbles) have been proven harmful in experimental and clinical situations uncontaminated by other confounding factors. It remains important to continue to minimize patient exposure to microemboli as far as is practicable.

Generation, detection and prevention of gaseous microemboli during cardiopulmonary bypass procedure

Neuropsychological injury after cardiopulmonary bypass (CPB) is one of the most serious and costly complications arising from the procedure. Gaseous microemboli (GME) have long been implicated as one of the principal causes. There are two major sources of GME: surgical and manual manipulation of the heart and arteries; and the components of the extracorporeal circuit, including the type of pump, different perfusion modes, the design of the oxygenator and reservoir, and the use of vacuum assisted venous drainage (VAVD), all of which have a great impact on the delivery of existing GME to the patients. Transcranial cranial Doppler (TCD) has been used for more than two decades to assess and monitor the quality of extracorporeal perfusion with regard to the blood flow velocity of the middle cerebral arteries (MCA) and emboli detection, contributing to the achievement of better perfusion results. The Emboli Detection and Classification (EDAC) Quantifier has been able to detect and track microemboli in CPB circuits up to 1,000 microemboli per second at flow rates ranging from 0.2 L/min to 6.0 L/min. The deleterious effects of GME are multiple, including damage to the cerebral vascular endothelium, disruption of the blood-brain barrier, complement activation, leukocyte aggregation, increased platelet adherence, and fibrin deposition in the micro-vasculature. Improvements in perfusion equipment and in perfusion and surgical techniques have led to a dramatic reduction in the occurrence of GME during cardiac surgery. Although the clinical relevance of cerebral air embolization in causing neurological damage is unclear, every single person involved in perfusion and surgical technology should be aware of the risk of embolization and strictly regulate clinical behavior. Related research should also be done to improve the design of circuit components and clinical practice with a view to eliminating air bubbles during CPB procedure.

Comparison of intravenous terbutaline versus normal saline in pediatric patients on continuous high-dose nebulized albuterol for status asthmaticus

OBJECTIVE

To determine if the addition of intravenous terbutaline provides any clinical benefit to children with acute severe asthma already on continuous high-dose nebulized albuterol.

METHODS

We conducted a prospective, randomized, double blind, placebo-controlled trial on pediatric patients with acute severe asthma presenting to a large inner city tertiary children's emergency department. Consecutive patients between 2 and 17 years of age who failed acute asthma management and needed intensive care unit admission underwent informed consent and were enrolled into the study. Patients not requiring intubation were randomized to receive either intravenous terbutaline or intravenous normal saline while on continuous high-dose nebulized albuterol, ipratropium bromide, and systemic corticosteroids. Outcome measures included a clinical asthma severity score, hours on continuous nebulized albuterol, and duration of stay in the pediatric intensive care unit. In addition, electrocardiograms, electrolytes, lactic acid, and troponin I levels were obtained at routine intervals during the first 24 hours after admission. Patients who significantly worsened while enrolled in the study received intravenous aminophylline according to protocol.

RESULTS

Forty-nine patients were enrolled in the study. Patients on terbutaline had a mean improvement in the clinical asthma severity score over the first 24 hours of 6.5 points compared with 4.8 points in the placebo group (P = 0.073). Patients on terbutaline spent 38.19 hours on continuous nebulized albuterol compared with their placebo counterparts who spent 51.93 hours (P = 0.25). The length of stay in the PICU was on average 12.95 hours longer for those patients in the placebo group as compared with the terbutaline group (P = 0.345). One patient was removed from the study for a significant cardiac dysrhythmia. This patient was in the terbutaline group and recovered without complications. Troponin I values at 12 hours and 24 hours were elevated in 3 patients each, all within the terbutaline group.

CONCLUSIONS

No outcome measures demonstrated statistical significance. Outcome measures revealed a trend toward improvement in the terbutaline group. Before recommending routine use of intravenous terbutaline for acute severe asthma, further study to determine safety and efficacy is necessary.

Correlates of Neurocognitive Function of Patients After Off-Pump Coronary Artery Bypass Surgery

• Background Decreases in neurocognitive function have been reported in patients who have undergone off-pump coronary artery bypass surgery; however, few investigators have examined the correlates of the decreases.

• Objectives To explore and determine the correlates of neurocognitive function at the time of discharge from the hospital in patients undergoing off-pump coronary artery bypass surgery.

