Cardiopulmonary bypass and the inflammatory response: a role for serine protease inhibitors?

Protective Effects of Acupuncture in Cardiopulmonary Bypass-Induced Lung Injury in Rats

Acute lung injury caused by cardiopulmonary bypass (CPB) increases the mortality after cardiac surgery. Our previous clinical study suggested that electroacupuncture (EAc) has a protective effect during CPB, but the mechanism was unclear. So, we design this study to investigate the effects of EAc on CPB-induced lung injury and the underlying mechanism. Male Sprague Dawley rats were randomly divided into control, CPB, and CPB + EAc groups. A lung injury model was created by CPB surgery to serve as the CPB group, and EAc (2/100 Hz) was used before CPB in the CPB + EAc group. Lung tissue was collected at 0.5, 1, and 2 h after CPB. Pulmonary malondialdehyde (MDA) concentrations as well as superoxide dismutase (SOD), myeloperoxidase (MPO), and caspase-3 activity were determined. c-Jun N-terminal kinase (JNK), ERK, p38 and cleaved caspase 3 in the lung were analyzed by western blotting. A549 cells were treated by rat serum from the CPB and CPB + EAc groups, and cleaved caspase-3 activity was detected by fluorescent immunohistochemistry. CPB significantly increased the MPO activity, MDA content, apoptosis, caspase-3 activity, and phosphorylated p38 but decreased SOD activity compared with the control group. EAc significantly increased SOD activity at 0.5 and 2 h (p < 0.01 vs CPB) and reduced CPB-induced histological changes, MPO activity at 1 and 2 h (p < 0.05 vs CPB), MDA content at 2 h (p < 0.05 vs CPB), caspase-3 activity at 1 h (p < 0.05 vs CPB), and phosphorylated p38 and JNK at 0.5 h after CPB. The serum from the CPB group increased more positive staining cells of cleaved caspase-3 than that from the CPB + EAc group. EAc reversed the CPB-induced lung inflammation, oxidative damage, and apoptosis; the mechanism may involve decreased phosphorylation of p38 along with caspase-3 activity and activation.

Leukocyte filtration and aprotinin: synergistic anti-inflammatory protection

Cardiopulmonary bypass activates an array of cellular and humoral inflammatory mechanisms that culminate in diverse or organ-specific injury. A manifestation of inflammatory injury to the heart, atrial fibrillation ranks among the most frequent and potentially life-threatening postsurgical complications. Pulmonary manifestations of the inflammatory response are also of major concern. Neutrophils activated by passage through the extracorporeal circuit inflict local injury and provoke the inflammatory cascade by producing oxyradicals and proinflammatory factors. This study tested if a combination of leukocyte depletion and aprotinin suppression of neutrophils could minimize postbypass atrial fibrillation and pulmonary dysfunction. In part one, two randomized groups of 90 patients undergoing primary coronary artery bypass grafting received full Hammersmith aprotinin alone (control group) or combined with leukofiltration (study group) and were prospectively examined. The dual treatment decreased the incidence of postoperative atrial fibrillation (7 of 90, 7.8%) by 67% versus aprotinin alone (21 of 90, 23.3%). Respiratory gas exchange in these patients was assessed from pulmonary shunt fraction. In the first two hours postbypass, pulmonary shunt fraction in the dual treatment group increased 40% less than in the group receiving aprotinin alone (p = 0.002), and subsided more quickly and completely over the next six hours. In part two, the cardiopulmonary bypass group receiving aprotinin+leukofiltration was retrospectively compared with 45 patients undergoing off-pump coronary revascularization. A strong, albeit not statistically significant trend (p= 0.08) toward a lower incidence of atrial fibrillation was found in the dual treatment group versus the off-pump group (8 of 45, 17.8%). These findings suggest that combining mechanical and pharmacologic suppression of the systemic inflammatory response could mitigate its deleterious arrhythmic and pulmonary complications.

Adverse Central Nervous System Outcomes After Cardiopulmonary Bypass: A Beneficial Effect of Aprotinin?

This review considers the evidence for potential central nervous system benefits associated with use of anti- protease therapy for patients undergoing procedures involving cardiopulmonary bypass. Unfortunately, few randomized, controlled clinical trials have assessed the lysine analogue class of antifibrinolytics (ie, ∈-amino caproic acid, tranexamic acid) compared with the num ber investigating the efficacy of the enzyme-inactivator class of antifibrinolytic typified by the nonspecific serine protease inhibitors aprotinin and nafamostat.

