Arterial line filtration protects brain microcirculation during cardiopulmonary bypass in the pig

Increased Transcription Factor Expression and Permeability of the Blood Brain Barrier Associated With Cardiopulmonary Bypass in Lambs

BACKGROUND

The pathophysiology of neurocognitive dysfunction and developmental delay after cardiopulmonary bypass (CPB) in infants is not known. It is known that head trauma, stroke, and seizures cause dysfunction of the blood brain barrier (BBB) that is associated with increased inducible transcription factor gene expression in the cells of the barrier. The purpose of this study was to determine the effects of CPB and hypothermic circulatory arrest on expression of the transcription factor FOS and the function of the BBB in an infant animal model.

METHODS

Infant lambs (n = 36; 10-12 days) were exposed to 0, 15, 30, 60, or 120 minutes of normothermic (38 degrees C) CPB or 2 hours of hypothermic circulatory arrest at 16 degrees C. After terminating bypass 15 animals had their brains perfusion-fixed and removed for immunohistochemical analysis of expression of the transcription factor FOS. The other animals were perfused with fluorescent albumin to visualize the brain microvasculature. Brain sections were analyzed with a laser scanning confocal microscope.

RESULTS

Control animals (n = 6, sham operated and cannulated) exhibited normal vasculature with negligible leakage and no FOS protein expression in neurons or endothelial cells anywhere in the brain. Significant FOS expression in barrier-associated structures including the blood vessels, choroid plexus, and ependyma but not neurons occurred at all times on bypass. CPB caused leakage of fluorescent albumin from blood vessels in all animals. Two hours of normothermic CPB (n = 4) caused significant (p < 0.01) leakage in the cerebellum, cortex, hippocampus, and corpus callosum. Animals exposed to circulatory arrest experienced severe leakage throughout the brain (p < 0.001) and FOS expression in all cells.

CONCLUSIONS

These experiments indicate that the BBB is dysfunctional after all time points on normothermic CPB, BBB dysfunction is worsened by hypothermic circulatory arrest, and BBB dysfunction is associated with intense molecular activity within the barrier-forming cells. Dysfunction of the BBB may contribute to neurologic complications after heart surgery.

The dynamic air bubble trap reduces cerebral microembolism during cardiopulmonary bypass

OBJECTIVE

Neuropsychologic disorders are common after coronary artery bypass operations. Air microbubbles are identified as a contributing factor. A dynamic bubble trap might reduce the number of gaseous microemboli.

METHODS

A total of 50 patients undergoing coronary artery bypass operation were recruited for this study. In 26 patients a dynamic bubble trap was placed between the arterial filter and the aortic cannula (group 1), and in 24 patients a placebo dynamic bubble trap was used (group 2). The number of high-intensity transient signals within the proximal middle cerebral artery was continuously measured on both sides during bypass, which was separated into 4 periods: phase 1, start of bypass until aortic clamping; phase 2, aortic clamping until rewarming; phase 3, rewarming until clamp removal; and phase 4, clamp removal until end of bypass. S100 beta values were measured before, immediately after, and 6 and 48 hours after the operation and before hospital discharge.

RESULTS

The bubble elimination rate during bypass was 77% in group 1 and 28% in group 2 (P <.0001). The number of high-intensity signals was lower in group 1 during phase 1 (5.8 +/- 7.3 vs 16 +/- 15.4, P <.05 vs group 2) and phase 2 (6.9 +/- 7.3 vs 24.2 +/- 27.3, P <.05 vs group 2) but not during phases 3 and 4. Serum S100 beta values were equally increased in both groups immediately after the operation. Group 2 patients had higher S100 beta values 6 hours after the operation and significantly higher S100 beta values 48 hours after the operation (0.06 +/- 0.14 vs 0.18 +/- 0.24, P =.0133 vs group 2). Age and S100 beta values were correlated in group 2 but not in group 1.

CONCLUSION

Gaseous microemboli can be removed with a dynamic bubble trap. Subclinical cerebral injury detectable by increases of S100 beta disappears earlier after surgical intervention.

Changes in jugular bulb oxygenation in patients undergoing warm coronary artery bypass surgery (34-37 degrees C)

BACKGROUND AND OBJECTIVE

Imbalance between cerebral oxygen supply and demand is thought to play an important role in the development of cerebral injury during cardiac surgery with cardiopulmonary bypass.

METHODS

We studied jugular bulb oxygen saturation, jugular bulb oxygen tension, arterial-jugular bulb oxygen content difference and oxygen extraction ratio in 20 patients undergoing warm coronary artery bypass surgery (34-37 degrees C) with pH-stat blood gas management.