• Methods Patients undergoing off-pump coronary artery bypass surgery at Abbott Northwestern Hospital, Minneapolis, Minn, were administered tests of neurocognition (cognition and motor function), anxiety, depression, and quality of life preoperatively (within 72 hours of surgery) and postoperatively (at least 72 hours after surgery but before discharge from the hospital).

• ResultsA total of 54 patients (79.6% men), mean age 64.5 years, completed tests both preoperatively and postoperatively. When baseline function was controlled for, increased age and new-onset atrial fibrillation (F3,40= 42.97; P &lt; .001) were associated with decreases in postoperative cognitive function; increased age and anxiety (F3,35= 15.83; P &lt; .001) were associated with decreases in postoperative motor function.

• Conclusion Older patients, anxious patients, and patients with new-onset atrial fibrillation are at risk for neurocognitive changes after off-pump coronary artery bypass surgery. Further studies with larger sample sizes should be done to examine interventions to reduce preoperative anxiety in these patients. Interventions to prevent postoperative atrial fibrillation should be explored to determine whether the interventions prevent a decline in neurocognitive function.

Stroke after cardiac surgery: a risk factor analysis of 16,184 consecutive adult patients

BACKGROUND

Stroke remains a devastating complication after cardiac surgical procedures despite advances in perioperative monitoring and management. The purpose of this study was to determine the predictors of stroke in a large, contemporary cardiac surgery population.

METHODS

Prospective data on 16,184 consecutive patients undergoing cardiac surgery (coronary artery bypass grafting [CABG], n = 8,917; beating heart CABG, n = 1,842; aortic valve surgery, n = 1,830; mitral valve surgery, n = 708; double or triple valve surgery, n = 381; CABG and valve surgery, n = 2,506) between April 1996 and August 2001 were subjected to univariate and multivariate analysis. Stroke was defined as any new permanent (manifest stroke) or temporary neurologic deficit or deterioration (transient ischemic attack or prolonged reversible ischemic neurologic deficit) and was confirmed by computed tomography or magnetic resonance imaging whenever possible.

RESULTS

Overall incidence of stroke was 4.6% and varied between surgical procedures (CABG 3.8%; beating-heart CABG 1.9%; aortic valve surgery 4.8%; mitral valve surgery 8.8%; double or triple valve surgery 9.7%; CABG and valve surgery 7.4%). Of 63 patient-specific and treatment variables, 54 were found to have a significant univariate association with postoperative stroke. Multivariable analysis revealed 10 variables that were independent predictors of stroke: history of cerebrovascular disease, peripheral vascular disease, diabetes, hypertension, previous cardiac surgery, preoperative infection, urgent operation, CPB time more than 2 hours, need for intraoperative hemofiltration, and high transfusion requirement. Beating heart CABG was associated with a lower incidence of stroke in this multivariable analysis.

CONCLUSIONS

Identification of predictors for stroke is important for understanding the pathogenesis of this devastating complication as well as for developing preventative strategies. Although retrospective analyses can be subject to selection bias we believe beating heart CABG is associated with a lower incidence of stroke and may therefore improve patient outcomes.

Fat contamination of pericardial suction blood and its influence on in vitro capillary-pore flow properties in patients undergoing routine coronary artery bypass grafting

OBJECTIVE

Neurologic dysfunction after cardiopulmonary bypass might be due to arterial microembolization. Pericardial suction blood is a possible source of embolic material. Our aim was to determine the capillary-pore flow ability of pericardial suction blood.

METHODS

Pericardial suction blood from patients undergoing coronary bypass was collected, and pericardial suction blood and venous blood were sampled at the end of cardiopulmonary bypass and before reinfusion of pericardial suction blood. Pericardial suction blood was (n = 10) or was not (n = 10) prefiltered through a 30-microm cardiotomy screen filter before capillary in vitro analysis. Additionally, in 8 patients the plasma viscosity was measured, and in 5 of these patients, pericardial suction blood capillary deposits were evaluated by using a microscopy-imprint method and fat staining. Capillary flow was tested through 5-microm pore membranes. Tested components were plasma, plasma-eliminated whole-blood resuspension, and leukocyte/plasma-eliminated erythrocyte resuspension. Initial filtration rate and clogging slope expressed the blood-to-capillary interaction.

