Efficiency and safety of leukocyte filtration during cardiopulmonary bypass for cardiac surgery

Leukocyte filtration and leukocyte modulation therapy during extracorporeal cardiopulmonary resuscitation in a porcine model of prolonged cardiac arrest

Extracorporeal cardiopulmonary resuscitation (ECPR) is emerging as a feasible and effective rescue strategy for prolonged cardiac arrest (CA). However, prolonged total body ischemia and reperfusion can cause microvascular occlusion that prevents organ reperfusion and recovery of function. One hypothesized mechanism of microvascular "no-reflow" is leukocyte adhesion and formation of neutrophil extracellular traps. In this study we tested the hypothesis that a leukocyte filter (LF) or leukocyte modulation device (L-MOD) could reduce NETosis and improve recovery of heart and brain function in a swine model of prolonged cardiac arrest treated with ECPR. Thirty-six swine (45.5 ± 2.5 kg, evenly distributed sex) underwent 8 min of untreated ventricular fibrillation CA followed by 30 min of mechanical CPR with subsequent 8 h of ECPR. Two females were later excluded from analysis due to CPR complications. Swine were randomized to standard care (Control group), LF, or L-MOD at the onset of CPR. NET formation was quantified by serum dsDNA and citrullinated histone as well as immunofluorescence staining of the heart and brain for citrullinated histone in the microvasculature. Primary outcomes included recovery of cardiac function based on cardiac resuscitability score (CRS) and recovery of neurologic function based on the somatosensory evoked potential (SSEP) N20 cortical response. In this model of prolonged CA treated with ECPR we observed significant increases in serum biomarkers of NETosis and immunohistochemical evidence of microvascular NET formation in the heart and brain that were not reduced by LF or L-MOD therapy. Correspondingly, there were no significant differences in CRS and SSEP recovery between Control, LF, and L-MOD groups 8 h after ECPR onset (CRS = 3.1 ± 2.7, 3.7 ± 2.6, and 2.6 ± 2.6 respectively; p = 0.606; and SSEP = 27.9 ± 13.0%, 36.7 ± 10.5%, and 31.2 ± 9.8% respectively, p = 0.194). In this model of prolonged CA treated with ECPR, the use of LF or L-MOD therapy during ECPR did not reduce microvascular NETosis or improve recovery of myocardial or brain function. The causal relationship between microvascular NETosis, no-reflow, and recovery of organ function after prolonged cardiac arrest treated with ECPR requires further investigation.

The scientific evidence of arterial line filtration in cardiopulmonary bypass

BACKGROUND

The indication for arterial line filtration (ALF) is to inhibit embolisation during cardiopulmonary bypass. Filtration methods have developed from depth filters to screen filters and from a stand-alone component to an integral part of the oxygenator. For many years, ALF has been a standard adopted by a majority of cardiac centres worldwide. The following review aims to summarize the available evidence in support for ALF and report on its current practice in Europe.

METHOD

The principles and application of ALF in Europe was investigated using a survey conducted in 2014. The scientific evidence for ALF was examined by performing a systematic literature search in six different databases, using the following search terms: "Cardiopulmonary bypass AND filters AND arterial". The primary endpoint was protection against cerebral injury verified by the degree of cerebral embolisation or cognitive tests. The secondary endpoint was improvement of the clinical outcome verified elsewise. Only randomised clinical trials were considered.

RESULTS

The response rate was 31% (n=112). The great majority (88.5%) of respondents were using ALF, following more than 10 years of experience. Integrated arterial filtration was used by 55%. Of respondents not using ALF, fifty-four percent considered starting using integrated arterial filtration. The systematic literature database search returned 180 unique publications where 82 were specifically addressing ALF in cardiopulmonary bypass. Only four out of the 82 identified publications fulfilled our inclusion criteria. Of these, three were more than 20 years old and based on the use of bubble oxygenation.