Topical application of aprotinin in cardiac surgery

The aim of our study was to compare a systemic and a local aprotinin application in patients during coronary artery bypass graft (CABG) surgery. The advantage of a topical aprotinin application is seen in the fact that this may not lead to systemic side effects. A prospective, randomized study comprising 97 patients was conducted. A dose of 5 106 KIU aprotinin was given systemically to 49 patients and four doses of 1.25 106 KIU aprotinin were applied topically to 48 patients by spraying the substance on the target area (A. mammaria interna region and pericardium). We determined markers for the inflammatory response, coagulation system, standard haematological markers and postoperative complications. Exclusion criteria were defined as surgical bleeding, redo operations, neurological, haematological, liver and kidney disorders. Sex, age, perfusion times, mortality, renal failure and strokes were identical in both groups. Biochemical markers and clinical outcome demonstrated no significant differences between the systemic and local applications. Interleukin 6 and elastase were tendentially higher ( p= 0.1) in the local group, but with a high standard deviation in each patient. Our results suggest that there is no difference between the perioperative application of 5 106 KIU systemically given aprotinin and 1.25 106 KIU locally applied aprotinin.

Pathophysiological Basis of CNS Injury in Cardiac Surgical Patients: Detection and Prevention

The current understanding of adverse central nervous system (CNS) events following cardiac surgery involves several identifiable, evidence-based mechanisms: athero-sclerotic emboli, microgaseous and microparticulate emboli, and hypoperfusion.1 Secondary factors, including patient co-morbidities and inherent genetic susceptibilities, as well as systemic inflammatory processes and a suboptimal metabolic milieu may interact to potentiate the extent of injury.2 In this review a number of these factors and their potential interactions will be explored with a view towards developing a comprehensive management strategy to minimize CNS injury.

Aprotinin attenuates genomic expression variability following cardiac surgery

BACKGROUND

Aprotinin was the subject of recent controversy regarding adverse clinical outcomes following cardiac surgery. We compared the role of Aprotinin and epsilon-aminocaproic acid on clinical outcomes and the attenuation of the postcardiopulmonary bypass (CPB) response at the genomic expression and cytokine (protein) level.

METHODS

Thirty-nine low-risk patients undergoing coronary revascularization (CABG) and/or valve procedures using cardiopulmonary CPB were enrolled into a prospective cohort study. Aprotinin or epsilon-aminocaproic acid was administered to patients. Gene expression was assessed from whole blood mRNA samples collected preoperatively (PRE) and 6 hours (6H) postoperatively. Validation of gene expression was performed with SYBR Green real-time polymerase chain reaction. Cytokine values were quantified from serum preoperatively and postoperatively at 6 H and 4 days and analyzed in a blinded fashion.

RESULTS

No difference was detected in baseline characteristics. Inflammatory markers measured did not reveal significant difference between patients receiving Aprotinin (APR) and those receiving epsilon-aminocaproic acid (Amicar). Intraoperative parameters and postoperative outcomes were not significantly different. Compared with PRE samples, 6H samples had 264 upregulated and 548 downregulated genes uniquely in the APR group compared to 4826 upregulated and 1114 downregulated genes uniquely in the Amicar group (p < 0.001). Compared to patients in the Amicar group, APR patients had significantly different gene expression pathways involving NF-kappabeta regulation, programmed cell death and cell-cell adhesion. None of the patients developed postoperative stroke, myocardial infarction, or systemic infections.

CONCLUSIONS

Aprotinin leads to significantly less genomic expression variability following CPB compared to Amicar and has a differential effect on specific genomic pathways.

Hippocampus bcl-2 and bax expression and neuronal apoptosis after moderate hypothermic cardiopulmonary bypass in rats

Using a rat model of moderate hypothermic (26 degrees C-28 degrees C) cardiopulmonary bypass (CPB) with hemodilution, we investigated hippocampal apoptotic gene expression and neuronal apoptosis up to 6 h after CPB. The CPB was performed on male rats (380-400 g) under general anesthesia with isoflurane and fentanyl. The right atrium and tail artery were cannulated, and a peristaltic pump and membrane oxygenator were used for CPB. Two groups were studied: Group 1 consisted of fasted rats (n = 15) subjected to 60 min of moderate hypothermic nonpulsatile CPB; Group 2 consisted of sham-operated rats (n = 15). At 1 h after CPB, in 6 rats per group, hippocampus was processed for the apoptotic gene (bcl-2 and bax) messenger RNAs detection by reverse transcriptase polymerase chain reaction, and messenger RNA expression was determined by the ratio of the polymerase chain reaction product of bcl-2 or bax to the beta-actin gene. At 6 h after CPB, in 6 rats per group, hippocampus expression of Bcl-2 and bax protein was determined by immunohistochemistry, and neuronal apoptosis was detected by TUNEL. At 6 h after CPB, in three rats per group, changes in hippocampal CA1 neuronal ultra structure were determined with electron microscopy. Group 1 had increased ratios of bcl-2/beta-actin, bax/beta-actin, and bax/bcl-2 mRNA at 1 h after CPB (bcl-2/beta-actin, 0.82 +/- 0.14 versus 0.63 +/- 0.07; P = 0.03; bax/beta-actin, 1.04 +/- 0.14 versus 0.56 +/- 0.03; P = 0.00; bax/bcl-2, 1.31 +/- 0.12 versus 0.84 +/- 0.09; P = 0.02; Group 1 versus Group 2, respectively). Group 1 had increased bcl-2 and bax protein expression in hippocampal CA1 region at 6 h after CPB (bcl-2, 0.18 +/- 0.05 versus 0.09 +/- 0.01; P = 0.02; bax, 0.20 +/- 0.06 versus 0.04 +/- 0.02; P = 0.01; Group 1 versus Group 2, respectively). Group 1 had increased TUNEL staining in hippocampus CA1 at 6 h after CPB (0.14 +/- 0.02 versus 0.03 +/- 0.01; P = 0.00; Group 1 versus Group 2, respectively). In Group 1 CA1 hippocampus neurons, ultra-structural changes consistent with apoptosis occurred. In rats, moderate hypothermic CPB with hemodilution is associated with CA1 hippocampus bax and bcl-2 gene expression and neuronal apoptosis during the early post-CPB recovery period.