RESULTS

The plasma-flow profile of pericardial suction blood was highly impaired, with a 47% reduction in initial filtration rate (P <.001) and a 142% steeper clogging slope flow deceleration (P <.01). This difference was not due to a change in pericardial suction blood viscosity, such as by free hemoglobin, which corresponded to 5.7% of the erythrocytes. There were no differences in resuspended whole blood or erythrocytes. The cardiotomy filter had no effect. Microscopy suggested the presence of capillary fat deposits in pericardial suction blood that were not seen with venous plasma (P <.05). The pericardial suction blood volume was 458 +/- 42 mL and contained 95.6 +/- 9.3 g/L hemoglobin.

CONCLUSIONS

The pericardial suction blood plasma capillary flow function was highly impaired by liquid fat. Pericardial suction blood hemoglobin appears worth recovering after fat removal, despite profound hemolysis.

Delirium after coronary bypass surgery evaluated by the organic brain syndrome protocol

OBJECTIVE

The aim was to evaluate symptoms of delirium from a psychogeriatric perspective occurring postoperative to coronary bypass surgery.

DESIGN

Patients, > or = 60 years, scheduled for coronary bypass surgery (n = 52) were enrolled in a prospective descriptive study. The patients were evaluated before and several times after surgery by the Organic Brain Syndrome scale, and delirium was diagnosed according to psychiatric codes.

RESULTS

Of the 52 patients, 23% presented delirium. These patients were older than the control group, 73.5 +/- 4.2 and 69.3 +/- 5.9 years, respectively (mean +/- SD, p < 0.01), and had more frequently a history of previous stroke (p < 0.05). Emotional delirium was seen in 83%, hyperactive delirium in about 40%, and 25% were classified to have a psychotic delirium. A major finding was a 58% frequency of hallucinations and illusions among patients with delirium, and a similar rate among those without delirium.

CONCLUSION

Delirium is common after cardiac surgery in particular in older patients, but is often under-diagnosed. Hallucinations were common in both delirious and non-delirious patients.

The use of leucocyte-depleting and conventional arterial line filters in cardiac surgery: a systematic review of clinical studies

Although various forms of arterial line filter have been available for use during cardiopulmonary bypass (CPB) for 30 years, their use is not universal. The aim of this review was to seek evidence of the clinical benefit of using conventional or leucocyte-depleting arterial line filters during bypass. A literature search revealed 28 relevant clinical studies. Despite the wide variety of patient populations, types of filter and outcome measures utilized in studies, a few conclusions are possible. Whereas conventional filtration has the definite effect of reducing neuropsychological deficit post-CPB, the results of studies using the leucocyte-depleting filter are less clear cut. Leucocyte-depleting filters have potential for reducing inflammatory mediated heart and lung injury, however it is recommended that any additional benefit of leucocyte-depleting filters over conventional filters should be further tested by randomized controlled trials of sufficient size.

Efficiency of an air filter at the drainage site in a closed circuit with a centrifugal blood pump: an in vitro study

In a closed circuit with a centrifugal blood pump, one of the serious obstacles to clinical application is sucking of air bubbles into the drainage circuit. The goal of this study was to investigate the efficiency of an air filter at the drainage site. We used whole bovine blood and the experimental circuit consisted of a drainage circuit, two air filters, a centrifugal blood pump, a membrane oxygenator, a return circuit, and a reservoir. Air was injected into the drainage circuit with a roller pump, and the number and size of air bubbles were measured. The air filter at the drainage site could remove the air bubbles (>40 microm) by itself, but adding a vacuum removed more bubbles (>40 microm) than without vacuum. Our results suggest that an air filter at the drainage site could effectively remove air bubbles, and that adding the filter in a closed circuit with a centrifugal blood pump would be safer.

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.

Mental status change in older surgical patients. Cognition, depression, and other comorbidity

The authors studied patients age 60 and over to assess the effect of elective surgery as a precipitating factor for cognitive decline over the postoperative year. They found an association between change in test performance and age, physical disability, and number of depressive symptoms. However, persistent decline in Mini-Mental State Exam scores was associated with identifiable factors related to the initial surgery in only 3/ 251 (1 percent of cases). Depression and new onset of acute illness were confounding factors in the assessment of cognitive decline.

Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli

BACKGROUND AND PURPOSE

Many patients who undergo cardiac surgery assisted with cardiopulmonary bypass (CPB) experience cerebral injury, and microemboli are thought to play a role. Because an increased duration of CPB is associated with an increased risk of subsequent cerebral dysfunction, we investigated whether cerebral microemboli were also more numerous with a longer duration of CPB.

