Phosphorylcholine coating of extracorporeal circuits provides natural protection against blood activation by the material surface

Health Technology Assessment of Cardiopulmonary Bypass Circuit with and without Phosphorylcholine Coating: A Retrospective Study on Safety and Efficiency in Cardiac Surgery

BACKGROUND

Phosphorylcholine has emerged as a potential adjunctive agent in cardiopulmonary bypass (CPB) circuits. Phosphorylcholine serves as a coating for the CPB circuit, potentially enhancing biocompatibility and reducing thrombotic events. However, its impact on specific patient populations and procedural outcomes remains underexplored.

MATERIALS AND METHODS

In this retrospective study, we analyzed data from 60 patients who underwent cardiac surgery with CPB, comprising 20 cases each of coronary artery bypass grafting (CABG), mitral valve repair, and aortic valve replacement. The patient cohort was divided into two groups-30 patients whose CPB circuits were coated with phosphorylcholine (phosphorylcholine-coated group) and 30 patients who did not receive phosphorylcholine supplementation or circuit coating. Both groups underwent surgery with identical CPB circuit designs. We assessed the absence of adverse events, safety, and efficacy parameters, including blood loss, clotting, and the structural integrity of the CPB circuit. Additionally, we measured changes in mean albumin levels (g/dL), mean platelet counts (×109/L), and antithrombin III (ATIII) levels before and after CPB.

RESULTS

The retrospective analysis revealed an absence of adverse events in both groups. In the phosphorylcholine-coated group compared to the non-phosphorylcholine-coated group, there was a notable difference in the delta change in mean albumin levels (0.87 ± 0.1 vs. 1.65 ± 0.2 g/dL, p-value 0.021), mean platelet counts (42.251 ± 0.121 vs. 54.21 ± 0.194 × 109/L, p-value 0.049), and ATIII levels (16.85 ± 0.2 vs. 31.21 ± 0.3 p-value 0.017). There was a notable reduction in the perioperative consumption of human complex units after CPB (3 vs. 12, p-value 0.019).

CONCLUSIONS

Both groups, phosphorylcholine and non-phosphorylcholine, demonstrated the absence of adverse events and that the systems are safe for iatrogenic complication. Our findings suggest that the use of phosphorylcholine coating on the CPB circuit, in the absence of supplementary phosphorylcholine, in cardiac surgery is associated with favorable changes in mean albumin levels, mean platelet counts, and ATIII levels. Further research is warranted to elucidate the full extent of phosphorylcholine's impact on patient outcomes and CPB circuit performance.

Reducing hydrophobic drug adsorption in an in-vitro extracorporeal membrane oxygenation model

Extracorporeal membrane oxygenation (ECMO) is a life-saving cardiopulmonary bypass technology for critically ill patients with heart and lung failure. Patients treated with ECMO receive a range of drugs that are used to treat underlying diseases and critical illnesses. However, the dosing guidelines for these drugs used in ECMO patients are unclear. Mortality rate for patients on ECMO exceeds 40% partly due to inaccurate dosing information, caused in part by the adsorption of drugs in the ECMO circuit and its components. These drugs range in hydrophobicity, electrostatic interactions, and pharmacokinetics. Propofol is commonly administered to ECMO patients and is known to have high adsorption rates to the circuit components due to its hydrophobicity. To reduce adsorption onto the circuit components, we used micellar block copolymers (Poloxamer 188TM and Poloxamer 407TM) and liposomes tethered with poly(ethylene glycol) to encapsulate propofol, provide a hydrophilic shell and prevent its adsorption. Size, polydispersity index (PDI), and zeta potential of the delivery systems were characterized by dynamic light scattering, and encapsulation efficiency was characterized using High Performance Liquid Chromatography (HPLC). All delivery systems used demonstrated colloidal stability at physiological conditions for seven days, cytocompatibility with a human leukemia monocytic cell line, i.e., THP-1 cells, and did not activate the complement pathway in human plasma. We demonstrated a significant reduction in adsorption of propofol in an in-vitro ECMO model upon encapsulation in micelles and liposomes. These results show promise in reducing the adsorption of hydrophobic drugs to the ECMO circuits by encapsulation in nanoscale structures tethered with hydrophilic polymers on the surface.

