Effects of simulated extracorporeal circulation on human leukocyte elastase release, superoxide generation, and procoagulant activity

Current Understanding of Leukocyte Phenotypic and Functional Modulation During Extracorporeal Membrane Oxygenation: A Narrative Review

A plethora of leukocyte modulations have been reported in critically ill patients. Critical illnesses such as acute respiratory distress syndrome and cardiogenic shock, which potentially require extracorporeal membrane oxygenation (ECMO) support, are associated with changes in leukocyte numbers, phenotype, and functions. The changes observed in these illnesses could be compounded by exposure of blood to the non-endothelialized surfaces and non-physiological conditions of ECMO. This can result in further leukocyte activation, increased platelet-leukocyte interplay, pro-inflammatory and pro-coagulant state, alongside features of immunosuppression. However, the effects of ECMO on leukocytes, in particular their phenotypic and functional signatures, remain largely overlooked, including whether these changes have attributable mortality and morbidity. The aim of our narrative review is to highlight the importance of studying leukocyte signatures to better understand the development of complications associated with ECMO. Increased knowledge and appreciation of their probable role in ECMO-related adverse events may assist in guiding the design and establishment of targeted preventative actions.

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.

Perflubron emulsion reduces inflammation during extracorporeal circulation

The recovery from cardiac surgery and cardiopulmonary bypass can be complicated by an acute inflammatory response. Circulating blood through an extracorporeal circuit (ECC) contributes to this complication. Perfluorocarbon-based blood substitutes (PFCs) are under investigation for use as a component of the ECC "prime" solution, because PFCs increase the oxygen-carrying capacity of the diluted blood. Some PFCs may provide the additional benefit of attenuating the ECC-induced inflammatory response. Earlier, we reported that perflubron emulsion (PFE, Alliance Pharmaceutical Corp.) reduced neutrophil (PMN) activation in vivo. However, the potential of PFE to reduce ECC-induced PMN activation has not been investigated. In this study, we used a small-scale ECC model to quantify the extent of PMN activation during circulation and to examine if PFE treatment attenuated PMN activation. ECC circuits were filled with a mixture of blood and Plasmalyte. Two groups were studied: an untreated group containing blood plus PlasmaLyte and a treated group in which some of the Plasmalyte was substituted with PFE (4.5 g/100 ml). Hematology and measures of whole blood PMN activation were made from blood samples taken periodically throughout the 120-min ECC circulation period. We found, for the untreated group, a significant decrease in the number of circulating PMNs and an increase in PMN activation with time. PMN activation was demonstrated as a significant increase in the expression of the PMN adhesion protein CD11b (P < 0.05) and an increase in PMN oxygen free radical production (reactive oxygen species (ROS)). After 120 min of circulation, the PMNs remained capable of a significant response to a second inflammatory stimulus, but PFE treatment significantly attenuated the fMLP-induced increase in PMN ROS at t = 120 min (P < 0.05). These results suggest that PFE may have dual utility in cardiac surgery, to increase oxygen delivery and to serve as an antiinflammatory agent.

Effect of a leukocyte-depleting filter in an extracorporeal circuit used for low-flow ischemia and reperfusion of equine jejunum

OBJECTIVE

To determine effect of leukocyte depletion on hematologic, morphologic, and metabolic variables of equine jejunum after induction of arterial low-flow ischemia and reperfusion by use of an extracorporeal circuit.

ANIMALS

14 healthy adult horses.

PROCEDURE

A segment of jejunum was surgically removed and maintained in an isolated circuit for 3 hours (control group), arterial flow was reduced to 20% of baseline for 40 minutes followed by 1 hour of reperfusion (low-flow group), or leukocyte depletion was filter-induced, and low-flow ischemia and reperfusion were conducted as in the low-flow control group (filter-treated group). Various metabolic, hemodynamic, and histomorphologic variables were evaluated, including effects of electrical field stimulation and L-N-nitro-arginine-methyl-ester (L-NAME) on contractile activity.

RESULTS

The extracorporeal circuit appeared to maintain the jejunum within physiologic limits for an extended period. Low-flow ischemia with reperfusion induced significant differences in various measurements, compared with control specimens. Significant differences were not detected between the low-flow and filter-treated groups. Myeloperoxidase activity was greater in the low-flow group than the control group, whereas a difference was not detected between control and filter-treated groups.

CONCLUSIONS AND CLINICAL RELEVANCE

The extracorporeal circuit maintained intestine for 3 hours in a physiologic state and may be used for simulation of tissue injury. Leukocyte depletion generally did not attenuate the effects of low-flow ischemia and reperfusion on equine small intestine.

Use of an extracorporeal circuit to evaluate effects of ischemia and reperfusion of the equine large colon

OBJECTIVE

To determine efficacy of an extracorporeal circuit to maintain a segment of equine large colon for 3.5 hours and to evaluate the effect of low arterial flow on histologic and metabolic variables.

SAMPLE POPULATION

Segments of large colon from 15 healthy adult horses.