CONCLUSION

ALF is a standard implemented in a majority of cardiopulmonary bypass procedures in Europe. The level of scientific evidence available in support of current arterial line filtration methods in cardiopulmonary bypass is, however, poor. Large, well-designed, randomised trials are warranted.

Leukodepletion for patients undergoing heart valve surgery

BACKGROUND

There is some evidence for the benefits of leukodepletion in patients undergoing coronary artery surgery. Its effectiveness in higher risk patients, such as those undergoing heart valve surgery, particularly in terms of overall clinical outcomes, is currently unclear.

OBJECTIVES

To assess the beneficial and harmful effects of leukodepletion on clinical, patient-reported and economic outcomes in patients undergoing heart valve surgery.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 3 of 12) in The Cochrane Library, the NHS Economic Evaluations Database (1960 to April 2013), MEDLINE Ovid (1946 to April week 2 2013), EMBASE Ovid (1947 to Week 15 2013), CINAHL (1982 to April 2013) and Web of Science (1970 to 17 April 2013) on 19 April 2013. We also searched the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP), the US National Institutes of Health (NIH) clinical trials database and the International Standard Randomised Controlled Trial Number Register (ISRCTN) in April 2013 for ongoing studies. No language or time period restrictions were applied. We examined the reference lists of all included randomised controlled trials and contacted authors of identified trials. We searched the 'grey' literature at OpenGrey and handsearched relevant conference proceedings.

SELECTION CRITERIA

Randomised controlled trials comparing a leukocyte-depleting arterial line filter with a standard arterial line filter, on the arterial outflow of the heart-lung bypass circuit, in elective patients undergoing heart valve surgery.

DATA COLLECTION AND ANALYSIS

Data were collected on the study characteristics, three primary outcomes (1. post-operative in-hospital all-cause mortality within three months, 2. post-operative all-cause mortality excluding inpatient mortality < 30 days, 3. length of stay in hospital, 4. adverse events and serious adverse events) and seven secondary outcomes (1. tubular or glomerular kidney injury, 2. validated health-related quality of life scales, 3. validated renal injury scales, 4. use of continuous veno-venous haemo-filtration, 5. length of stay in intensive care, 6. costs of care). Data were extracted by one author and verified by a second author. Insufficient data were available to perform a meta-analysis or sensitivity analysis.

MAIN RESULTS

Eight studies were eligible for inclusion in the review but data on prespecified review outcomes were available from only one, modestly powered (24 participants) study (Hurst 1997). There were no differences between a leuko-depleting versus standard filter in length of stay in the intensive care unit (ICU) (mean difference (MD) 0.80 days; 95% confidence interval (CI) -0.24 to 1.84) or length of hospital stay (MD 0.20 days; 95% CI -1.78 to 2.18).

AUTHORS' CONCLUSIONS

There are currently insufficient good quality trials with valve surgery patients to inform recommendations for changes in clinical practice. A future National Institute for Health Research (NIHR)-funded feasibility study (recruiting mid-year 2013) comparing leukodepletion with a standard arterial line filter in patients undergoing elective heart valve surgery (the ROLO trial) will be the largest study to date and will make a significant contribution to future updates of this review.

A selective cytopheretic inhibitory device for use during cardiopulmonary bypass surgery

BACKGROUND

Systemic inflammatory response syndrome (SIRS) can occur in association with cardiopulmonary bypass (CPB) surgery, resulting in multiple organ dysfunction (MOD). Activated neutrophils have been implicated as major inciting factors in this process. Neutrophil-depleting filters incorporated within the extracorporeal blood circuit during CPB have been developed and evaluated, with inconsistent clinical results.

METHODS

A novel, biomimetic, selective cytopheretic device (SCD) was tested in vitro within a blood circuit to assess safety and interactions with blood components and further evaluated ex vivo in a bovine model of CPB surgery during ventricular assist device implantation.