Challenge of material haemocompatibility for microfluidic blood-contacting applications

Biological applications of microfluidics technology is beginning to expand beyond the original focus of diagnostics, analytics and organ-on-chip devices. There is a growing interest in the development of microfluidic devices for therapeutic treatments, such as extra-corporeal haemodialysis and oxygenation. However, the great potential in this area comes with great challenges. Haemocompatibility of materials has long been a concern for blood-contacting medical devices, and microfluidic devices are no exception. The small channel size, high surface area to volume ratio and dynamic conditions integral to microchannels contribute to the blood-material interactions. This review will begin by describing features of microfluidic technology with a focus on blood-contacting applications. Material haemocompatibility will be discussed in the context of interactions with blood components, from the initial absorption of plasma proteins to the activation of cells and factors, and the contribution of these interactions to the coagulation cascade and thrombogenesis. Reference will be made to the testing requirements for medical devices in contact with blood, set out by International Standards in ISO 10993-4. Finally, we will review the techniques for improving microfluidic channel haemocompatibility through material surface modifications-including bioactive and biopassive coatings-and future directions.

Zwitterionic Polysulfobetaine Coating and Antiplatelet Liposomes Reduce Fouling in Artificial Lung Circuits

The artificial lung has provided life-saving support for pulmonary disease patients and recently afforded patients with severe cases of COVID-19 better prognostic outcomes. While it addresses a critical medical need, reducing the risk of clotting inside the device remains challenging. Herein, a two-step surface coating process of the lung circuit using Zwitterionic polysulfobetaine methacrylate is evaluated for its nonspecific protein antifouling activity. It is hypothesized that similarly applied coatings on materials integrated (IT) or nonintegrated (NIT) into the circuit will yield similar antifouling activity. The effects of human plasma preconditioned with nitric oxide-loaded liposome on platelet (plt) fouling are also evaluated. Fibrinogen antifouling activities in coated fibers are similar in the IT and NIT groups. It however decreases in coated polycarbonate (PC) in the IT group. Also, plt antifouling activity in coated fibers is similar in the IT and NIT groups and is lower in coated PC and Tygon in the IT group compared to the NIT group. Coating process optimization in the IT lung circuit may help address difference in the coating appearance of outer and inner fiber bundle fibers, and the NO-liposome significantly reduces (86%) plt fouling on fibers indicating its potential use for blood anticoagulation.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Recent developments in polynorepinephrine: an innovative material for bioinspired coatings and colloids

While applications of polydopamine (PDA) are exponentially growing, research concerning the closely related neurotransmitter derivative polynorepinephrine (PNE) is in paucity, even though norepinephrine shares dopamine's ability to self-polymerize and form a coating film that is nearly substrate-agnostic. In this review, we demonstrate that PNE can be used as an alternative to PDA with equal or ever superior performance. PNE offers a thinner and smoother coating surface and thus is capable of more effectively resisting fouling by biofoulants, enhancing cell adhesion capability, surface hydrophilicity and biomolecule immobilisation. With the abundance of catechol, amino and hydroxyl groups in PNE's structure, PNE can perform as an electron donor and receiver at the same time and initiate ring opening and redox reactions. It has also been shown that PNE has the potential to be used as a biosensor due to its bioconjugation and molecular recognition ability. Here, we summarise the applications of PNE to date and discuss its potential research directions in the near future.

Bleeding During Veno-Venous ECMO: Prevention and Treatment

Veno-venous extracorporeal membrane oxygenation (vvECMO) has become a routine treatment for severe lung failure in specialized centers. Spontaneous bleeding complications, however, are observed in 30–60% of patients during vvECMO treatment. Bleeding increases mortality by factors 2–3. Anticoagulation in combination with several acquired bleeding disorders caused by the mechanical pump and the foreign layer of the extracorporeal system contribute to the risk of bleeding. In this review, the mechanisms of the underlying pathologies and the route from diagnosis to treatment are described.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

The horizon of pediatric cardiac critical care

Pediatric Cardiac Critical Care (PCCC) is a challenging discipline where decisions require a high degree of preparation and clinical expertise. In the modern era, outcomes of neonates and children with congenital heart defects have dramatically improved, largely by transformative technologies and an expanding collection of pharmacotherapies. Exponential advances in science and technology are occurring at a breathtaking rate, and applying these advances to the PCCC patient is essential to further advancing the science and practice of the field. In this article, we identified and elaborate on seven key elements within the PCCC that will pave the way for the future.