PROCEDURE

The pelvic flexure was surgically removed and maintained in an isolated circuit. In the control group, tissue was evaluated for 3.5 hours, whereas in the low-flow group, arterial flow was reduced to 20% of baseline for 40 minutes followed by 2 hours of reperfusion. Various metabolic and hemodynamic variables were evaluated at 30-minute intervals. Effects of nitric oxide (NO) and L-N-nitro-arginine-methyl-ester (L-NAME) on contractile activity were determined, and histomorphologic evaluation was performed at the completion of the study.

RESULTS

Low-flow ischemia with reperfusion caused significant histomorphologic differences, compared with the control group. In the low-flow group, significant differences included reduction in PaCO2, reduction in bicarbonate concentrations, increase in PaO2, and an increase in base deficit in arterial and venous blood samples. Other significant differences included increases in PCV, protein concentration, total WBC count, and albumin clearance for the low-flow group. Differences were not detected in inhibitory activity of the low-flow group relative to the control tissue with or without addition of NO and L-NAME.

CONCLUSION

The extracorporeal circuit maintained a segment of equine intestine for 3.5 hours and can be used to simulate ischemic injury. The extracorporeal circuit provides the potential to investigate pharmaceutic agents that can minimize intestinal injury.

Quality assessment of heparin coatings by their binding capacities of coagulation and complement enzymes

In vitro testing of blood contacting materials before clinical application is generally advisable. Four heparin coatings from different manufacturers were tested for adsorbed proteins and soluble activation markers. The surface with the highest antithrombin, thrombin, high-molecular-weight-kininogen (HMWK) and the lowest fibrinogen binding capacity (Carmeda, Medtronic) showed significantly lower levels of granulocytes and platelet activation (beta-TG, PMN-elastase release). No statistically significant differences in soluble markers of the coagulation system could be detected (F1 + 2, TAT). Interestingly, complement activation (TCC) was significantly reduced within the group of the lowest adsorption of the complement factor C3. Our data demonstrate that there is a relation between the binding affinity of proteins (C1-inhibitor, C3-complement) and the consecutive changes in complement activation (TCC). Therefore, measuring adsorbed proteins on artificial surfaces is a suitable, sensitive and very reproducible method for assessing the thrombogenicity of biomaterials.

Effects of selectin-sialyl Lewis blockade on mesenteric microvascular permeability associated with cardiopulmonary bypass

OBJECTIVES

Cardiopulmonary bypass is associated with an inflammatory response that is associated with a neutrophil-mediated microvascular barrier injury. We studied the effects of blocking neutrophil-endothelial tethering on microvascular permeability and edema formation during cardiopulmonary bypass. Using a selectin antagonist that prevents interactions with their ligands, we hypothesized that there would be less neutrophil infiltration into the tissue and a reduction in microvascular permeability and edema formation.

METHODS

A canine mesenteric lymphatic fistula was created to measure Starling forces and to determine microvascular permeability. Normothermic, atrial-femoral cardiopulmonary bypass was initiated (70-90 mL. kg(-1). min(-1)). Intestinal tissue water was determined with microgravimetry. Ileal tissue myeloperoxidase was measured as an index of neutrophil tissue infiltration. One experimental group received the selectin antagonist TBC 1269 before the initiation of bypass, and the control group received saline solution.

RESULTS

There was a modest increase in microvascular permeability in both groups, as evidenced by significantly increased transvascular protein clearance and a trend toward a decrease in reflection coefficient. There were no differences in the experimental group compared with the control group. Ileal tissue myeloperoxidase levels were lower in the experimental group than in the control group.

CONCLUSIONS

The selectin antagonist TBC 1269 reduces neutrophil infiltration into the ileum without altering ileal microvascular permeability or edema associated with cardiopulmonary bypass.

Pulmonary artery perfusion with protective solution reduces lung injury after cardiopulmonary bypass

BACKGROUND

The inflammatory response and higher temperature of lung tissue during cardiopulmonary bypass can result in lung injury. This study was to evaluate the protective effect of pulmonary perfusion with hypothermic antiinflammatory solution on lung function after cardiopulmonary bypass.

METHODS

Twelve adult mongrel dogs were randomly divided into two groups. The procedure was carried out through a midline sternotomy, cardiopulmonary bypass was established using cannulas placed in the ascending aorta, superior vena cava, and right atrium near the entrance of the inferior vena cava. After the ascending aorta was clamped and cardioplegic solution infused, the right lung was perfused through a cannula placed in the right pulmonary artery with 4 degrees C lactated Ringer's solution in the control group (n = 6) and with 4 degrees C protective solution in the antiinflammation group (n = 6). Antiinflammatory solution consisted of anisodamine, L-arginine, aprotinin, glucose-insulin-potassium, and phosphate buffer. Plasma malondialdehyde, white blood cell counts, and lung function were measured at different time point before and after cardiopulmonary bypass; lung biopsies were also taken.