Effect of aprotinin on the frequency of postoperative atrial fibrillation or flutter

PURPOSE

The relationship between adding aprotinin to standard care and the frequency of postoperative atrial fibrillation or flutter (POAF) in patients undergoing cardiothoracic surgery (CTS) with cardiopulmonary bypass (CPB) was studied.

METHODS

This was a retrospective cohort evaluation. All patients at a hospital who underwent CTS with CPB between October 1999 and October 2003 and who received aprotinin during surgery were included in the treatment group. Control patients were those who did not receive aprotinin; they were matched with treatment group patients for age, valvular surgery, history of atrial fibrillation or flutter, renal dysfunction, peripheral artery disease, smoking, angina, diabetes mellitus, congestive heart failure, previous CTS, sex, beta-blocker intolerance, and use of preoperative digoxin. The primary endpoint was POAF; secondary endpoints were perioperative transfusion use, length of stay (LOS), stroke, myocardial infarction, renal failure, graft occlusion, and death.

RESULTS

A total of 438 patients (219 per group) were evaluated. The patients' mean age was 68 years, 67% were men, and 74% had had valvular surgery. Patients who received aprotinin (mean +/- S.D. dose, 2.75 million +/- 1.24 million kallikrein-inhibiting units) did not have a significantly lower frequency of POAF than control patients (28% versus 27%, respectively [p = 0.92]), nor was there a significant difference in secondary endpoints.

CONCLUSION

Aprotinin therapy was not associated with a significant reduction in POAF in patients undergoing CTS with CPB. Perioperative transfusion use, LOS, stroke, myocardial infarction, renal failure, graft occlusion, and mortality also did not differ significantly between aprotinin and control groups.

Biomaterial-associated thrombosis: roles of coagulation factors, complement, platelets and leukocytes

Our failure to produce truly non-thrombogenic materials may reflect a failure to fully understand the mechanisms of biomaterial-associated thrombosis. The community has focused on minimizing coagulation or minimizing platelet adhesion and activation. We have infrequently considered the interactions between the two although we are generally familiar with these interactions. However, we have rarely considered in the context of biomaterial-associated thrombosis the other major players in blood: complement and leukocytes. Biomaterials are known agonists of complement and leukocyte activation, but this is frequently studied only in the context of inflammation. For us, thrombosis is a special case of inflammation. Here we summarize current perspectives on all four of these components in thrombosis and with biomaterials and cardiovascular devices. We also briefly highlight a few features of biomaterial-associated thrombosis that are not often considered in the biomaterials literature: The importance of tissue factor and the extrinsic coagulation system. Complement activation as a prelude to platelet activation and its role in thrombosis. The role of leukocytes in thrombin formation. The differing time scales of these contributions.

Neurologic Injury Associated with CABG Surgery: Outcomes, Mechanisms, and Opportunities for Improvement

Neurologic injuries, whether subtle or overt, are a major source of morbidity secondary to coronary artery bypass graft (CABG) surgery. A comprehensive review of research in the area of neurologic injury is provided. We conclude this article by providing insight regarding areas requiring further investigation in order to reduce sustainably the risk of these iatrogenic events among patient undergoing CABG surgery.

Hemodilution During Cardiopulmonary Bypass Increases Cerebral Infarct Volume After Middle Cerebral Artery Occlusion in Rats

Although the optimal hematocrit during cardiopulmonary bypass (CPB) is not defined, excessive hemodilution may lead to organ ischemia via a reduction in oxygen-carrying capacity uncompensated by autoregulatory and/or rheologic increases in organ blood flow. As a result, the consequences of hemodilution in patients at risk for cerebral ischemia are not clearly understood. We designed this study to evaluate the effects of hemodilution in the setting of focal cerebral ischemia during CPB. Wistar rats surgically prepared for CPB were randomized to either hemodilution (hemoglobin (Hb), 6 g/dL; n = 9) or control (Hb, 11 g/dL; n = 8) groups and subsequently exposed to focal cerebral ischemia induced by middle cerebral artery occlusion (MCAO). Immediately after the onset of MCAO (maintained for 90 min), 65 min of hypothermic (28 degrees C) CPB was initiated. Twenty-four hours later, functional neurological outcome and cerebral infarct volume were determined. Compared with controls, the hemodilution group had worse neurological performance (new score = 8 [2], hemodilution; versus 10 [2], control; P = 0.030) and larger total cerebral infarct volumes (182 +/- 84 mm(3), hemodilution; versus 103 +/- 58 mm(3), control; P = 0.043). In this experimental model of CPB with reversible MCAO-induced focal cerebral ischemia, hemodilution worsened neurological function and increased cerebral infarct volume.