New Trends, Advantages and Disadvantages in Anticoagulation and Coating Methods Used in Extracorporeal Life Support Devices

The use of extracorporeal life support (ECLS) devices has significantly increased in the last decades. Despite medical and technological advancements, a main challenge in the ECLS field remains the complex interaction between the human body, blood, and artificial materials. Indeed, blood exposure to artificial surfaces generates an unbalanced activation of the coagulation cascade, leading to hemorrhagic and thrombotic events. Over time, several anticoagulation and coatings methods have been introduced to address this problem. This narrative review summarizes trends, advantages, and disadvantages of anticoagulation and coating methods used in the ECLS field. Evidence was collected through a PubMed search and reference scanning. A group of experts was convened to openly discuss the retrieved references. Clinical practice in ECLS is still based on the large use of unfractionated heparin and, as an alternative in case of contraindications, nafamostat mesilate, bivalirudin, and argatroban. Other anticoagulation methods are under investigation, but none is about to enter the clinical routine. From an engineering point of view, material modifications have focused on commercially available biomimetic and biopassive surfaces and on the development of endothelialized surfaces. Biocompatible and bio-hybrid materials not requiring combined systemic anticoagulation should be the future goal, but intense efforts are still required to fulfill this purpose.

Toward an artificial endothelium: Development of blood-compatible surfaces for extracorporeal life support

A new generation of extracorporeal artificial organ support technologies, collectively known as extracorporeal life support (ECLS) devices, is being developed for diverse applications to include acute support for trauma-induced organ failure, transitional support for bridge to organ transplant, and terminal support for chronic diseases. Across applications, one significant complication limits the use of these life-saving devices: thrombosis, bleeding, and inflammation caused by foreign surface-induced blood interactions. To address this challenge, transdisciplinary scientists and clinicians look to the vascular endothelium as inspiration for development of new biocompatible materials for ECLS. Here, we describe clinically approved and new investigational biomaterial solutions for thrombosis, such as immobilized heparin, nitric oxide-functionalized polymers, "slippery" nonadhesive coatings, and surface endothelialization. We describe how hemocompatible materials could abrogate the use of anticoagulant drugs during ECLS and by doing so radically change treatments in critical care. Additionally, we examine several special considerations for the design of biomaterials for ECLS, including: (1) preserving function of the artificial organ, (2) longevity of use, and (3) multifaceted approaches for the diversity of device functions and applications.

Hematologic concerns in extracorporeal membrane oxygenation

This ISTH "State of the Art" review aims to critically evaluate the hematologic considerations and complications in extracorporeal membrane oxygenation (ECMO). ECMO is experiencing a rapid increase in clinical use, but many questions remain unanswered. The existing literature does not address or explicitly state many pertinent details that may influence hematologic complications and, ultimately, patient outcomes. This review aims to broadly introduce modern ECMO practices, circuit designs, circuit materials, hematologic complications, transfusion-related considerations, age- and size-related differences, and considerations for choosing outcome measures. Relevant studies from the 2019 ISTH Congress in Melbourne, which further advanced our understanding of these processes, will also be highlighted.

The influence of cerebrospinal fluid on blood coagulation and the implications for ventriculovenous shunting

OBJECTIVE

The effect of CSF on blood coagulation is not known. Enhanced coagulation by CSF may be an issue in thrombotic complications of ventriculoatrial and ventriculosinus shunts. This study aimed to assess the effect of CSF on coagulation and its potential effect on thrombotic events affecting ventriculovenous shunts.

METHODS

Two complementary experiments were performed. In a static experiment, the effect on coagulation of different CSF mixtures was evaluated using a viscoelastic coagulation monitor. A dynamic experiment confirmed the amount of clot formation on the shunt surface in a roller pump model.

RESULTS

CSF concentrations of 9% and higher significantly decreased the activated clotting time (ACT; 164.9 seconds at 0% CSF, 155.6 seconds at 9% CSF, and 145.1 seconds at 32% CSF). Increased clot rates (CRs) were observed starting at a concentration of 5% (29.3 U/min at 0% CSF, 31.6 U/min at 5% CSF, and 35.3 U/min at 32% CSF). The roller pump model showed a significantly greater percentage of shunt surface covered with deposits when the shunts were infused with CSF rather than Ringer's lactate solution (90% vs 63%). The amount of clot formation at the side facing the blood flow (impact side) tended to be lower than that at the side facing away from the blood flow (wake side; 71% vs 86%).