RESULTS

Peak airway pressure increased dramatically in the control group after cardiopulmonary bypass when compared with the antiinflammation group at four different time points (24 +/- 1, 25 +/- 2, 26 +/- 2, 27 +/- 2 cm H2O versus 17 +/- 2, 18 +/- 1, 17 +/- 1, 18 +/- 1 cm H2O; all p < 0.01). Pulmonary vascular resistance increased significantly in the control group than in the antiinflammation group at 5 and 60 minutes after cardiopulmonary bypass (1,282 +/- 62 dynes x s x cm(-5) versus 845 +/- 86 dynes x s x cm(-5) and 1,269 +/- 124 dynes x s x cm(-5) versus 852 +/- 149 dynes x s x cm(-5), p < 0.05). Right pulmonary venous oxygen tension (PvO2) in the antiinflammation group was higher than in the control group at 60 minutes after cardiopulmonary bypass (628 +/- 33.3 mm Hg versus 393 +/- 85.9 mm Hg, p < 0.05). The ratio of white blood cells in the right atrial and the right pulmonary venous blood was lower in the antiinflammation group than in the control group at 5 minutes after the clamp was removed (p < 0.05). Malondialdehyde were lower in the antiinflammation group at 5 and 90 minutes after the clamp was removed (p < 0.01 and p < 0.05, respectively). Histologic examination revealed that the left lung from both groups had marked intraalveolar edema and abundant intraalveolar neutrophils, whereas the right lung in the control group showed moderate injury and the antiinflammation group had normal pulmonary parenchyma.

CONCLUSIONS

Pulmonary artery perfusion using hypothermic protective solution can reduce lung injury after cardiopulmonary bypass.

Enhanced responsiveness of circulatory neutrophils after cardiopulmonary bypass: increased aggregability and superoxide producing capacity

Cardiac surgery with cardiopulmonary bypass (CPB) induces a whole body inflammatory response that sometimes leads to postoperative organ dysfunction, and neutrophil activation plays an important role in this reaction. Neutrophil priming has been described as a change in neutrophil status such that neutrophils show enhanced responsiveness to a second activating stimulus. We hypothesized that neutrophil priming occurs by cardiac surgery with CPB and is temporally related to the neutrophilia after surgery. To evaluate primed circulatory neutrophil status, we measured aggregation activity stimulated by N-formyl-methyl-leucyl-phenyl-alanine (FMLP) and free radical producing activity by tumor necrosing factor (TNF) alpha in peripheral blood samples. Eleven adult patients undergoing elective cardiac surgery with CPB were studied. Blood samples were taken before surgery, at the end of bypass, 12 h after surgery, and 7 days after surgery. Aggregation activity and superoxide generation were significantly elevated 12 h after surgery when compared to presurgery values, indicating that cardiac surgery is associated with circulatory neutrophil priming. The number of neutrophils markedly increased at the end of cardiopulmonary bypass and reached a peak 12 h after surgery. The circulatory neutrophils of cardiac surgical patients become primed after surgery, coincident with the peak neutrophil count. These results suggest that circulatory neutrophils after cardiac surgery with CPB have enhanced responsiveness and are predisposed to systemic inflammation.

Acute phase and opsonin response in cardiac surgery patients: influence of underlying cardiac disease

Cardiopulmonary bypass (CPB) leads to an activation of plasma cascade systems, complement activation, and an acute phase response. To evaluate the influence of the underlying cardiac disease on the activation pattern of these systems, we compared inflammatory changes in coronary artery bypass grafting (CABG) patients with patients undergoing aortic valve replacement. We investigated changes of the acute phase proteins alpha 1-proteinase inhibitor and fibrinogen, the unspecific opsonin fibronectin, and the complement components C3c and C4 induced by extracorporeal circulation in 12 patients undergoing aortic valve replacement and in 12 patients undergoing CABG. Concentrations of C3c and C4 decreased in both groups after the onset of CPB and C4 concentration remained below post-induction levels up to 24 h after onset of CPB (p = 0.04). Fibronectin levels dropped immediately before the onset of CPB (p = 0.01), reaching the lowest values after 20 min of extracorporeal circulation. Fibrinogen and alpha 1-proteinase inhibitor levels after induction of anaesthesia were significantly higher in the CABG group and remained higher throughout the entire study period (p < 0.001). As an indicator of a postoperative acute phase response, concentrations of both proteins rose in the postoperative period above post-induction levels (p < 0.02).

Effects of depletion of leukocytes and platelets on cardiac dysfunction after cardiopulmonary bypass

BACKGROUND

This study examined the effects of the depletion of leukocytes and platelets from circulated blood on cardiac function after cardiopulmonary bypass in 37 patients who underwent coronary artery bypass grafting or aortic valve replacement.