Single-ventricle physiology: perioperative implications

Neonates with functional single ventricles have pulmonary and systemic circulations that are supplied in parallel, creating significant cyanosis and ventricular volume overload. The goal of palliative surgery, excluding transplantation, is to convert single-ventricle circulation from a parallel to a series arrangement. This will ultimately require a complete cavopulmonary anastomosis (Fontan-type procedure) in which vena caval blood is rerouted directly into the pulmonary circulation. Various factors require that this palliation occur in stages. Stage I surgery, which is often a Norwood procedure, is done in the neonatal period and stabilizes, but does not resolve, parallel circulation. The tenuous balance between pulmonary and systemic perfusion during this stage makes noncardiac surgery hazardous, and it should be restricted to urgent or emergent indications. Stage II surgery, or partial cavopulmonary anastomosis, relieves both parallel circulation and volume overload, but not cyanosis. Relatively stable hemodynamics during this stage create favorable conditions for elective surgery. Patients who have undergone stage III surgery, the Fontan-type repair, vary in age from toddlers to adults, and in physical status from well-compensated to significantly debilitated. Fontan patients require thorough preoperative assessment when elective surgery is contemplated. Optimal communication between surgeons, anesthesiologists, and cardiologists is essential when caring for the patient with single-ventricle physiology.

Current status of antifibrinolytics in cardiopulmonary bypass and elective deep hypothermic circulatory arrest

Cardiopulmonary bypass (CPB) results in many physiologic derangements, including activation of the hemostatic and fibrinolytic pathways. Deep hypothermic circulatory arrest (DHCA) adds a further insult to the coagulation systems because it involves more extreme hypothermia and organ ischemia related to blood stasis. The abnormalities induced by CPB disrupt the checks and balances in the hemostatic and fibrinolytic systems, resulting in a pathologic state that leads to excessive bleeding and other perioperative complications. Prophylactic antifibrinolytic therapy can attenuate the response to this insult by restoring the delicate balance within these systems, potentially reducing the complication rate and improving patient outcomes.

Aprotinin reduces operative closure time and blood product use after pediatric bypass

BACKGROUND

The use of aprotinin in children undergoing cardiopulmonary bypass is controversial. We hypothesized that aprotinin would reduce blood product use and operative closure time in selected pediatric patients.

METHODS

For a 6-month period starting in October 1999, consecutive cardiopulmonary bypass patients 6 months of age or less (n = 18) or having a repeat sternotomy (n = 18) received aprotinin. Similar consecutive patients from the preceding 6 months served as controls (n = 35 and 41, respectively). Data extracted from medical records included preoperative clinical characteristics, operative and postoperative procedures, and total blood product use.

RESULTS

Patients in the aprotinin and control groups were well matched with regard to preoperative and intraoperative variables. Patients 6 months of age or less who received aprotinin required less operative closure time when compared with controls (median, 93 vs 127 minutes, p = 0.004), and trended toward requiring fewer red blood cell unit exposures (median, three vs five exposures, p = 0.07). Patients undergoing repeat sternotomy who received aprotinin required less operative closure time when compared with controls (mean, 126 vs 159 minutes, p = 0.007), fewer red blood cell unit exposures (median three vs four exposures, p = 0.002), and fewer fresh-frozen plasma unit exposures (median, zero vs one exposure, p = 0.007).

CONCLUSIONS

Aprotinin reduced operative closure time and blood product exposure in pediatric patients undergoing cardiopulmonary bypass who were 6 months of age or less or underwent a repeat sternotomy.

Does aprotinin influence the inflammatory response to cardiopulmonary bypass in patients?

OBJECTIVES

Aprotinin has been shown to have anti-inflammatory properties, but its effects on the inflammatory reaction to cardiopulmonary bypass remain controversial. This prospective, randomized, double-blind study evaluated the influence of aprotinin on various blood markers of inflammation during and after cardiopulmonary bypass.

METHODS

Sixty male patients underwent coronary artery bypass grafting. The patients were randomized into 3 groups: a placebo group, a second group receiving 2,000,000 KIU of aprotinin followed by an infusion of 500,000 KIU/h and 2,000,000 KIU in the pump prime, and a third group receiving half this dosage. Measurements of tumor necrosis factor, interleukin 6, interleukin 8, interleukin 10, endotoxin, histamine, complement factors, prekallikrein, and prostaglandin D(2) were obtained at baseline, 30 minutes after study drug loading, 10 minutes after the beginning of cardiopulmonary bypass, before the end of bypass, 4 hours after bypass, and on the first and second postoperative days.