CONCLUSIONS

Addition of CSF to blood accelerates coagulation. The CSF-blood-foreign material interaction promotes clot formation, which might result in thrombotic shunt complications. Further development of the ventriculovenous shunt technique should focus on preventing CSF-blood-foreign material interaction and stagnation of CSF in wake zones.

Novel Surfaces in Extracorporeal Membrane Oxygenation Circuits

The balance between systemic anticoagulation and clotting is challenging. In normal hemostasis, the endothelium regulates the balance between anticoagulant and prothrombotic systems. It becomes particularly more challenging to maintain this physiologic hemostasis when we are faced with extracorporeal life support therapies, where blood is continuously in contact with a foreign extracorporeal circuit surface predisposing a prothrombotic state. The blood-surface interaction during extracorporeal life support therapies requires the use of systemic anticoagulation to decrease the risk of clotting. Unfractionated heparin is the most common anticoagulant agent widely used in this setting. New trends include the use of direct thrombin inhibitor agents for systemic anticoagulation; and surface modifications that aim to overcome the blood-biomaterial surface interaction by modifying the hydrophilicity or hydrophobicity of the polymer surface; and coating the circuit with substances that will mimic the endothelium or anti-thrombotic agents. To improve hemocompatibility in an extracorporeal circuit, replication of the anti-thrombotic and anti-inflammatory properties of the endothelium is ideal. Surface modifications can be classified into three major groups: biomimetic surfaces (heparin, nitric oxide, and direct thrombin inhibitors); biopassive surfaces [phosphorylcholine, albumin, and poly- 2-methoxyethylacrylate]; and endothelialization of blood contacting surface. The focus of this paper will be to review both present and future novel surface modifications that can obviate the need for systemic anticoagulation during extracorporeal life support therapies.

VV extracorporeal life support for the Third Millennium: will we need anticoagulation?

Since the late 1600's medicine and science have entertained the idea of extracorporeal circulation. With this technology to allow for cardiac and pulmonary support came the development of anticoagulation. Although this advanced the technology and capabilities of extracorporeal life support, it was not without complications and risks. The most common complications in extracorporeal life support (ECLS) present day are related to hemorrhage and thrombus due to the need for systemic anticoagulation and the challenges associated with it. This review focuses on present day techniques for anticoagulation for ECLS and what future surface modifications may do to obviate the use of systemic anticoagulation entirely.

Drugs pharmacokinetics during veno-venous extracorporeal membrane oxygenation in pediatrics

Data evaluating pharmacokinetic/pharmacodynamic (PK/PD) aspect in the pediatric population are scarce especially regarding the pediatric intensive care unit. Dosing of frequently used drugs (sedatives, analgesics, antibiotics and cardiovascular drugs) are mainly based on non "pediatric intensive care unit (PICU)" patients, and sometimes are translated from adult patients. Among PICU patients, the most complex patients are the ones who are critically ill and are receiving mechanical circulatory/respiratory support for cardiac and/or respiratory failure. The use of extracorporeal membrane oxygenation is associated with major PK and PD changes, especially in neonates and children. The objective of this review is to assess the current literature for pediatric PK data in patients receiving extracorporeal membrane oxygenation (ECMO).

Reduced Systemic Heparin Dose with Phosphorylcholine Coated Closed Circuit in Coronary Operations

In this prospective cohort study we addressed the clinical impact of a reduced anticoagulation protocol on the hospital outcome of patients undergoing coronary revascularization with cardiopulmonary bypass.

364 consecutive low to moderate risk patients scheduled for elective isolated coronary operations were admitted to the study. 184 patients (Control Group) received conventional open circuits and full systemic anticoagulation (target activated clotting time 480 seconds); 180 patients (Intraoperative ECMO group) received closed, phosphorylcholine coated circuits and a reduced systemic heparin dose (target activated clotting time 320 seconds).