METHODS

Leukocytes and platelets were removed continuously using a blood cell separator, beginning immediately after the start of the operation and ending 1 hour after the release of the aortic cross-clamp in 19 patients (LPD group), but not in the remaining 18 patients (control group). Blood cell counts and levels of thromboxane B2, 6-keto-prostaglandin F1alpha, leukocyte elastase, complements C3a and C4a, thrombin-antithrombin III complex, and D-dimer were determined periodically during and after the operation. The cardiac index, the difference between the central and peripheral core temperatures, and the doses of catecholamines and vasodilators required to support the circulation in the early postoperative period also were assessed.

RESULTS

Leukocyte and platelet counts and levels of leukocyte elastase, thromboxane B2, thromboxane2/6-ketoprostaglandin F1alpha, thrombin-antithrombin III complex, and D-dimer were significantly lower in the LPD group than in the control group before and after the release of the aortic cross-clamp and during the perioperative period. There were no significant differences in the levels of 6-keto-prostaglandin F1alpha or complements C3a and C4a between the two groups. The catecholamine dose was significantly lower in the LPD group than in the control group (1.1 +/- 2.5 versus 5.0 +/- 5.2 mg/kg, respectively). Fewer patients required the use of nitroprusside as a vasodilator in the LPD group than in the control group (1/19 versus 12/18, respectively).

CONCLUSIONS

The depletion of leukocytes and platelets using a blood cell separator prevents the deterioration of cardiac function after cardiac operations using cardiopulmonary bypass.

A human urinary protease inhibitor (ulinastatin) inhibits neutrophil extracellular release of elastase during cardiopulmonary bypass

OBJECTIVES

To determine the benefits of a human urinary protease inhibitor (ulinastatin) on postoperative pulmonary dysfunction associated with neutrophil activation during cardiopulmonary bypass.

DESIGN

A prospective, randomized, clinical study.

SETTING

The study was performed at Keio University Hospital, Tokyo.

PARTICIPANTS

Eighteen adult patients scheduled for primary cardiac surgery.

INTERVENTIONS

The patients were randomly assigned either to the control group (n = 8) or to the group (n = 10) receiving ulinastatin (600,000 U in total).

MEASUREMENTS AND MAIN RESULTS

Human neutrophil ability to release elastase in response to N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) in vitro was measured before and after cardiopulmonary bypass, together with plasma levels of neutrophil elastase complex, interleukin-B, and C3a. Intrapulmonary shunt fraction was then calculated. Neutrophil elastase release in response to fMLP significantly increased in the control group, but remained unchanged in the ulinastatin group. In addition, ulinastatin minimized the increase of plasma neutrophil elastase, independently of the production of interleukin-B or C3a. Simultaneously, ulinastatin ameliorated the increase of intrapulmonary shunt, which was correlated with extracellular elastase release.

CONCLUSIONS

Ulinastatin attenuated the elevation of fMLP-induced elastase release, which was associated with the deterioration of gas exchange during cardiopulmonary bypass. The administration of this agent has a potential to lessen the risk of postperfusion lung injury.

The inflammatory response and extracorporeal circulation

Defining the cause of organ and tissue dysfunction associated with the use of perfusion systems will produce methods of prevention or treatment and improve patient outcome. The problem is the plethora of triggers, effectors, and mediators in this process, which can now be measured. Each new measureable compound becomes another biochemical "smoking gun" without physiological data to show any relevance to the human problem. This review critically compares and contrasts the role of certain, largely novel, initiation, amplification, and cytotoxic mechanisms in the inflammatory response of the myocardium and pulmonary systems after a period of cardiopulmonary bypass. The available evidence strongly points to the process being different for each of these tissue beds. These data suggest that ensuring normal lung and heart functions after surgery will require separate therapeutic strategies.

Mechanical white blood cell damage in rotary blood pumps

Mechanical trauma of white blood cells (WBC) due to the operation of a rotary blood pump was examined, using a simple method of trypan blue dye exclusion test for a cell viability measurement. The degree of WBC trauma was investigated using a roller pump (RP) and 3 commercially available centrifugal pumps (Bio-Medicus [BP], Capiox [CP], Nikkiso [NK]), and compared with the red blood cell (RBC) trauma. Each pump was operated 3 times at a flow rate of 5 L/min against the total pressure head of 350 mm Hg for 6 h in a mock circuit with 400 ml of fresh bovine blood. Blood was sampled at 2 h intervals measuring plasma free hemoglobin concentration and the percentage of damaged WBC in the trypan blue dye exclusion test. Each pump demonstrated a linear increase in the degree of WBC trauma, and there were differences among the tested pumps (RP > BP > CP > NK). These findings were similar to those of the free hemoglobin measurements. To compare the degree of RBC and WBC trauma, the probability (gamma, omega) of RBC and WBC to be damaged was calculated, respectively. gamma = delta DRBC/delta N, omega = delta DWBC/delta N where DRBC and DWBC are the ratios of the damaged RBC and WBC, respectively, and N is the passing number defined as Qt/V (Q, flow rate; t, time; V, circulating volume). The data of this study demonstrated that the omega value was approximately 20 times or more greater than the gamma equally in all the tested pumps. This suggests that a WBC is more vulnerable to mechanical damage by a rotary blood pump than a RBC.