RESULTS

Aprotinin had no significant effect on any of these parameters. As expected, aprotinin reduced early blood loss in both treated groups.

CONCLUSIONS

These results indicate that aprotinin at doses currently used to reduce blood loss has no significant influence on the systemic inflammatory response during moderate hypothermic cardiopulmonary bypass in human subjects, as assessed by the mediators measured in this study.

Improved Survival of Patients Undergoing Palliation of Hypoplastic Left Heart Syndrome: Lessons Learned From 115 Consecutive Patients

Background Outcome of stage 1 palliation (S1P) for hypoplastic left heart syndrome (HLHS) has improved coincident with application of treatment strategies including continuous superior vena cava oximetry (SvO 2 ), phenoxybenzamine (POB), strategies to minimize the duration of deep hypothermic circulatory arrest (DHCA) and efforts to ameliorate the inflammatory response to cardiopulmonary bypass (CPB) using aprotinin and modified ultrafiltration.

Methods and Results Analysis of a consecutive series of 115 patients undergoing S1P was done to identify the risk factors for mortality and the impact of new treatment strategies. For the current era, July 1996 to October 2001, hospital survival was 93% (75/81) compared with 53% (18/34) for the time period, January 1992 to June 1996, P <0.001. Survival to stage 2 palliation (S2P) was also significantly improved in the current era, 81% (66/81) versus 44% (15/34), P <0.01. Anti-inflammatory treatment strategies demonstrated improved survival by univariate analysis ( P <0.001). Multivariate analysis identified continuous SvO 2 monitoring as a factor favoring S1P survival ( P =0.02) and use of POB as a factor favoring survival to S2P ( P =0.003). In the current era shorter duration of DHCA was associated with improved survival to S2P ( P =0.02).

Conclusions–Improved survival following S1P can be achieved with strategies that allow for early identification of decreased systemic output and the use of afterload reduction to stabilize systemic vascular resistance and therefore the pulmonary to systemic flow ratio. Strategies to ameliorate the inflammatory response to CPB may decrease the degree and duration of postoperative support. Strategies to minimize duration of DHCA may improve intermediate survival and merit additional studies.

Differential effects of aprotinin and tranexamic acid on endotoxin desensitization of blood cells induced by circulation through an isolated extracorporeal circuit

OBJECTIVE

To compare the effects of aprotinin and tranexamic acid on blood cytokine secretion induced by the circulation of blood through an isolated extracorporeal circuit.

DESIGN

Prospective, placebo-controlled study.

SETTING

University hospital.

PARTICIPANTS

Healthy volunteers (n = 18).

INTERVENTIONS

Blood (400 mL) first was drawn from volunteers, then circulated through an isolated extracorporeal circuit. Three groups were compared depending on the addition or not of an antifibrinolytic agent in the circuit (control group [n = 8], tranexamic group [n = 5], aprotinin group [n = 5]). Samples for measurement were taken before and at different time points after the start of circulation through the extracorporeal circuit. Cytokine (tumor necrosis factor-alpha, interleukin [IL]-6, IL-8, and IL-10) concentrations in the plasma and in the supernatant of lipopolysaccharide-stimulated whole blood cell cultures were analyzed.

MEASUREMENTS AND MAIN RESULTS

In the control and tranexamic acid groups, tumor necrosis factor-alpha, IL-6, and IL-10 secretion by whole blood cell cultures were rapidly decreased, whereas IL-8 secretion was unaffected. In the aprotinin group, IL-8 secretion was also decreased (p < 0.05).

CONCLUSION

These results show that aprotinin, but not tranexamic acid, modulates the inflammatory response by reducing the IL-8 secretion of blood cells activated by contact with foreign surfaces.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Heparin-bonded cardiopulmonary bypass circuits reduce cognitive dysfunction

OBJECTIVE

To determine the incidence of cerebral dysfunction in cardiac surgical patients exposed to heparin-bonded cardiopulmonary bypass (HB-CPB) versus nonheparin-bonded cardiopulmonary bypass (NH-CPB) circuits through neuropsychometric testing and to correlate these findings with markers of the systemic inflammatory response to CPB.

DESIGN

Prospective, randomized, blinded clinical trial.

SETTING

University hospital.

PARTICIPANTS

Sixty-one patients undergoing elective cardiac surgery.

INTERVENTIONS

A cohort of 61 patients scheduled for elective coronary artery bypass graft surgery were prospectively randomized to receive either HB-CPB or NH-CPB circuits during surgery. Patients were evaluated for cerebral injury using a battery of neuropsychometric tests at the following 3 time points: (1) before surgery as a baseline examination, (2) postoperative day 5, and (3) postoperative week 6. Blood samples were drawn to measure inflammatory markers at the following time points: (1) preincision, after induction of anesthesia, (2) 15 minutes after onset of CPB, (3) 30 minutes after CPB, (4) 6 hours postoperatively, and (5) 24 hours postoperatively.