METHODS

Brain specimens were obtained from 36 patients who died within 3 weeks after CPB. Specimens were embedded in celloidin, sectioned 100 microm thick, and stained for endogenous alkaline phosphatase, which outlines arterioles and capillaries. In such preparations, emboli can be seen as swellings in the vessels. Cerebral microemboli were counted in equal areas and scored as small, medium, or large to estimate the embolic load (volume of emboli).

RESULTS

With increasing survival time after CPB, the embolic load declined (P<0.0001). (Lipid emboli are known to pump slowly through the brain.) Also with increasing time after CPB, the percentage of large and medium emboli became lower (P=0.0034). This decline is consistent with the concept that the emboli break into smaller globules as they pass through the capillary network. A longer duration of CPB was associated with increased embolic load (P=0. 0026). For each 1-hour increase in the duration of CPB, the embolic load increased by 90.5%.

CONCLUSIONS

Thousands of microemboli were found in the brains of patients soon after CPB, and an increasing duration of CPB was associated with an increasing embolic load.

Cerebral protection by lidocaine during cardiac operations

BACKGROUND

Lidocaine improves outcome in animal brain injury models. Cardiac operations often cause postoperative neuropsychological (NP) impairment. We investigated cerebral protection by lidocaine in cardiac surgical patients.

METHODS

Sixty-five patients undergoing left heart valve procedures completed 11 preoperative NP tests, a self-rating inventory for memory, and inventories measuring depression and anxiety. These were repeated 10 days, 10 weeks, and 6 months postoperatively. Patients received a 48-hour double-blinded infusion of either lidocaine in a standard antiarrhythmic dose or placebo, beginning at induction of anesthesia. A postoperative deficit in any test was defined as decline by more than or equal to the group preoperative standard deviation. In addition, sequential postoperative percentage change scores were calculated for each patient in all NP tests and the inventories for memory, depression and anxiety.

RESULTS

Forty-two patients completed all three reviews, 8 completed two reviews, and 5 patients were reviewed once. Significantly more placebo patients had a deficit in at least one NP test at 10 days (p<0.025) and 10 weeks (p<0.05). The lidocaine group achieved superior sequential percentage change scores in 6 of the 11 NP tests (p<0.05) and in the memory inventory (p<0.025). There were no group differences in the remaining NP tests or the depression and anxiety inventories.

CONCLUSIONS

These data show that cerebral protection by lidocaine, which is unrelated to any effect on depression or anxiety, and is at a level that is noticed by the patients.

Cerebral injury after cardiac surgery: identification of a group at extraordinary risk. Multicenter Study of Perioperative Ischemia Research Group (McSPI) and the Ischemia Research Education Foundation (IREF) Investigators

BACKGROUND AND PURPOSE

Cerebral injury after cardiac surgery is now recognized as a serious and costly healthcare problem mandating immediate attention. To effect solution, those subgroups of patients at greatest risk must be identified, thereby allowing efficient implementation of new clinical strategies. No such subgroup has been identified; however, patients undergoing intracardiac surgery are thought to be at high risk, but comprehensive data regarding specific risk, impact on cost, and discharge disposition are not available.

METHODS

We prospectively studied 273 patients enrolled from 24 diverse US medical centers, who were undergoing intracardiac and coronary artery surgery. Patient data were collected using standardized methods and included clinical, historical, specialized testing, neurological outcome and autopsy data, and measures of resource utilization. Adverse outcomes were defined a priori and determined after database closure by a blinded independent panel. Stepwise logistic regression models were developed to estimate the relative risks associated with clinical history and intraoperative and postoperative events.

RESULTS

Adverse cerebral outcomes occurred in 16% of patients (43/273), being nearly equally divided between type I outcomes (8.4%; 5 cerebral deaths, 16 nonfatal strokes, and 2 new TIAs) and type II outcomes (7.3%; 17 new intellectual deterioration persisting at hospital discharge and 3 newly diagnosed seizures). Associated resource utilization was significantly increased--prolonging median intensive care unit stay from 3 days (no adverse cerebral outcome) to 8 days (type I; P<0.001) and from 3 to 6 days (type II; P<0.001), and increasing hospitalization by 50% (type II, P=0.04) to 100% (type I, P<0.001). Furthermore, specialized care after hospital discharge was frequently necessary in those with type I outcomes, in that only 31% returned home compared with 85% of patients without cerebral complications (P<0.001). Significant risk factors for type I outcomes related primarily to embolic phenomena, including proximal aortic atherosclerosis, intracardiac thrombus, and intermittent clamping of the aorta during surgery. For type II outcomes, risk factors again included proximal aortic atherosclerosis, as well as a preoperative history of endocarditis, alcohol abuse, perioperative dysrhythmia or poorly controlled hypertension, and the development of a low-output state after cardiopulmonary bypass.