Patients of the Intraoperative ECMO group had less requirement for allogeneic blood products (odds ratio 0.55, 95% confidence interval 0.34–0.92, p= 0.02), a significant containment of blood loss (374 ± 278 mL vs. 463 ± 321 mL in Control group, p= 0.005) a lower postoperative peak serum creatinine levels (1.19 ± 0.48 mg/dL vs. 1.41 ± 0.94 mg/dL in Control group, p= 0.048), and a significant lower rate of severe morbidity (odds ratio 0.27, 95% confidence interval 0.09–0.81, p= 0.02). A reduction of systemic anticoagulation is feasible with a non-heparin-bonded, closed biocompatible circuit, and results in a significant improvement of the outcome of low to moderate risk coronary patients.

The inflammatory response to cardiopulmonary bypass: a therapeutic overview

The demographic of cardiac surgery patients continues to evolve to include older, sicker candidates, all the while maintaining an expectation of excellent outcomes. These latter results can only be achieved by the parallel advancement and re-examination of the technology of cardiopulmonary bypass (CPB); the key tool used daily by surgical teams worldwide. In this review, we will provide an overview of integrated therapeutic strategies that can be utilized to minimize the complex and myriad changes related to inflammation after CPB with the understanding that this may abrogate the detrimental end-organ and systemic effects of blood activation. Therapeutic strategies specifically related to the technology can be classified into those targeting biomaterial dependent or independent processes. The former can be addressed by the utilization of currently available biocompatible surfaces such as with heparin-coated circuits, phosphorylcholine-coated circuits (‘biomembrane mimicry’) and circuits composed of copolymers containing surface-modifying additives. The most important strategies related to biomaterial independent activation include the modification of techniques related to cardiotomy blood management and blood filtration. Finally, all of these strategies must be integrated and tailored with complementary pharmacologic agents such as aprotinin and steroids to optimize anti-inflammatory synergism. Only if we are armed with a comprehensive knowledge of the molecular and cellular basis for these strategies will we be able to continue to evolve our treatment in parallel with our patients to achieve these goals.

Clinical significance of coated extracorporeal circuits: a review of novel technologies

Coating of extracorporeal circuits may be a solution to prevent adverse effects induced by the contact of blood elements and proteins with foreign surfaces. This paper reviews the recent novel coating technologies and compares their documented in vitro and ex vivo advantages under the clinical setting. Data presented have also been supported by postclinical biomaterial research to verify biocompatibility and hemocompatibility.

Humoral immune response and coated or uncoated oxygenators during cardiopulmonary bypass surgery

Aim:

To investigate and compare uncoated and phosphorylcholine-coated oxygenators in terms of induction of humoral immune response during coronary artery bypass surgery.

Methods:

A total of 20 consecutive patients who underwent coronary artery bypass surgery were randomly distributed into two groups according to the type of oxygenator used during surgery. Group 1 consisted of 10 patients who were operated on using phosphorylcholine-coated oxygenators. Group 2 contained 10 patients who underwent surgery using uncoated oxygenators. Blood and oxygenator fibre samples were obtained and compared in terms of immunoglobulins (IgG, IgM), complements (C3c, C4), serum total protein and albumin levels using electron microscopy and flow cytometry.

Results:

In group 1, levels of IgM, IgG, total protein and serum albumin were significantly increased at the end of cardiopulmonary bypass (CPB) compared to those at the beginning of CPB. In group 2, C3c and C4 levels at the beginning of CPB were found to be significantly higher than at the end. Electron microscopic examination of oxygenator fibres demonstrated that phosphorylcholine-coated fibres were less likely to be adsorbed by serum proteins and complements than the uncoated fibres.

Conclusion:

Our results indicate that phosphorylcholine-coated oxygenators seemed to induce humoral immune response to a lesser extent than uncoated oxygenators during coronary artery bypass procedures.

Effects of conventional CPB and mini-CPB on neutrophils CD162, CD166 and CD195 expression

OBJECTIVE

Cardiac surgery is known to trigger a systemic inflammatory response. While the use of conventional cardiopulmonary bypass (CPB) results in profound inflammation, modified mini-CPB is considered less harmful. We evaluated the impact of cardiac surgery on the expression of CD162, CD166, CD195 molecules and their association with the type of CPB used.