MEASUREMENTS AND MAIN RESULTS

Neuropsychometric performance was evaluated by group-rate and event-rate analyses. By group-rate analysis, patients undergoing surgery with HB-CPB performed significantly better at 5 days after surgery on 2 neuropsychometric tests (trails A [p < 0.01] and finger tapping with the dominant hand [p < 0.01]) and at 6 weeks after surgery on one neuropsychometric test (trails A [p < 0.01]). By event-rate analysis, at 5 days, patients undergoing surgery with HB-CPB circuits had less cognitive dysfunction (p < 0.05) compared with patients undergoing surgery with NH-CPB circuits. Serum samples were analyzed to evaluate markers of complement activation (C3a), proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6), and coagulation (thrombin-antithrombin complex [TAT]) using the quantitative sandwich enzyme immunoassay technique. Although there were no significant differences in cytokine activation in either group, C3a was significantly higher in the NH-CPB group intraoperatively at 1 hour after CPB (p < 0.05), and TAT was higher in the HB-CPB group at 24 hours after surgery (p < 0.05).

CONCLUSIONS

Patients undergoing cardiac surgery with CPB have less postoperative cognitive dysfunction during CPB when HB-CPB circuits are employed. Although there was a relationship, this finding did not correlate with decreased complement activation intraoperatively and activation of coagulation postoperatively.

Postoperative hyperthermia is associated with cognitive dysfunction after coronary artery bypass graft surgery

BACKGROUND AND PURPOSE

Temperature is a well-known modulator of experimental cerebral injury. We hypothesized that hyperthermia would be associated with a worsened cognitive outcome after coronary artery bypass graft surgery (CABG).

METHODS

Three hundred consenting patients undergoing cardiopulmonary bypass for CABG had hourly postoperative temperatures recorded. The degree of postoperative hyperthermia was determined by using the maximum temperature within the first 24 hours as well as by calculating the area under the curve for temperatures >37 degrees C. Patients underwent a battery of cognitive testing both before surgery and 6 weeks after surgery. By use of factor analysis, 4 cognitive domains (scores) were identified, and the mean of the 4 scores was used to calculate the cognitive index (CI). Cognitive change was calculated as the 6-week CI minus the baseline CI. Multivariable linear regression (controlling for age, baseline cognitive function, and temperature during cardiopulmonary bypass) was used to compare postoperative hyperthermia with the postoperative cognitive change.

RESULTS

The maximum temperature within the first 24 hours after CABG ranged from 37.2 degrees C to 39.3 degrees C. There was no relationship between area under the curve for temperatures >37 degrees C and cognitive dysfunction (P=0.45). However, the maximum postoperative temperature was associated with a greater amount of cognitive dysfunction at 6 weeks (P=0.05).

CONCLUSIONS

This is the first report relating postoperative hyperthermia to cognitive dysfunction after cardiac surgery. Whether the hyperthermia caused the worsened outcome or whether processes that resulted in the worsened cognitive outcome also produced hyperthermia requires further investigation. In addition, interventions to avoid postoperative hyperthermia may be warranted to improve cerebral outcome after cardiac surgery.

Attenuation of neurologic injury during cardiac surgery

Neurologic injury after cardiac surgery can be divided into type I, including clinically apparent stroke, seizures stupor, or coma, and much more occurring type II injury, including intellectual deterioration, memory deficit, or seizures. Cerebral embolization is demonstrably etiologic in many such cases, and several new aortic cannulas are being introduced that are aimed at capturing or diverting potential cerebral emboli. No outcome data are yet available. Several potentially cerebroprotective pharmacologic therapies including thiopental, propofol, and nimodipine, have been assessed clinically but, generally, the results have been poor. Meta-analysis of the large North American aprotinin database of prospective, randomized, placebo-controlled clinical trials is suggestive of a cerebroprotective potential associated with high-dose aprotinin administration.

Some inflammation-related parameters in patients following normo- and hypothermic cardio-pulmonary bypass

AIMS

One of the complications of Cardio-Pulmonary Bypass is the Systemic Inflammatory Response Syndrome. Cardio-Pulmonary Bypass can be performed under either normothermic or hypothermic conditions. The aim of this study was to compare some inflammation-related parameters of patients following normothermic and hypothermic bypass. Moreover, attempts were undertaken to detect endotoxin, an inflammatory agent that has been implicated in the Systemic Inflammatory Response Syndrome, in the serum of patients. Levels of serum anti-endotoxin antibodies were estimated since they have been reported to negate the effect of endotoxin in the inflammatory syndrome.