RESULTS

In vitro blood circuit studies demonstrated that the SCD reduces circulating neutrophils while maintaining low rates of hemolysis compared to current leukocyte-reduction filters. In the bovine CPB model, animals without SCD treatment (No SCD) demonstrated an increase in circulating white blood cell (WBC) and neutrophil counts, steadily increasing throughout CPB. SCD with only systemic heparin anticoagulation (SCD-H) acutely reduced neutrophils for the first 2 hrs of CPB, but followed with a greater than 6-fold increase in neutrophil counts. SCD treatment with regional citrate anticoagulation along the SCD circuit (SCD-C) reduced systemic neutrophil counts throughout 4 hrs of CPB despite lower amounts of eluted cells from the SCD. When analyzed for immature neutrophils, the control and SCD-H showed increasing counts at later time-points, not seen in the SCD-C group, suggesting a more complex mechanism of action than simple leukoreduction.

CONCLUSIONS

These results suggest that SCD-C therapy may disrupt the systemic leukocyte response during CPB, leading to improved outcomes for CPB-mediated MOD.

Does Systemic Leukocyte Filtration Affect Perioperative Hemorrhage in Cardiac Surgery? A Systematic Review and Meta-Analysis

Cardiopulmonary bypass causes a systemic inflammatory reaction. Activation of leukocytes is an important part of this process, and is known to directly contribute to the development of postoperative coagulopathy, and thus hemorrhage. The removal of leukocytes from the cardiopulmonary bypass circulation, using specialized filters, has been proposed as one method for attenuating this inflammatory response. However, there is no consensus on its effectiveness. We used meta-analytical techniques to systematically assess the literature reporting on the potential effect of systemic leukofiltration on perioperative hemorrhage. Random effects modeling was used to calculate overall estimate, and heterogeneity was assessed. Systemic leukofiltration made no significant impact on chest tube drainage in the first 24 hours (weighted mean difference [WMD], x23.9 ml; 95% confidence interval [CI], x95.48-47.61; p = 0.51) or on the total packed red cell transfusion requirements of each patient (WMD, 7.84 ml; 95% CI, x80.13-95.81; p = 0.86). The studies performed in this area thus far are highly heterogeneous, due in part to relatively poor-quality design and inadequate matching of their study groups. Although further high-quality trials on systemic leukofiltration may be appropriate, other strategies to reduce the coagulopathy associated with cardiopulmonary bypass should be sought and evaluated.

The effects of various leukocyte filtration strategies in cardiac surgery

It is known that cardiopulmonary bypass causes an inflammatory reaction with an associated morbidity and mortality. Several anti-inflammatory strategies have been implemented to reduce this response, including leukocyte removal from the circulation using specialised filters. The aim of this study is to systematically review the available evidence on leukocyte filtration in cardiac surgery, focusing on its effect on systemic inflammation and whether this has influenced clinical outcomes. Five electronic databases were systematically searched for studies reporting the effect of leukocyte filtration at any point within the cardiopulmonary bypass circuit in humans. Reference lists of all identified studies were checked for any missing publications. Two authors independently extracted the data from the included studies. Whilst systemic leukodepleting filters do not appear to consistently lower leukocyte counts, they may preferentially remove activated leukocytes. Small improvements in early post-operative lung function in patients receiving systemic leukodepletion have been reported, but this does not lead to reduced hospital stay or decreased mortality. There is substantial evidence that cardioplegic leukocyte filtration attenuates the reperfusion injury at a cellular level, but this has not been translated into clinical improvements. Finally, whilst various strategies involving multiple leukocyte filters, or the incorporation of pharmacological agents into leukocyte-depleting protocols have been evaluated, the current available results are not conclusive. Our study suggests that there is not enough high quality or consistent evidence to draw guidelines regarding the use of leukocyte-depleting filters within routine cardiac surgical practice.