METHODS AND RESULTS

Twenty-four patients were enrolled in our study. Twelve of them were operated using conventional CPB while the other twelve patients underwent surgery with mini-CPB. Blood samples were analysed by flow cytometry. We observed a significant increase in median fluorescence intensity of CD162 and CD195 that peaked instantly after surgery and normalized to the baseline value on the 1^st day post surgery, whereas CD166 was initially down-regulated and its median fluorescence intensity (MFI) value increased to the baseline in the next few days.

CONCLUSION

We observed immediate changes in the expression of CD162, CD166, and CD195 molecules on the neutrophils after surgery in both study groups of patients. The intensity of the observed changes was significantly greater in the group of patients who underwent conventional CPB compared to patients who underwent mini-CPB cardiac surgery.

Pharmacokinetics and Dosing of Anti-infective Drugs in Patients on Extracorporeal Membrane Oxygenation: A Review of the Current Literature

PURPOSE

Extracorporeal membrane oxygenation (ECMO) is a cardiopulmonary bypass device that is used to temporarily support the most critically ill of patients with respiratory and/or cardiac failure. Infection and its sequelae may be an indication for ECMO or infections may be acquired while on ECMO and are associated with a mortality >50%. Effective therapy requires optimal dosing. However, optimal dosing can be different in patients on ECMO because the ECMO circuit can alter drug pharmacokinetics. This review assessed the current literature for pharmacokinetic data and subsequent dosing recommendations for anti-infective drugs in patients on ECMO.

METHODS

We searched the PubMed and Embase databases (1965 to February 2016) and included case reports, case series, or studies that provided pharmacokinetic data for anti-infective drugs including antibiotics, antifungals, and antivirals being used to treat patients of all age groups on ECMO. Pharmacokinetic parameters and dosing recommendations based on these data are presented.

FINDINGS

The majority of data on this topic comes from neonatal studies of antibiotics from the 1980s and 1990s. These studies generally demonstrate a larger volume of distribution due to ECMO and therefore higher doses are needed initially. More adult data are now emerging, but with a predominance of case reports and case series without comparison with critically ill controls. The available pharmacokinetic analyses do suggest that volume of distribution and clearance are unchanged in the adult population, and therefore dosing recommendations largely remain unchanged. There is a lack of data on children older than 1 year of age. The data support the importance of therapeutic drug monitoring when available in this population of patients.

IMPLICATIONS

This review found reasonably robust dosing recommendations for some drugs and scant or no data for other important anti-infectives. In order to better determine optimal dosing for patients on ECMO, a systematic approach is needed. Approaches that combine ex vivo ECMO experiments, animal studies, specialized pharmacokinetic modeling, and human clinical trials are being developed.

Significantly reduced adsorption and activation of blood components in a membrane oxygenator system coated with crosslinkable zwitterionic copolymer

A crosslinkable zwitterionic copolymer PMBT was coated onto the surfaces of polypropylene hollow fiber membrane (PP-HFM) oxygenator and its connecting tubes. The PMBT copolymer coating on the oxygenator circuit formed a cell outer membrane mimetic surface with excellent stability. The hemocompatibility of the PMBT copolymer coated PP-HFM oxygenator circuit was evaluated by animal extracorporeal circulation. The concentrations of clotting components fibrinogen and platelet in the blood were almost unchanged during the circulation through the PMBT copolymer coated oxygenator circuits. By contrast, the concentrations of fibrinogen and platelet were significantly reduced to 52% and 56% respectively in the uncoated oxygenator group due to adsorption and thrombogenesis of the blood during 2h circulation. Moreover, concentration of activation marker beta-thromboglobulin for platelet in the blood was remarkably lower in the PMBT group than the uncoated control group (p<0.01). All the results strongly supported that the hemocompatibility of the PP-HFM oxygenator circuit could be improved significantly by coating a stable and densely assembled zwitterionic polymer film. This simple, stable and highly effective cell membrane mimetic coating strategy may be applicable in developing advanced oxygenator systems and other artificial organs.

STATEMENT OF SIGNIFICANCE

Although a number of studies have reported the fabrication of zwitterionic phosphorylcholine coated oxygenators to resist the adsorption and activation of blood components and eliminate heparin-induced thrombocytopenia, none of them have fabricated stable and densely assembled film, especially with crosslinkable amphiphilic random copolymer described in our manuscript. The novel features of our work include.