CONCLUSIONS

These prospective multicenter findings demonstrate that patients undergoing intracardiac surgery combined with coronary revascularization are at formidable risk, in that 1 in 6 will develop cerebral complications that are frequently costly and devastating. Thus, new strategies for perioperative management--including technical and pharmacological interventions--are now mandated for this subgroup of cardiac surgery patients.

Head and Heart: Neuropsychological Reaction and Arterial Line Filtration during Cardiopulmonary Bypass

As part of a prospective study of neuropsychologic reactions after cardiopulmonary bypass and their relation to arterial line filters, 44 patients who underwent elective cardiac operations were randomized into two groups. Group A had a 40-micron nylon screen filter in the arterial line. No arterial filter was used in group B. Neuropsychological examinations of all patients were conducted before and at a mean of 8 days after the operation on a double blind basis by a single trained psychologist. The tests included the Wechsler Memory Scale, the trail-making test, the Hamilton Anxiety Rating Scale, and the Hamilton Rating Scale for Depression. The 2 groups were otherwise similar with respect to preoperative neurologic and intellectual status, anesthetic methods, duration of operation, operative procedures performed, and the time spent in the intensive care unit. Surprisingly, there was a highly significant improvement in all four test scores after surgery. There were no statistically significant differences in the test scores between the two groups but considerable inter-patient performance variability was noted. The arterial line filter did not appear to have an effect on test scores. Routine use of an arterial filter remains questionable.

Normothermic Cardiopulmonary Bypass

Normothermic cardiopuhnonary bypass avoids the detrimental systemic effects of hypothermia. It is a safe and effective technique of systemic perfusion during cardiopulmonaiy bypass. Myocardial preservation is not compromised when electromechanical quiescence is maintained. Cerebral protection is comparable to that of systemic hypothermia. Low vascular resistance is common and easily treated with higher perfusion flows or vasopressors during bypass and facilitates weaning from bypass. Duration of cardiopulmonary bypass is significantly shortened by the absence of systemic cooling and rewarming phases. Clinical outcomes of patients undergoing cardiac, surgery with normothermic bypass compare favorably with those receiving moderate hypothermia.

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.

Signs of brain cell injury during open heart operations: past and present

Signs of brain cell injury have been studied during the evolution of open heart surgery in the last quarter century. At the beginning of the period, it was possible to elucidate signs of brain injury with rather crude psychometric tests and clinical observations in seemingly normal patients having routine operations. Over the next 5 years, a marked improvement in psychometric scores was observed. However, a biochemical cerebral cell injury marker (adenylate kinase) showed increased levels in the cerebrospinal fluid, a finding indicative of brain cell injury. There was a correlation between cerebrospinal fluid levels of adenylate kinase and psychometric test results as well as between the marker levels and clinical signs. Because of the relative insensitivity of the psychometric tests used and the increasing difficulty in receiving permission for spinal fluid taps, other methods were sought. Refined psychometric memory tests were used and showed that even in the 1990s, there are subtle signs of brain cell injury during open heart operations. This finding was corroborated by using a highly brain-specific and brain-sensitive biochemical cell injury marker (S-100 beta) that increased during extracorporeal circulation and showed a correlation with clinical cerebral complications.

Cerebral emboli detected during bypass surgery are associated with clamp removal

BACKGROUND AND PURPOSE

Transcranial Doppler ultrasonography detects embolic signals during coronary artery bypass surgery. The relationship between embolization and specific events of bypass surgery is unclear.

METHODS

With this technique, 20 patients undergoing bypass surgery were continuously monitored from inception to discontinuation of bypass.

RESULTS

Embolic signals were detected in all patients. Of all embolic signals, 34% were detected as aortic cross-clamps were removed, and another 24% as aortic partial occlusion clamps were removed. Only 5% were detected at inception of bypass. Rates for embolization were 15.15 embolic signals per minute at cross-clamp removal, 10.9 embolic signals per minute at partial occlusion clamp removal, and fewer than 3 embolic signals per minute at other times. Correlation was found between the number of emboli, severity of aortic atheromatosis, and neurocognitive deterioration.

CONCLUSIONS

The majority of emboli detected during coronary artery bypass grafting are associated with the release of clamps. Clamp manipulation may lead to release of aortic atheromatous debris. These emboli may be relevant to neurocognitive outcome.