Expression of adhesion and activation molecules on lymphocytes during open-heart surgery with cardiopulmonary bypass

Open-heart surgery with cardiopulmonary bypass (CPB) and abdominal surgery are associated with lymphocytopenia. We measured a panel of adhesion and activation molecules on lymphocytes to clarify possible association of CPB with increased expression of these molecules. Eight patients undergoing open-heart surgery and eight with abdominal surgery were studied. The adhesion molecules CD11a/CD18 (LFA-1_, CD11c/CD18 and CD44 and the activation molecules CD25, CD69, CD71 and MHCII were measured, using monoclonal antibodies and flow cytometry. Lymphocytopenia was observed during CPB and for some hours after both open-heart and abdominal surgery. The proportion of CD11a/CD18-positive lymphocytes rose from 67.6 +/- 8% to 86.4 +/- 3% after aortic declamping (p < 0.05). The expression of activation molecules CD25, CD69 and CD71 was unchanged during and after open-heart as well as abdominal operations. Thus CPB was associated with increased expression of the adhesion molecule CD11a/CD18 on lymphocytes, while the expression of activation molecules on lymphocytes was unchanged.

Complement and neutrophil activation during cardiopulmonary bypass: a randomized comparison of hypothermic and normothermic circulation

OBJECTIVE

Activation of both complement and neutrophils has been demonstrated to be involved in many pathological reactions following cardiopulmonary bypass (CPB). The aim of the present study is to evaluate the effect of normothermic and hypothermic CPB on both complement and neutrophil activation.

METHODS

Two groups of patients (n = 20 each) scheduled for elective coronary artery bypass grafting, underwent CPB with intermittent warm or cold blood cardioplegia. Plasma concentration of C3a, C5a and C5b-9, as well as nitro-blu tetrazolium (NBT) scores of circulating neutrophils were measured before anesthesia, 10 and 30 min after the beginning of CPB, and 8, 16 and 24 h, postoperatively.

RESULTS

In both groups, CPB determined a significant complement activation, evidenced as a significant increase in plasma concentration of C3a, C5a and C5b-9. This in turn triggered the neutrophil activation, documented as a significant increase of NTB scores in circulating neutrophils at the end of CPB and in the early postoperative period. Interestingly, in the warm group the extent of both complement and neutrophil activation was significantly higher compared with the cold group during the whole sampling period.

CONCLUSION

In conclusion, our study clearly demonstrates that warm CPB is associated with an increased ability to activate complement and neutrophils in patients undergoing coronary surgery.

Effects of inhibition of complement activation using recombinant soluble complement receptor 1 on neutrophil CD11b/CD18 and L-selectin expression and release of interleukin-8 and elastase in simulated cardiopulmonary bypass

The inflammatory response to cardiopulmonary bypass includes activation of complement and induction of several neutrophil activation pathways. A recombinant soluble form of complement receptor 1 was used as a specific inhibitor of complement activation in simulated cardiopulmonary bypass circuits. Substantial complement activation was observed in these circuits with progressive accumulation of both plasma C3a and terminal complement complex. Soluble complement receptor 1 resulted in a significant reduction in C3a levels (p < 0.01) but did not inhibit terminal complement complex generation. A marked rise in neutrophil CD11b/CD18 expression, simultaneous loss of L-selectin expression, and a progressive accumulation of plasma elastase-alpha 1-antitrypsin occurred and were not affected by soluble complement receptor. However, generation of interleukin-8 in the circuits was inhibited (p < 0.05) by pretreatment with soluble complement receptor. These data suggest that changes in neutrophil activation seen during cardiopulmonary bypass may not be induced directly by anaphylatoxin generation.

Release of interleukin-8 and calprotectin during and after paediatric cardiopulmonary bypass with and without ultrafiltration

Release of calprotectin and interleukin-8 (IL-8), changes in leukocyte counts and subsets and influence of extracorporeal ultrafiltration were evaluated during and after cardiopulmonary bypass (CPB) in 18 children undergoing open-heart surgery for congenital heart anomalies. Ultrafiltration was used in nine cases and nine were controls. Calprotectin concentration rose after start of CPB, peaking 48 hours postoperatively, with no significant intergroup difference. Positive correlation was found between duration of CPB and calprotectin (peak level and accumulated total). Circulating IL-8 was detected in all patients perioperatively, peaking at wound closure in the ultrafiltration group and at termination of bypass in the controls. CPB duration correlated significantly to peak level and accumulated total of IL-8. Seven of nine ultrafiltrate samples contained IL-8 at levels similar to the plasma concentration. Changes in white cell counts were mainly attributable to neutrophils. The two subgroups did not differ significantly in neutrophil counts. Neutropenia found after 10 minutes of CPB was replaced by neutrophilia, with maximal values postoperatively. Calprotectin and IL-8 thus were released into the circulation during CPB in children. Ultrafiltration did not affect the plasma concentrations of these substances, and only IL-8 was detected in the ultrafiltrate.