Clinical benefits of continuous leukocyte filtration during cardiopulmonary bypass in patients undergoing valvular repair or replacement

Valve operations in the form of repair or replacement make up a significant population of patients undergoing surgical procedures in the USA annually with the use of cardiopulmonary bypass. These patients experience a wide range of complications that are considered to be mediated by activation of complement and leukocytes. The extracorporeal perfusion circuit consists of multiple synthetic artificial surfaces. The biocompatibility of the blood contact surfaces is a variable that predisposes patients to an increased risk of complement mediation and activation. This can result in an inflammatory process, causing leukocytes to proliferate and sequester in the major organ systems. The purpose of this study was to determine whether filtration of activated leukocytes improved clinical outcomes following surgical intervention for valve repair or replacement. In this paper, we report a retrospective matched cohort study of 700 patients who underwent valve procedures from June 1999 to December 2002. The control group (CG) consisted of patients who had a conventional arterial line filter. In the study group (SG), patients had a conventional arterial line filter and a leukocyte arterial line filter (Pall Medical, NY). In the SG, blood diverted to the cardioplegia system was also leukocyte depleted to enhance myocardial preservation by adapting this device to the outflow port on the filter. Patient characteristics were similar for the SG and the CG, including 228 males and 122 females, mean age (62.4 versus 64.2 years), cardiopulmonary bypass time (127+/-64 versus 116+/-53 min), and aortic crossclamp time (84+/-23 versus 81+/-23 min). Our results demonstrate that the SG achieved statistically significant reduction in the time to extubation (p =0.03) and the number of patients with prolonged intubation in excess of 24 hours (p <0.04), in addition to improved postoperative oxygenation (p=0.01), and decreased length of hospital stay (p =0.03). We believe that leukocyte filters are clinically beneficial, as demonstrated by the results presented in this study.

First Efficacy and Safety Results with the Antibody Containing Leukocyte Inhibition Module in Cardiac Surgery Patients with Neutrophil Hyperactivity

Systemic administration of immune modulating antibodies may play an important role in reducing neutrophil hyperactivity, for example, in patients undergoing cardiac surgery with extracorporeal circulation or in trauma patients. However, this strategy has extremely high costs and is often associated with severe adverse effects. We developed the Leukocyte-Inhibition-Module (LIM), an extracorporeal circulation (ECC) device housing a polyurethane matrix with covalently bound Fas (CD95; APO-1) stimulating antibodies to rapidly prevent neutrophil hyperactivation. A feasibility study with 14 patients undergoing cardiac surgery with the use of immunogenic ECC without (n = 5) and with (n = 9) LIM (venous line) was performed. Our data show that the usually observed ECC associated perioperative increase in neutrophils (control) was prevented by LIM (p = 0.023). Moreover, the increase of the proinflammatory markers tumor necrosis factor (TNF)-alpha and polymorphonuclear elastase was limited by LIM (p = 0.038 and p = 0.002). In both groups, no significant changes in liver enzymes or in clotting were detected after surgery, and up to 12 months follow up, no unusual complications were reported. This study shows for the first time to our knowledge the feasibility, efficacy, and safety of a new cost effective, immune management strategy in patients with aberrant immune activation by exposing the blood stream to immobilized agonistic anti-Fas antibodies.

Clinical Effectiveness of Leukocyte Filtration During Cardiopulmonary Bypass in Patients with Chronic Obstructive Pulmonary Disease

BACKGROUND

We tested the hypothesis that leukocyte filtration during pulmonary reperfusion preserves pulmonary function and results in improved oxygenation after cardiopulmonary bypass (CPB) in patients with chronic obstructive pulmonary disease (COPD).

METHODS

In a prospective, randomized study, the treatment group consisted of 20 patients with COPD from consecutive open-heart procedures. A primed leukocyte filter was connected to the arterial line downstream of the standard arterial filter but was excluded from circulation. Circulated blood was directed through the leukocyte filter approximately 10 minutes before aortic cross-clamp removal and at early reperfusion for up to 30 minutes. These patients were compared to 20 additional COPD patients (controls) on whom systemic leukocyte filtration was not used during open-heart surgery.