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.

Cerebral injury and cardiac operations

Cerebral complications constitute the leading source of morbidity and disability after cardiac operations. The incidence of stroke after coronary artery bypass grafting has increased in tandem with the mean age of the patient population. Although many cerebral deficits resolve with time, others remain sources of disability for otherwise functional patients and detract from an otherwise successful procedure. The clinical spectrum of cerebral complications includes both neurologic and neuropsychologic deficits. Neurologic deficits include fatal cerebral injury, stroke, impaired level of consciousness, and seizures. The incidence of these deficits is 1% to 6%. Neuropsychologic deficits refer to cognitive changes, and are quantitated with tests of memory and learning and speed of visual-motor response. The incidence of these deficits is 60% to 80% at 1 week after operation and 20% to 40% at 8 weeks after operation. Central nervous system complications after cardiac operations have been attributed in large part to the effects of cardiopulmonary bypass on the brain. Potential mechanisms include macroembolization of air or particulate matter; microembolization of gas, fat, aggregates of blood cells, platelets or fibrin, and particles of silicone or polyvinylchloride tubing; and inadequate cerebral perfusion pressure. Methods of assessment include those applied during the procedure (clinical observation, assessment of cerebral blood flow and metabolism, intraoperative electroencephalography, transcranial and carotid Doppler echography, quantitative embolic measurement, and fluorescein angiography) and those performed to measure outcome (neurologic and neuropsychologic testing, computed tomographic scans, magnetic resonance imaging, and cerebrospinal fluid studies). Much of the literature regarding cerebral injury and cardiopulmonary bypass is descriptive, relating patient risk factors to the incidence of postoperative stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropsychological dysfunction after cardiopulmonary bypass: a comparison of two institutions

The authors compared perioperative neuropsychologic dysfunction in patients participating in two studies conducted in institutions using different strategies to manage cardiopulmonary bypass. These differences included hypothermia versus normothermia, presence versus absence of arterial microfilters, and the presence versus absence of glucose-containing solution in the pump prime. Other differences between the two institutions included the type of surgery (intracardiac v extracardiac), the mean duration of cardiopulmonary bypass, and degree of low perfusion pressure during bypass. Despite these major differences, perioperative neuropsychologic dysfunction measured by the two-part Trail-Making psychometric test was similar in the two institutions. Several factors were analyzed for their possible contribution to development of dysfunction, including institution, anesthetic management, age, sex, degree of low perfusion pressure during bypass, and duration of bypass; only age was significant. These results suggest that differences in surgical procedure and management of cardiopulmonary bypass previously thought to contribute to the development of subtle cognitive deficits after cardiac surgery may have been overemphasized.

Perioperative stroke. Part II: Cardiac surgery and cardiogenic embolic stroke

The major mechanism of stroke in cardiac surgery is embolization. The risk is higher in intracardiac than in extracardiac surgery. The incidence of stoke associated with CABG is about 5%. The cerebral protective properties of isoflurane and thiopentone, acid-base management, and monitoring of cerebral perfusion during cardiopulmonary bypass are discussed. Prophylactic carotid endarterectomy for patients with asymptomatic carotid disease before cardiac surgery is not necessary. Symptomatic carotid disease increases the risk of stroke, and the management of patients who have both symptomatic coronary and carotid artery diseases is discussed. Cardiogenic embolism is probably responsible for many perioperative strokes. Patients with atrial fibrillation, valvular disease, and prosthetic heart valves are at high risk of cardiogenic embolism. Strokes associated with cardioversion, pacemaker insertion, coronary arteriography and angioplasty are explored.

Gastrointestinal complications in 4473 patients who underwent cardiopulmonary bypass surgery

Thirty-nine gastrointestinal complications occurred in 35 of 4473 patients (0.78 per cent) who underwent surgery involving cardiopulmonary bypass during an 8-year period. The mortality rate when one of these complications occurred was 22 (63 per cent) representing 11.5 per cent of the 191 deaths from all causes in the series. The relative risk of developing a gastrointestinal complication was 1:249 when the heart was not opened, 1:66 when it was and 1:5 after cardiac transplantation. Gastrointestinal bleeding (n = 20) was the most common complication of whom nine (45 per cent) died, followed by intestinal infarction (n = 12) with eight (67 per cent) deaths and acute pancreatitis (n = 6) all of whom died. There was one death after surgery for gastrointestinal bleeding (n = 7). No patient survived bowel infarction without operation but resection was possible in five of the eight who underwent surgery, four of whom survived. The results demonstrate that surgical intervention is not associated with undue mortality but inappropriate conservative therapy is poorly tolerated in this high-risk group.