METHODS AND RESULTS

Seventeen normothermic and 20 hypothermic cases were studied. Blood specimens were collected pre-, off- and post-bypass. Pertinent clinical and surgical data were collected. Hematological parameters (leukocyte, neutrophil and platelet counts) and liver function tests were determined by standard procedures. Endotoxin was determined by the Limulus Lysate Assay and anti-endotoxin antibodies by an enzyme immunoassay. Complement (C3 and C4) levels were determined by radial immunodiffusion. There were increases in leukocyte and neutrophil, and a decline in platelet numbers in both groups of patients. There was a decline in C3 and C4 levels in both groups of patients. Endotoxin was not detected in sera, and anti-endotoxin antibody levels were similar, in both groups of patients.

CONCLUSION

There were no significant differences in most of the altered inflammation-related parameters between the two groups of patients. Some of the findings might be partly due to hemo-dilution. The hydrophobic nature of endotoxin among other factors, might have hindered its detection in serum.

Aprotinin and the systemic inflammatory response after cardiopulmonary bypass

Cardiopulmonary bypass is associated with a systemic inflammatory response, a spectrum of pathophysiologic changes ranging from mild organ dysfunction to multisystem organ failure. Complications include coagulation disorders (bleeding diathesis, hyperfibrinolysis) from platelet defects and plasmin activation, as well as pulmonary dysfunction from neutrophil sequestration and degranulation. Diverse injuries are a consequence of multiple inflammatory mediators (complement, kinins, kallikrein, cytokines). Both plasmin and kallikrein amplify the inflammatory response by activating components of the contact activation system. The full-Hammersmith (high dose) of aprotinin, a serine protease inhibitor approved for reducing blood loss and transfusion requirements in cardiopulmonary bypass, inhibits kallikrein and plasmin, resulting in suppression of multiple systems involved in the inflammatory response. Specifically, inhibition of factor XII, bradykinin, C5a, neutrophil integrin expression, elastase activity, and airway nitric oxide production are observed. Clinical correlates include reduced capillary leak, preserved systemic vascular resistance and blood pressure, and improved myocardial recovery following ischemia. Overall, evidence indicates that aprotinin attenuates the systemic inflammatory response associated with cardiopulmonary bypass.

Comparison of tumor necrosis factor-alpha effect on the expression of iNOS in macrophage and cardiac myocytes

Proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), are elevated during cardiopulmonary bypass (CPB), heart failure, and inflammatory cardiac and systemic diseases. Elevated TNF-alpha has been linked to diminished cardiac function, decreased systemic vascular resistance, as well as renal and pulmonary dysfunction. It is understood that myocardial tissues can express TNF-alpha, which results in the induction of inducible nitric oxide synthase (iNOS) leading to a significant decline in cardiac function and other direct effects. The hypothesis of this study was to determine if TNF-alpha would stimulate iNOS and its product nitric oxide (NO) similarly in immortalized macrophage and cardiac myocytes. Cultured macrophages (RAW 264.7) and cardiac myocytes (HL-1) were placed into two treatment groups and a control. The treatments included: (1) TNF-alpha and lipopolysaccharide (LPS); and (2) LPS, TNF-alpha, interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) incubated for 8 h. The macrophage expression of iNOS increased by 365% (p < 0.01) and its product, NO, increased proportionally. The expression of iNOS in the cardiac myocyte did not increase with TNF-alpha and LPS. However, with the addition of IFN-alpha and IL-1beta iNOS increased to 140% of control (p < 0.05). Myocyte cGMP and NO did not increase significantly with TNF-alpha treatment. This study suggests that HL-1 myocyte iNOS cannot be induced by TNF-alpha, unlike macrophage iNOS. Furthermore, the resultant cardiac dysfunction, secondary to proinflammatory cytokines effects, is regulated via diverse pathways.

Cytokine release and neutrophil activation are not prevented by heparin-coated circuits and aprotinin administration

BACKGROUND

Cardiopulmonary bypass (CPB) initiates a whole-body inflammatory response where complement and neutrophil activation and cytokine release play an important role. This prospective trial examined the effects of both heparin-coated circuits and aprotinin on the inflammatory processes during CPB, with respect to cytokine release and neutrophil activation.

METHODS

Two hundred patients undergoing cardiac surgery were randomized in four groups of 50 patients each: heparin-coated circuit with aprotinin (HCO-A) or without aprotinin (HCO) administration, and uncoated circuit with aprotinin (C-A) or without aprotinin administration (C). In groups receiving aprotinin, a high-dose regimen was given. In all groups, high initial doses of heparin were used (3 mg/kg intravenously). Tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and IL-8, and myeloperoxidase and elastase levels were measured in plasma samples taken before, during, and after CPB.

RESULTS

In all groups, the TNF-alpha, IL-6, and IL-8 levels reached a maximum after protamine administration. After 24 hours, they remained significantly elevated (IL-6 and IL-8) or returned to baseline values (TNF-alpha). A similar pattern was observed with myeloperoxidase and elastase levels. No significant intergroup differences were observed.