RESULTS

There was no significant difference in gender, age, left ventricular ejection fraction, type of procedure, aortic cross-clamp time, perfusion time, preoperative FEV1 and preoperative respiratory index (Pao2/FiO2 ratio) between treatment and control groups. The respiratory index changed in the treatment group by +9.8% of baseline after completion of CPB, by -14.2% upon arrival in the intensive care unit (ICU), and by -19.6% 12 hours later, whereas in the control group, it changed by -14.5% (p < 0.05), -27.7%, and -24%, respectively. Leukocyte-depleted patients required shorter intubation time (20.4 +/- 16.1 hours), ICU stay (46.2 +/- 40.1 hours) and length of hospitalization (8.3 +/- 2.8 days) than controls (29.5 +/- 21.9 hours, p < 0.05; 75.5 +/- 34.9 hours, p < 0.005; and 10.4 +/- 3.5 days, p < 0.05, respectively). Surgical (30-day) mortality was zero in both groups.

CONCLUSIONS

In COPD patients having CPB, systemic leukocyte depletion at early reperfusion was associated with better oxygenation, shorter intubation time, and shorter ICU and hospital stays. Leukocyte filtration during CPB most likely preserves pulmonary function by ameliorating pulmonary reperfusion injury.

Universal leukodepletion of blood components results in a significant reduction of febrile non-hemolytic but not allergic transfusion reactions

BACKGROUND

Universal leukodepletion of blood components to prevent acute non-hemolytic transfusion reactions (NHTRs) is still a subject of debate.

PATIENTS AND METHODS

Transfusion-associated NHTRs observed at our hospital in the last 6 years were retrospectively analyzed. Buffy-coat depleted red blood cells (bc-RBCs), and if indicated, leucodepleted post-storage (ld-RBCs) were initially used. In April 1997, universal leukodepletion was implemented at our hospital, and thereafter only prestorage ld-RBCs were used. All platelet concentrates transfused during this time were prestorage filtered single-donor apheresis platelets (SDAPs).

RESULTS

A total of 163,090 blood products were transfused from April 1995 to April 2001 (bc-RBC: n=34,040 units; ld-RBC: n=66,967; SDAP: n=14,516; FFP: n=47,567). The number of post-transfusion febrile NHTRs occurring with each blood product was 65 (0.19%) for bc-RBCs, 8 (0.16%) for post-storage ld-RBCs, 16 (0.03%) for prestorage ld-RBCs, 16 (0.11%) for SDAPs, and 10 (0.02%) for FFP. Allergic reactions (n=116) were most frequently observed after SDAP transfusion (0.32%) and occurred at a similarly low rate after transfusion of all other blood components (0.03-0.08%).

CONCLUSION

In conclusion, acute NHTRs rarely occur after the use of leukodepleted blood components. Prestorage appears to be more effective than post-storage leukodepletion in preventing febrile reactions following a blood transfusion.

A review of leukofiltration in cardiac surgery: the time course of reperfusion injury may facilitate study design of anti-inflammatory effects

The systemic inflammatory response syndrome (SIRS) is a well-recognized phenomenon attending cardiopulmonary bypass (CPB) surgery. SIRS leads to costly complications and several strategies intended to ameliorate the symptoms have been studied, including leukocyte reduction using filtration. Although the body of work suggests that leukoreduction attenuates SIRS, discrepancies remain within the literature. The recent literature is reviewed, highlighting the areas where concordance is lacking. Investigations into many promising device-related technologies are often deterred by the high costs of clinical trials. Adding to costs is the fact that clinical end points generally require large sample sizes. An understanding, however, of the pathogenesis of reperfusion injury can guide the investigator to choose physiologic response measures that correlate well with clinical outcome, but feature low inherent variability, allowing for clinical trials with smaller sample sizes. With this goal in mind, a model for the pathogenesis of reperfusion injury is described. Using a model of reperfusion injury as underpinnings for the design of prospective pilot studies, we show that salvaged blood reinfused following CPB elicits time-dependent effects on pulmonary function as predicted by the model. Data are illustrative of principles that could expand the scope of clinical investigations designed to validate the use of physiologic response measures as correlates of clinical outcome. Such investigations would target surrogate markers of clinical outcome, measured at clinically relevant times. Once validated, these surrogate markers would, thereafter, become economical screening tools for clinical studies of device-related or pharmacological anti- inflammatory interventions.