Stirred, shaken, or stagnant: What goes on at the blood-biomaterial interface

There is a widely recognized need to improve the performance of vascular implants and external medical devices that come into contact with blood by reducing adverse reactions they cause, such as thrombosis and inflammation. These reactions lead to major adverse cardiovascular events such as heart attacks and strokes. Currently, they are managed therapeutically. This need remains unmet by the biomaterials research community. Recognized stagnation of the blood-biomaterial interface research translates into waning interest from clinicians, funding agencies, and practitioners of adjacent fields. The purpose of this contribution is to stir things up. It follows the 2014 BloodSurf meeting (74th International IUVSTA Workshop on Blood-Biomaterial Interactions), offers reflections on the situation in the field, and a three-pronged strategy integrating different perspectives on the biological mechanisms underlying blood-biomaterial interactions. The success of this strategy depends on reengaging clinicians and on the renewed cooperation of the funding agencies to support long-term efforts.

Evaluation of coated oxygenators in cardiopulmonary bypass systems and their impact on neurocognitive function

Introduction: Coronary artery bypass graft surgery (CABG) using cardiopulmonary bypass (CPB) is assumed to be associated with a decline of neurocognitive functions. This study was designed to analyse the neurocognitive function of patients with coronary heart disease before and after CABG and to determine possible protective effects of oxygenator surface coating on neurological outcome.

Methods: Forty patients scheduled for selective CABG were prospectively randomized into two groups of 20 patients each according to the type of hollow-fibre membrane oxygenator used. Non-coated oxygenators (Group A) were compared to phosphorylcholine (PC)- coated oxygenators (Group B). A battery of six neurological tests was administered preoperatively, 7 - 10 days and 4 - 6 months after surgery.

Results: One patient of Group A suffered from a perioperative stroke and died on postoperative day 3, presumably because of sudden heart failure. Two patients of Group A (10%) developed a symptomatic transitory delirious psychotic syndrome (STPT) on postoperative days 3 and 5. None of the patients of Group B had perioperative complications. The test analysis revealed a trend of declined neurocognitive function early after CABG, but did not show any difference in neurocognitive outcome between the two groups.

Discussion: PC coating of the oxygenators did not show any significant benefit on neurocognitive function after CABG using CPB.

Pulmonary complications of cardiopulmonary bypass

Pulmonary complications after the use of extracorporeal circulation are common, and they range from transient hypoxemia with altered gas exchange to acute respiratory distress syndrome (ARDS), with variable severity. Similar to other end-organ dysfunction after cardiac surgery with extracorporeal circulation, pulmonary complications are attributed to the inflammatory response, ischemia-reperfusion injury, and reactive oxygen species liberated as a result of cardiopulmonary bypass. Several factors common in cardiac surgery with extracorporeal circulation may worsen the risk of pulmonary complications including atelectasis, transfusion requirement, older age, heart failure, emergency surgery, and prolonged duration of bypass. There is no magic bullet to prevent or treat pulmonary complications, but supportive care with protective ventilation is important. Targets for the prevention of pulmonary complications include mechanical, surgical, and anesthetic interventions that aim to reduce the contact activation, systemic inflammatory response, leukocyte sequestration, and hemodilution associated with extracorporeal circulation.

Oxygenator Is the Main Responsible for Leukocyte Activation in Experimental Model of Extracorporeal Circulation: A Cautionary Tale

In order to assess mechanisms underlying inflammatory activation during extracorporeal circulation (ECC), several small animal models of ECC have been proposed recently. The majority of them are based on home-made, nonstandardized, and hardly reproducible oxygenators. The present study has generated fundamental information on the role of oxygenator of ECC in activating inflammatory signaling pathways on leukocytes, leading to systemic inflammatory response, and organ dysfunction. The present results suggest that experimental animal models of ECC used in translational research on inflammatory response should be based on standardized, reproducible oxygenators with clinical characteristics.