RESULTS

Only two patients showed desaturation (jugular bulb oxygen saturation < 50%) at 5 min on bypass, and none from 20 min onwards. Multiple regression models were performed after using bypass temperature, mean arterial pressure, cerebral perfusion pressure, haemoglobin concentration and arterial carbon dioxide tension as independent variables, and arterial-jugular bulb oxygen content difference, jugular bulb oxygen saturation, oxygen extraction ratio and jugular bulb oxygen tension as individual dependent variables.

CONCLUSIONS

We found that jugular bulb oxygen saturation, jugular bulb oxygen tension and oxygen extraction ratio are mainly dependent on arterial carbon dioxide tension, and arterial-jugular bulb oxygen content difference is dependent on arterial carbon dioxide tension and the bypass temperature. Our results suggest jugular bulb oxygenation is mainly dependent on arterial carbon dioxide tension during warm cardiopulmonary bypass.

Central Nervous System Complications in Cardiac Surgery: Retrograde Cerebral Perfusion, Pressure, Pulsatility, Temperature, and pH Management During Cardiopulmonary Bypass

Currently, clinical management strategies during cardio pulmonary bypass (CPB) are undergoing profound changes. Renewed interest in normothermic versus hypothermic perfusion during CPB has resulted in appar ently contradictory results regarding patient outcomes. Much effort has been devoted to defining physiological responses of the brain to various alterations during CPB (eg, pH strategy, normothermia versus hypothermia, pulsatile or nonpulsatile perfusion, use of arterial line filtration, circulatory arrest, retrograde cerebral perfu sion). In addition, prospective studies are examining the impact of diverse strategies on neuropsychological and neurological outcomes after CPB, to define optimal management techniques.

Neurodevelopmental outcome and lifestyle assessment in school-aged and adolescent children with hypoplastic left heart syndrome

OBJECTIVES

The purposes of this study are to describe the quality of life and cognitive function in school-aged children who have undergone staged palliation for hypoplastic left heart syndrome (HLHS), and to identify factors that are predictive of neurodevelopmental outcome in this population.

METHODS

School-aged survivors with HLHS who had undergone palliative surgery at our institution were identified and mailed a questionnaire to assess subjectively quality of life, school performance, and incidence of medical complications. A subgroup of local patients underwent standardized testing of cognitive function and neurologic examination. These patients were compared with the larger (remote) group of questionnaire respondents to determine whether results may be generalizable to the entire HLHS population. Potential predictors of neurologic and cognitive outcome were tested for their association with test scores using multivariate regression analysis.

RESULTS

Questionnaire results were obtained from 115 of 138 eligible children (83%; mean age: 9.0 +/- 2.0 years). Standardized testing was performed in 28 of 34 (82%) eligible local patients (mean age: 8.6 +/- 2.1 years). The majority of parents or guardians described their child's health as good (34%) or excellent (45%) and their academic performance as average (42%) or above average (42%). One third of the children, however, were receiving some form of special education. Chronic medication usage was common (64%); the incidence of medical complications was comparable to that previously reported in children with Fontan physiology. Cognitive testing of the local group demonstrated a median full scale IQ of 86 (range: 50-116). Mental retardation (IQ: <70) was noted in 18% of patients. In multivariate analysis, only the occurrence of preoperative seizures predicted lower full scale IQ.

CONCLUSIONS

Although the majority of school-aged children with HLHS had IQ scores within the normal range, mean performance for this historical cohort of survivors was lower than that in the general population.

Review on the multifactorial aspects of bioincompatibility in CPB

Over the last few years, a great emphasis has been placed on the bioincompatibility of foreign, nonphysiological materials used during CPB. It is only recently that bioincompatibility has objectively been recognized to be multifactorial, with the dominant implicated sources being cardiotomy blood suction, shear stresses or flow dynamics and, to a lesser degree, the blood/artificial surface interactions, the heparin/protamine complex and the various forms of emboli or debris. In summary, in CPB, the reduction of postoperative complications, such as whole body inflammatory reactions, bleeding and organ dysfunctions, can only be impacted if the primary, dominant sources of bioincompatibility are reduced or eliminated.