Hypercarbia depresses cerebral oxygen consumption during cardiopulmonary bypass

No human studies have systematically examined the relations among PaCO2, cerebral blood flow, and the cerebral metabolic rate for oxygen during hypothermic cardiopulmonary bypass. We varied PaCO2 during hypothermic (26-28 degrees C) cardiopulmonary bypass and estimated the cerebral metabolic rate for oxygen by multiplying cerebral blood flow (measured using xenon-133 clearance) by the cerebral arteriovenous difference in oxygen contents. Patients were randomly assigned to either of two methods of managing PaCO2 (uncorrected for body temperature). In group 1 (PACO2 32-48 mm Hg, n = 13) the mean +/- SD cerebral metabolic rate for oxygen was 0.40 +/- 0.11 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 36 +/- 2.0 mm Hg and 0.40 +/- 0.14 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 45 +/- 2 mm Hg. and 49-72 mm Hg, n = 12) the mean +/- SD cerebral metabolic rate for oxygen was 0.31 +/- 0.09 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 55 +/- 3 mm Hg and 0.21 +/- 0.07 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 68 +/- 2 mm Hg. Group 2 values differed significantly from those in Group 1 (p less than 0.05). In both groups, cerebral blood flow increased as PaCO2 increased. During cardiopulmonary bypass, increasing PaCO2 increases cerebral blood flow and decreases the cerebral metabolic rate for oxygen.

Thiopental sodium by single bolus dose compared to infusion for cerebral protection during cardiopulmonary bypass

The authors previously demonstrated that thiopental sodium infused throughout cardiopulmonary bypass (CPB) considerably reduced persistent but not transient neuropsychiatric complications after open-chamber cardiac operations. Based on the probability that emboli released at the time of aortic declamping cause most postoperative central nervous system (CNS) dysfunction, this study was designed to test whether administration of a single bolus dose of thiopental before aortic declamping provided cerebral protection equal to that of infusion throughout bypass as well as a decrease in unwanted side effects. One hundred adult patients undergoing open-chamber cardiac operations with CPB received either thiopental sodium by infusion throughout CPB (n = 52) or thiopental sodium 15 mg/kg by bolus before aortic declamping (n = 48). In 90% of the patients, thiopental sodium 15 mg/kg produced electroencephalographic (EEG) burst suppression, with more than 60 seconds between bursts. Postoperative CNS dysfunction occurred in 3 (6%) of the infusion group patients (thiopental sodium 36 +/- 10 mg/kg) and 2 (4%) of the bolus group patients (thiopental sodium 16 +/- 2 mg/kg). CNS dysfunction persisting to the tenth postoperative day occurred in only one patient, who was in the infusion group. Requirements for inotropic support on separation from CPB did not differ between groups, but average time to extubation was 2.7 hours shorter in the bolus group. The authors conclude that thiopental sodium 15 mg/kg given as a single bolus immediately before aortic declamping without the need for EEG monitoring provided the same brain protection as larger doses given by infusion titrated to burst suppression, but it did not reduce the need for inotropic support during separation from CPB.

Reversed intracranial blood flow in patients with an intra-aortic balloon pump

As a preliminary investigation into the cerebral effects of mechanical cardiac assist devices, using transcranial Doppler ultrasonography I examined the basal cerebral arteries in three patients placed on an intra-aortic balloon pump. Unassisted systoles had normal blood velocities and waveforms. When the pump was in use, diastolic blood velocity during balloon inflation increased. As the balloon was deflated and intra-aortic pressure was dramatically lowered, diastolic blood velocity within the intracranial vessels decreased sharply. In two patients there was a reversal of blood flow in the middle cerebral, anterior cerebral, basilar, and vertebral arteries during late diastole. Although the clinical effects of cessation and reversal of blood flow in the cerebral circulation while on an intra-aortic balloon pump remain to be determined, transcranial Doppler ultrasonography appears to be a useful tool for measuring these hemodynamic effects. It may also be helpful in quantifying the effects of such pumps on cerebral blood flow and devising inflation/deflation timing sequences that maximize forward blood flow.