Anti-CD11b monoclonal antibody improves myocardial function after six hours of hypothermic storage

BACKGROUND

The shortage of pediatric heart donors often necessitates considerable travel time and, as a result, prolonged donor heart ischemia. This excessive hypothermic storage may contribute markedly to myocardial dysfunction in the recipient.

METHODS

We investigated the role of leukocyte-endothelial interactions in this dysfunction in an isolated, immature (mean age, 11.8 +/- 1.6 days) swine heart model using a monoclonal antibody against a leukocyte adhesion molecule. We studied a total of 20 hearts subjected to 6 hours of cardioplegic arrest at 4 degrees C. Group M1/70 (n = 6) received at reperfusion 15 micrograms/mL of a monoclonal antibody F(ab')2 fragment to CD11b, the alpha-subunit of the leukocyte adhesion molecule Mac-1. Group MB10.6 (n = 8) received 15 micrograms/mL of the swine unreactive F(ab')2 MB10.6, and the third group received saline vehicle.

RESULTS

Administration of M1/70 resulted in improved postischemic recovery of ventricular function compared with the two control groups (p < 0.05).

CONCLUSIONS

These data implicate leukocyte-endothelial interactions mediated by the leukocyte adhesion molecule CD11b in myocardial dysfunction after long-term hypothermic ischemia. Specific antiadhesion strategies such as this may safely extend storage time for pediatric donor hearts.

Heparin-coated cardiopulmonary bypass circuits: hemostatic alterations and postoperative blood loss

This prospective, randomized study involving patients undergoing isolated coronary artery bypass grafting investigated whether the use of heparin-coated bypass circuits with an uncoated cardiotomy reservoir (n = 10) compared with standard uncoated bypass circuits (n = 10) resulted in differences in patient outcome and hemostatic alterations. There were no differences in postoperative blood loss, transfusion requirements, and routine coagulation test results between groups. Immunoassays for platelet alpha-granule constituents platelet factor 4 and beta-thromboglobulin, thrombin generation by-product F1.2, fibrinopeptide A, thrombin-antithrombin complex, and fibrinolysis by-product D-dimer also demonstrated no significant differences between groups, although trends for lower platelet secretion with heparin coating were noted. Increases were found in beta-thromboglobulin and platelet factor 4 concentrations at 10 (p < 0.03) and 30 minutes (p < 0.001) of CPB, respectively, and continuing throughout CPB (p < 0.001) for both groups versus values measured before incision. No significant differences were seen between levels 5 minutes prior to aortic cross-clamp release and those obtained 8 and 45 minutes after cross-clamp release. Conversely, no significant increases in F1.2, thrombin-antithrombin complex, and D-dimer were seen prior to release of the aortic cross-clamp, but afterward increases occurred that were highly significant (p < 0.001). The temporal data suggest that platelet activation occurs primarily as a result of contact with the cardiopulmonary bypass circuitry, whereas thrombin generation and fibrinolytic activity are not significant until reperfusion of the heart and lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Complement and neutrophil activation during cardiopulmonary bypass: a study in the complement-deficient dog

Cardiopulmonary bypass (CPB) is known to cause complement and neutrophil activation, but the relative importance and interaction of these components in CPB-induced inflammation is unknown. In this study, a strain of dogs genetically deficient in the third component of complement (C3) was used to determine the contribution of C3 to neutrophil activation and pulmonary injury after CPB. Eleven dogs (5 C3-deficient and 6 controls) underwent 150 minutes of hypothermic CPB (28 degrees C) followed by 2 hours of observation. Before CPB, C3 levels were normal in controls and less than 1% of normal in C3-deficient dogs. In control dogs, functional activity of C3 decreased to 53.2% of baseline after 1 hour of CPB and there was immunohistochemical evidence of C3 deposition in lung after CPB; C3-deficient dogs had no C3 deposition in lung. Although similar degrees of neutropenia occurred during CPB in the two groups, expression of neutrophil adhesion molecule subunit CD18 was significantly lower in C3-deficient dogs than controls after 1 hour of CPB (45.9 +/- 3.7 versus 82.9 +/- 10.0 mean fluorescence units; p < 0.02). Postbypass lung tissue myeloperoxidase content was also less in C3-deficient dogs (43.8 +/- 4.6 versus 71.1 +/- 8.6 mumol x 10 mg-1 x min-1; p < 0.03). Cardiopulmonary bypass-associated lung injury (assessed by alveolar-arterial oxygen gradient, pulmonary vascular resistance, percent lung water, and light and electron microscopic appearance) was similar between groups. These results demonstrate that (1) C3 is deposited on pulmonary vascular endothelium during CPB and (2) C3 mediates increased expression of neutrophil CD18 and neutrophil sequestration in lung after CPB.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of definitions and parameters for sepsis assessment in patients after cardiac surgery