Leukocyte filtration in cardiac surgery: a review

Leukocyte filtration has evolved as an important technique in cardiac surgery with cardiopulmonary bypass to prevent pathogenic effector functions mediated by activated leukocytes. The underlying mechanisms that result in an improvement of laboratory variables as well as clinical outcome are not resolved yet. Moreover, the optimum strategy for the use of current filtration technology has not been systematically evaluated. This paper, therefore, reviews how activated leukocytes may lead to tissue damage, summarizes the known effects of leukocyte filtration on clinical outcome and laboratory parameters, and deals with current experimental and clinical efforts to further limit the pathogenic effects of leukocytes in cardiac surgery.

Bradykinin production during donor plasmapheresis procedures

BACKGROUND AND OBJECTIVES

Extracorporeal circuits made of artificial substances may induce blood cells and humoral activation. Negatively charged surfaces may activate Factor XII and the prekallikrein-kinin cascade, resulting in bradykinin (BK) production. BK has been considered to be involved in severe hypotensive reactions occurring during therapeutic apheresis in patients taking angiotensin-converting enzyme (ACE) inhibitors or in those receiving platelet transfusion. In this study we investigated BK production during donor plasmapheresis procedures.

PATIENTS AND METHODS

Eighteen volunteer donors entered the study protocol. Nine of them were taking ACE inhibitors. Their blood pressure (BP) was monitored both pre- and post-apheresis, and BK determination was carried out using a competitive enzyme immunoassay (EIA), in plasma samples collected both during and at completion of the procedure. In addition, a limited number of thawed plasma units were checked for BK.

RESULTS

No side-effects were observed during the procedures. However, donors taking ACE inhibitors showed a higher variation of their systolic BP compared to those who were not taking ACE inhibitors, while diastolic BP percentage variations did not differ significantly between the two groups. The BK concentration was considerably higher in donors taking ACE inhibitors: 183 +/- 26 versus 82 +/- 6 ng/ml (P < 0.0001) after the first collection cycle and 142 +/- 20 versus 65 +/- 11 ng/ml (P < 0.0001) in the final samples. BK was also detected, at a lower concentration (15 ng/ml), in one out of four thawed plasma units obtained from donors taking ACE inhibitors and at 1 ng/ml in one out of two thawed plasma units from the control group.

CONCLUSION

Donors taking ACE inhibitors and undergoing plasmapheresis showed higher levels of BK compared to the control group. Furthermore, the detection of BK in plasma units after a freeze-thaw procedure might explain the sudden hypotensive reaction occurring during therapeutic plasma exchange when plasmapheresis units are adopted as substitution fluids. Further investigations are needed to assess the real clinical importance of the presence of BK in plasma units.

Timing of leukocyte filtration during cardiopulmonary bypass

The effects of leukocyte filtration on the outcome of cardiac surgery with cardiopulmonary bypass (CPB) have been shown by numerous investigators. In the majority of cases a leukocyte filter is placed in the arterial line instead of a standard arterial line filter and used throughout CPB. However, protocols to optimize onset and duration of leukocyte filtration have not been sufficiently evaluated to date. In this paper, current efforts to improve such protocols are demonstrated and discussed. These efforts are based on studies of leukocyte pathogenicity during cardiac surgery. A first study (double-blind randomized) was performed in routine coronary artery bypass graft (CABG) patients to evaluate whether short-term leukocyte filtration during reperfusion by release of the aortic crossclamp would reduce reperfusion-associated myocardial damage. Further data compare the efficacy of three different filtration concepts to reduce CPB- and/or reperfusion-associated leukocyte pathogenicity. Clinical endpoints, standard laboratory variables and functional in vitro assays are provided and discussed.