Determinants of cerebral perfusion during cardiopulmonary bypass

The risk of postoperative neurologic dysfunction in patients undergoing cardiac surgery remains high despite continued improvements in myocardial protective strategies. Part of this neurologic morbidity can be attributed to patients' increased age and underlying pathology, but other factors adversely affecting cerebral blood flow and cerebral metabolism during cardiopulmonary bypass may also contribute. Particulate microembolization during cardiopulmonary bypass appears to be a major cause of postoperative neurologic dysfunction and the pH-stat method of carbon dioxide management during hypothermia may potentiate neurologic damage by allowing a greater embolic load to be delivered to the brain. Echocardiography and transcranial Doppler methods may contribute to reducing the incidence of cerebral embolization by recognizing the timing and number of microemboli. Although hypothermia confers cerebral protection, rewarming may unmask and perhaps potentiate any ischemic damage that occurred with embolization during hypothermia. Both the degree and speed of rewarming may be important factors contributing to the extent of ischemic damage and ultimately neurologic function. In addition, many other factors related to cardiopulmonary bypass can alter cerebral perfusion and metabolism, such as nonpulsatile flow, hemodilution, pressure autoregulation, anesthetic and cerebroprotective drugs, and the neuroimmune response to bypass. In this review, the major factors affecting cerebral blood flow during cardiopulmonary bypass are discussed and their relative importance evaluated with regard to postoperative neurologic function.

Cerebrovascular assessment of the high-risk patient: the role of transcranial Doppler ultrasound

With increased attention to the causes and effects of neurologic injury related to cardiopulmonary bypass anesthesia and surgery, multiple modality examination and monitoring of cerebral function and perfusion in the perioperative period may prove to be advantageous. Transcranial Doppler examination and monitoring is inexpensive, noninvasive, safe, provides unique information about the functional status of the intracranial circulation, and complements the duplex Doppler study of the extracranial carotid vessels of the neck for preoperative evaluation of the surgical patient. The transcranial Doppler examination permits quantitation of blood flow velocity of the intracranial vessels, evaluation of autoregulatory capacity and vasomotor reserve, determination of symmetry of flow velocity in the circle of Willis, assessment of collateral circulatory capacity, examination of vessels not accessible to the duplex Doppler and serves as a baseline for intraoperative monitoring and the postoperative examination. Noninvasive, unilateral or bilateral, continuous monitoring of brain blood flow velocity intraoperatively or postoperatively with trending, storage, and correlation with other physiologic variables provides evidence of cerebral perfusion, occurrence and rate of cerebral embolism, and continuous monitoring of therapeutic interventions. A review of the incidence of stroke and neuropsychologic deficit after bypass surgery is focused on parameters amenable to diagnosis using transcranial Doppler. Patient-specific risk factors for neurologic injury derived from previous studies are discussed as well as risk factors that are related to anesthetic and surgical management and equipment. A description of Doppler technology and the correlation of transcranial Doppler findings with angiography and radionucleotide scans establishes the accuracy of the Doppler examination. The preoperative examination, provocative tests of vasomotor reserve, the evaluation of cerebral collateral circulation, and examples of Doppler applications are discussed.

Cardiopulmonary bypass for adult patients: a survey of equipment and techniques

OBJECTIVES

The techniques and equipment used for cardiopulmonary bypass for adult cardiac surgery vary among institutions and may change over time. This study sought to document the changing patterns of practice.

DESIGN

Voluntary survey of meeting participants.

SETTING

13th Annual San Diego Cardiothoracic Surgery Symposium (February 1993).

PARTICIPANTS

There were 331 responses from perfusionists (79.5%), cardiac surgeons (11.2%), and anesthesiologists (6.3%). The majority of these participants were from institutions where more than 1,000 cardiac operations were performed annually.

MEASUREMENTS AND MAIN RESULTS

It was found that 91.5% of the respondents used membrane oxygenators currently, compared with 5% in 1982 (as reported in a previous survey). Over 80% of the institutions surveyed used some type of perioperative cell-salvaging technique. Arterial line filters were used by 92% of the respondents compared with 64% in 1982. Also, 80% of the respondents were aware of the availability of leukocyte-depleting filters.

CONCLUSIONS

The probable reasons for the increased utilization of membrane oxygenators and arterial line filters include less damage to the formed elements of blood, fewer gaseous microemboli, and better control of carbon dioxide elimination and oxygenation. The authors anticipate that future surveys will document increased use of leukocyte-depleting filters because of the literature implicating neutrophils as mediators of tissue destruction in various disease processes, including myocardial reperfusion injury.

The role of CPB management in neurobehavioral outcomes after cardiac surgery

Recent developments in techniques for managing cardiopulmonary bypass are outlined with a view toward interventions aimed at decreasing the incidence of perioperative central nervous system dysfunction and overt stroke. Recent reports assessing central nervous system dysfunction after hypothermic and normothermic cardiopulmonary bypass are reviewed and critiqued along with data assessing techniques for cerebral protection during hypothermic circulatory arrest. Controversy surrounding optimal pH management is explored along with a proposal that pH-stat may be most satisfactory to ensure better brain cooling where circulatory arrest is anticipated, whereas alpha-stat may avoid cerebral hyperemia and thus decrease the cerebral embolic load during moderate hypothermic cardiopulmonary bypass. Newer developments in cerebral monitoring techniques are also reviewed.