In 110 patients undergoing elective heart surgery on extracorporeal circulation, various parameters were studied regarding the early assessment of septic complications. In a first step, the Elebute score definition for postoperative sepsis validated in general surgery patients (score > or = 12) could be confirmed in an extended form (> or = 12 on > or = 2 days) for cardiac surgery patients. According to this definition (overall classification accuracy for clinically defined sepsis-related mortality: 94%), septic complications occurred in 16 patients and were associated with a significantly worse prognosis than in non-septic patients (mortality 69% vs. 1%, p < 0.0001). In contrast, SIRS (best classification criterion: positive on > or = 3 days) displayed a lower specificity for clinically defined sepsis-related mortality, at least during the early postoperative course (accuracy: 67%). Based on the Elebute score classification, other more practicable parameters were investigated regarding their usefulness for an early sepsis risk assessment in post cardiac surgical patients. Five additional severity scores (APACHE II, MOF-Goris, HIS, SAPS, SSS) were comparable (ROC area: 0.94 to 0.96) and superior to plasma PMN-elastase and neopterin, haemodynamics and clinical parameters in predicting the risk for septic complications as early as by the first postoperative day.

Early and late effects of leukopenic reperfusion on the recovery of cardiac contractile function. Studies in the transplanted and isolated blood-perfused rat heart

BACKGROUND

Since there is considerable evidence that leukocytes contribute to tissue injury during ischemia and reperfusion, the present study was designed to: (1) determine whether reperfusion in vivo with leukopenic blood affords protection in a model of reversible hypothermic ischemia, (2) determine the duration of any protection, (3) characterize the relation between protection and duration of leukopenic perfusion, and (4) assess the effect of leukopenic reperfusion on myocardial glutathione content.

METHODS AND RESULTS

Rat hearts (n = 12 per group) were excised, immediately arrested with an infusion (2 minutes at 4 degrees C) of St Thomas' cardioplegic solution, and subjected to 4 hours of global ischemia (4 degrees C). The hearts were then transplanted (1 hour additional ischemic time) into the abdomen of saline-treated or leukopenic recipients. Leukopenia was induced by intraperitoneal administration of mustine hydrochloride (2 mg/kg) 3 days before study. Hearts were then reperfused in situ for 1, 4, or 24 hours, after which they were excised and either processed for histological examination (n = 4 per group) or perfused aerobically with bicarbonate buffer for 20 minutes, and contractile function was assessed (n = 8 per group); at the end of this period, some hearts (n = 5 per group) were taken for metabolite analysis. After 1 hour of reperfusion, contractile function in the saline-treated control group was significantly reduced compared with aerobic controls that had not been subjected to ischemia (left ventricular developed pressure [LVDP], 108 +/- 5 vs 126 +/- 3 mm Hg at an end-diastolic pressure of 12 mm Hg; P < .05). However, in the hearts with leukopenic reperfusion, LVDP (119 +/- 2 mm Hg) was similar to that of aerobic controls. This benefit, however, was lost after 4 and 24 hours of reperfusion. Cardiac compliance was not influenced by leukopenia. Coronary flow recovered significantly better in the leukopenic hearts during the first 4 hours of reperfusion (11.8 +/- 0.5 vs 9.3 +/- 0.4 mL/min at 1 hour and 10.0 +/- 0.5 vs 8.0 +/- 0.4 mL/min at 4 hours, P < .05), but again this benefit was lost after 24 hours of reperfusion. The myocardial contents of reduced and oxidized glutathione after 1, 4, and 24 hours of reperfusion were similar in saline-treated and leukocyte-depleted animals. In additional studies, the period of ischemia was extended to 8 hours, and similar results were obtained, with improved recovery of contractile function and coronary flow but not cardiac compliance in the leukopenic group after 1 hour of reperfusion. In further studies with the isolated blood-perfused rat heart, ischemia was induced for 8 hours; this was followed first by reperfusion for 0, 2, 10, 30, or 60 minutes with leukopenic blood and then by perfusion with blood from saline-treated animals for 60, 58, 50, 30, or 0 minutes, respectively. Reperfusion with leukopenic blood for 2 minutes did not improve the recovery of LVDP (106 +/- 7 vs 96 +/- 10 mm Hg in controls; NS) but when continued for 10, 30, or 60 minutes resulted in significant improvements (137 +/- 5, 138 +/- 3, and 150 +/- 10 mm Hg, respectively). Although coronary flow tended to be greater in all leukopenic groups, by the end of 60 minutes of reperfusion, only those hearts reperfused with leukopenic blood for the entire reperfusion period showed a significant improvement (3.4 +/- 0.3 vs 2.5 +/- 0.2 mL/min in controls; P < .05). Histological studies revealed no intravascular aggregation of leukocytes or features of myocyte necrosis.

CONCLUSIONS

Reperfusion with leukopenic blood accelerated the rate of recovery of cardiac function after reversible myocardial injury but did not lead to a sustained increase in the eventual extent of recovery. Reperfusion with leukopenic blood for the first 10 minutes of reflow is sufficient to obtain this benefit.