CONCLUSIONS

CPB is associated with cytokine release and neutrophil activation, which are not attenuated by the use of heparin-coated circuits or by the administration of aprotinin. Aprotinin and heparin-coated circuits do not show additive effects.

Neurophysiologic monitoring and outcomes in cardiovascular surgery

The first step to make in improving neurologic outcome is to recognize and accept neurologic injury occurs in all patient groups undergoing CPB. Fortunately, that stage has now been passed. Accurate detection and documentation of the incidence of brain injury is the next progression. At the same time, the cause of the injury needs to be established. Since the introduction of CPB, numerous improvements and refinements have been achieved, making it the acceptable, everyday clinical tool that has enabled the development of cardiac surgery. Despite these improvements, CPB-related morbidity persists. The advent of new technologic advances drives the quest for new techniques. New protective strategies for many end organs, including the heart, kidney, and brain, are evolving. No organ system should be viewed in isolation; otherwise, organ-specific protective strategies may arise in conflict. A strategy that confers absolute myocardial protection would be ideal, but at what cost to the protection of the kidneys, intestines, and brain? A neuroprotective strategy would ideally eliminate brain injury and be beneficial for all organs. The only way to continue to make progress is by the scientific evaluation of new techniques. The use of appropriate monitoring and outcome measures is fundamental to this process.

The effects of aprotinin on outcome from cerebral ischemia in the rat

The administration of aprotinin has been associated with a reduction in cardiac surgery-related stroke. Intrinsic neuroprotective properties of this drug have not been evaluated in laboratory outcome models of cerebral ischemia. The purpose of this study was to determine whether aprotinin exhibits neuroprotective effects against either global or focal cerebral ischemia in the rat. Fasted rats were administered aprotinin (30,000 or 60,000 KIU/kg) or vehicle (0.9% NaCl) IV before global ischemia (10 min bilateral carotid occlusion with mean arterial pressure 30 mm Hg) or focal ischemia (75 min of transient middle cerebral artery occlusion [MCAO]). Five days after global ischemia, the percentage of dead hippocampal CA1 neurons (mean +/- SD) was similar among the groups (small-dose aprotinin: 49+/-31, n = 15; large-dose aprotinin: 55+/-31, n = 13; vehicle: 47+/-31, n = 16; P = 0.74). After 7 days' recovery from MCAO, no difference among the groups was observed for either neurologic score (P = 0.99) or cerebral infarct volume (small-dose aprotinin: 136+/-80 mm3, n = 23; large-dose aprotinin: 132+/-101 mm3, n = 11; vehicle: 121+/-81 mm3, n = 21; P = 0.87).

IMPLICATIONS

Aprotinin offers no neuroprotection against either global or focal cerebral ischemia in the rat when administered as a single preischemic bolus.

Modifying risk for extracorporeal circulation: trial of four antiinflammatory strategies

BACKGROUND

Despite recent rediscovery of beating heart cardiac surgical techniques, extracorporeal circulation remains appropriate for most heart operations. To minimize deleterious effects of cardiopulmonary bypass, antiinflammatory strategies have evolved.

METHODS

Four state-of-the-art strategies were studied in a prospective, randomized, preoperatively risk stratified, 400-patient study comprising primary (n = 358), reoperative (n = 42), coronary (n = 307), valve (n = 27), ascending aortic (n = 9), and combined operations (n = 23). Groups were as follows: standard, roller pump, membrane oxygenator, methylprednisolone (n = 112); aprotinin, standard plus aprotinin (n = 109); leukocyte depletion, standard plus a leukocyte filtration strategy (n = 112); and heparin-bonded circuitry, centrifugal pumping with surface modification (n = 67).

RESULTS

Analysis of variance, linear and logistic regression, and Pearson correlation were applied. Actual mortality (2.3%) was less than half the risk stratification predicted mortality (5.7%). The treatment strategies effectively attenuated markers of the inflammatory response to extracorporeal circulation. Compared with the other groups the heparin-bonded circuit had highly significantly decreased complement activation (p = 0.00001), leukocyte filtration blunted postpump leukocytosis (p = 0.043), and the aprotinin group had less fibrinolysis (p = 0.011). Primary end points, length of stay, and hospital charges, were positively correlated with operation type, age, pump time, body surface area, stroke, pulmonary sequelae, predicted risk for stroke, predicted risk for mortality, and risk strata/treatment group interaction (p = 0.0001). In low-risk patients, leukocyte filtration reduced length of stay by 1 day (p = 0.02) and mean charges by $2,000 to $6,000 (p = 0.05). For high-risk patients, aprotinin reduced mean length of stay up to 10 fewer days (p = 0.02) and mean charges by $6,000 to $48,000 (p = 0.0007).

CONCLUSIONS

These pharmacologic and mechanical strategies significantly attenuated the inflammatory response to extracorporeal circulation. This translated variably into improved patient outcomes. The increased cost of treatment was offset for selected strategies through the added value of significantly reduced risk.