Cognitive function in patients with symptomatic dilated cardiomyopathy before and after cardiac transplantation

Pre- and postoperative cognitive performance of candidates for heart transplantation was examined by means of an extensive battery of neuropsychological measures. A total of 54 patients completed the preoperative cognitive protocol, 20 of whom also completed postoperative testing. Age (less than 50 or greater than or equal to 50 years of age) and the primary cause of cardiac deterioration (idiopathic, ischemic disease or rheumatic/congenital defects) were the major classification variables. The main findings of this study were: 1) Preoperative neuropsychological measures revealed a high frequency of impaired performance, particularly in measures of memory, higher level processing of information and motor speed. A pattern consistent with diffuse rather than focal or lateralized cerebral deficits was observed. Significant differences were not found on the basis of the cause of cardiac disease, but some were observed for age (the older group was more impaired). 2) A comparison of pre- and postoperative cognitive scores failed to show significant cognitive improvement despite greatly improved physical health. The cause of cardiac deterioration was not differentially associated with postoperative cognitive performance, and there was equivocal evidence for age effects. These findings may have implications for the selection of transplant recipients and the timing of transplantation surgery.

Effect of intraoperative intervention on neurological outcome based on electroencephalographic monitoring during cardiopulmonary bypass

Neurological complications of cardiopulmonary bypass procedures are well documented. The present two-part study was undertaken to (1) determine if on-line computerized electroencephalographic changes correlated with neurological outcome and (2) compare neurological outcome with that of a second group of patients who received intraoperative interventions based on electroencephalographic data. Part 1 consisted of monitoring 50 patients. A power drop index was developed that correlated with new global neurological deficits. New global deficits occurred in 44% of the patients. In part 2, this information was used to design intervention criteria. Treatment protocols used previously accepted methods of increasing cerebral blood flow, ie, increasing pump flow, raising mean arterial pressure, and increasing CO2 content in the ventilator blend. Global neurological deficits were reduced to 5% in a group of 41 clinically similar patients (p less than 0.001). Cerebral perfusion pressures were similar in both groups. The single correlating factor was the power drop index as identified by computerized EEG. Our conclusion is that simple intervention guided by computerized EEG can reduce global neurological deficits in patients having cardiopulmonary bypass procedures.

The effect of arterial filtration on reduction of gaseous microemboli in the middle cerebral artery during cardiopulmonary bypass

Noninvasive in vivo detection of gaseous microemboli in the middle cerebral artery, by transcranial Doppler ultrasound, was used to determine the effect of filtration in the arterial catheter using 25- and 40-microns filters and bubble oxygenators in patients undergoing cardiopulmonary bypass surgery. Eighteen patients undergoing coronary artery bypass surgery were studied using a closed cardiac (unvented heart) model. Group 1 patients (no filters) had the highest incidence of gaseous microemboli, as indicated by the ultrasound microemboli index, at both high and low oxygen flow rates. Group 2 patients (40-microns filters) had a significantly lower microemboli index, particularly at low oxygen flow rates (t = 4.9, p less than 0.001). The 25-microns group patients had the lowest values of all. No microemboli were detected at low oxygen flow rates, and microemboli were detected in only 0.1% of the samples at high oxygen flow rates. Additionally, observations on vented hearts in 3 patients undergoing cardiac valve surgery indicate that the origin of gaseous microemboli may be air trapped inside the heart.

The detection of microemboli in the middle cerebral artery during cardiopulmonary bypass: a transcranial Doppler ultrasound investigation using membrane and bubble oxygenators

Twenty-seven patients were examined who were undergoing cardiopulmonary bypass (CPB) surgery with either a bubble oxygenator or a capillary membrane oxygenator. The latter incorporated an arterial filter and bubble trap. A noninvasive Doppler ultrasound technique is described for monitoring irregularities in the Doppler flow signals attributable to gaseous microemboli detected in the middle cerebral artery during CPB. The ultrasound index for detecting gaseous microemboli (MEI) indicated the presence of such microemboli in 22 of the 27 patients during insertion of the aortic cannula. Measurements during CPB showed the MEI ranged from 4 to 39 in the 17 patients with a bubble oxygenator. However, all 10 patients with a membrane oxygenator had an MEI of 0. Varying the gas flow rates in 3 patients with bubble oxygenators showed a change in MEI from 4 +/- 4 (SD) at a flow rate of 2 L/min to 17 +/- 9 at a flow rate of 5 L/min. This observation supports the assumption that the MEI is providing quantitative information regarding the presence of gaseous emboli in the middle cerebral artery.