Tissue factor is expressed on monocytes during simulated extracorporeal circulation

Certain forms of extracorporeal circulation exemplified by cardiopulmonary bypass require continuous high-dose anticoagulation to prevent thromboembolic complications. We hypothesized that monocytes may be stimulated to express tissue factor (TF) during prolonged simulated extracorporeal circulation. TF was identified both by flow cytometry by using three TF-specific monoclonal antibodies and functional assay of procoagulant activity (PCA). TF significantly increased between 2 and 6 hours of simulated extracorporeal circulation by both analyses. Relative fluorescence on monocytes increased from a control value of 100 to 313 +/- 79 on cells from the simulated extracorporeal circuit (p < 0.05). PCA increased from 21 +/- 8 to 775 +/- 326 pg TF/10(6) monocytes (p < 0.05) and was blocked 99.6% by preincubation of cells with a mixture of monoclonal antibodies to TF. By 6 hours, the number of leukocytes in the circuit was decreased by 43%. The cells were recovered from the oxygenator membrane by washing with EDTA. Compared with initial values, by 6 hours, both TF antigen at 378 +/- 90 (p < 0.05) and PCA at 1,357 +/- 280 pg TF/10(6) monocytes (p < 0.01) were highest in the recovered cells. Cells incubated for 6 hours and not subjected to simulated extracorporeal circulation did not increase TF. Examination of monocytes for the adhesive receptor CD11b/18 (Mac-1) paralleled TF expression, providing an additional putative receptor for the coagulant proteins, factor X and fibrinogen or fibrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Inflammatory response to cardiopulmonary bypass

Cardiac operations with cardiopulmonary bypass cause a systemic inflammatory response, which can lead to organ injury and postoperative morbidity. Causative factors include surgical trauma, contact of blood with the extracorporeal circuit, and lung reperfusion injury on discontinuing bypass. Advances in immunological techniques have allowed measurement of both plasma and intracellular components of this multifaceted perioperative response. This includes activation of the complement, coagulation, fibrinolytic, and kallikrein cascades, activation of neutrophils with degranulation and protease enzyme release, oxygen radical production, and the synthesis of various cytokines from mononuclear cells (including tumor necrosis factor, interleukin-1, and interleukin-6). Advances in our understanding of the interactions between these markers of cellular and humoral responses to cardiopulmonary bypass will enable more effective intervention to reduce the deleterious effects and improve the outlook for patients undergoing cardiac operations beyond the 1990s.

The calcium channel blocker nifedipine fails to inhibit leucocyte elastase release during cardiopulmonary bypass

Circulating concentrations of leucocyte elastase were measured in 16 adult patients undergoing cardiopulmonary bypass (CPB) with a flat-sheet membrane oxygenator. Eight patients (Group I) received the calcium channel blocker nifedipine (9 micrograms.kg-1 x h-1) during CPB. Eight patients (Group II) did not receive any calcium channel blocker during surgery and served as the control group. Elastase concentrations were measured at 7 time points: 2 before, 2 during, and 3 after CPB. The bypass procedure was associated with elevation in elastase concentrations (P < 0.001). Comparing to baseline values elastase concentrations were significantly elevated (P < 0.05) 60 min after the start of CPB and on all measurements done after CPB. Elastase concentrations correlated with the duration of CPB (rs = 0.76, P < 0.001), and were not influenced by nifedipine infusion as revealed by comparing the two groups. This study demonstrates moderate elastase release during CPB with a flat-sheet membrane oxygenator and fails to confirm inhibition of elastase release by nifedipine infusion during CPB.

Time for new concepts about measurement of complement activation by cardiopulmonary bypass?

Fifty-one patients admitted for routine coronary bypass operations were randomized to cardiopulmonary bypass with a membrane oxygenator (Capiox) or a bubbler (Polystan or William Harvey). Complement activation was measured using enzyme immunoassays for concentrations of C3 activation products and the terminal complement complex. From 5.8 to 8.1 arbitrary units (AU)/mL (medians), the plasma concentrations of C3 activation products increased by 119.9 AU/mL (Capiox), 124.6 AU/mL (Polystan), and 79.5 AU/mL (William Harvey) to a peak at closure of the sternum (not significant when related to baseline concentrations). The increase in C3 activation products and baseline C3 activation were linearly correlated (R2 = 0.30; p less than 0.0001). From 5.5 to 6.1 AU/mL, the plasma terminal complement complex concentrations increased by 45.2 AU/mL (Capiox), 15.4 AU/mL (Polystan), and 17.4 AU/mL (William Harvey) to a peak before termination of cardiopulmonary bypass. Maximal terminal (C5-C9) activation was significantly higher in the membrane oxygenator group (p less than 0.0001) and showed no relationship to C3 activation. Measurement of C3 activation only gives no information about C5-C9 activation. At present, terminal complement complex quantitation is probably the best index of C5-C9 activation during cardiopulmonary bypass.