Heparin-coated cardiopulmonary bypass circuits selectively deplete the pattern recognition molecule ficolin-2 of the lectin complement pathway in vivo

The complement system can be activated via the lectin pathway by the recognition molecules mannose-binding lectin (MBL) and the ficolins. Ficolin-2 exhibits binding against a broad range of ligands, including biomaterials in vitro, and low ficolin-2 levels are associated with increased risk of infections. Thus, we investigated the biocompatibility of the recognition molecules of the lectin pathway in two different types of cardiopulmonary bypass circuits. Bloods were drawn at five time-points before, during and postoperatively from 30 patients undergoing elective cardiac surgery. Patients were randomized into two groups using different coatings of cardiopulmonary bypass circuits, Phisio® (phosphorylcholine polymer coating) and Bioline® (albumin-heparin coating). Concentrations of MBL, ficolin-1, -2 and -3 and soluble C3a and terminal complement complex (TCC) in plasma samples were measured. Ficolin-3-mediated complement activation potential was evaluated with C4, C3 and TCC as output. There was no significant difference between the two circuit materials regarding MBL, ficolin-1 and -3. In the Bioline® group the ficolin-2 levels decreased significantly after initiation of surgery (P < 0.0001) and remained reduced throughout the sampling period. This was not seen for Phisio®-coated circuits. Ficolin-3-mediated complement activation potential was reduced significantly in both groups after start of operation (P < 0.0001), whereas soluble C3a and TCC in the samples were increased (P < 0.0001). Ficolin-2 was depleted from plasma during cardiac surgery when using heparin-coated bypass circuits and did not reach baseline level 24 h postoperation. These findings may have implications for the postoperative susceptibility to infections in patients undergoing extracorporeal circulation procedures.

Efficiency of gas transfer in venovenous extracorporeal membrane oxygenation: analysis of 317 cases with four different ECMO systems

PURPOSE

Polymethylpentene membrane oxygenators used in venovenous extracorporeal membrane oxygenation (vvECMO) differ in their physical characteristics. The aim of the study was to analyze the gas transfer capability of different ECMO systems in clinical practice, as the choice of the appropriate system may be influenced by the needs of the patient.

METHODS

Retrospective study on prospectively collected data of adults with severe respiratory failure requiring vvECMO support (Regensburg ECMO Registry, 2009-2013). Oxygen (O2) transfer and carbon dioxide (CO2) elimination of four different ECMO systems (PLS system, n = 163; Cardiohelp system (CH), n = 59, Maquet Cardiopulmonary, Rastatt, Germany; Hilite 7000 LT system, n = 56, Medos Medizintechnik, Stolberg, Germany; ECC.05 system, n = 39, Sorin Group, Mirandola (MO), Italy) were analyzed.

RESULTS

Gas transfer depended on type of ECMO system, blood flow, and gas flow (p ≤ 0.05, each). CO2 removal is dependent on sweep gas flow and blood flow, with higher blood flow and/or gas flow eliminating more CO2 (p ≤ 0.001). CO2 elimination capacity was highest with the PLS system (p ≤ 0.001). O2 transfer at blood flow rates below 3 l/min depended on blood flow, at higher blood flow rates on blood flow and gas flow. The system with the smallest gas exchange surface (ECC.05 system) was least effective in O2 transfer, but in terms of the gas exchange surface was the most effective.

CONCLUSION

Our analysis suggests that patients with severe hypoxemia and need for high flow ECMO benefit more from the PLS/CH or Hilite 7000 LT system. The ECC.05 system is advisable for patients with moderate hypoxemia and/or hypercapnia.

Currently available biomaterials for use in cardiopulmonary bypass

Cardiopulmonary bypass (CPB) represents one of the most important technical innovations in healthcare history, yet the systemic responses to CPB remain a fundamentally unresolved problem. Study of the blood-biomaterial interaction and development of biocompatible materials is intimately related to efforts to optimize patient outcome following CPB. This article reviews the design innovations in biomaterial surfaces that have been introduced into clinical practice in an attempt to ameliorate the detrimental consequences of CPB, contrasting the actual clinical improvements and patient benefits achieved against those predicted on the basis of theory and in vitro testing. Some discussion of the underlying mechanisms of action as presently understood is provided and the current limitations of biomaterial-dependent strategies to improve outcome following CPB are addressed.

Excessive negative venous line pressures and increased arterial air bubble counts during miniaturized cardiopulmonary bypass: an experimental study comparing miniaturized with conventional perfusion systems

OBJECTIVES

Miniaturized cardiopulmonary bypass (MCPB) is increasingly used in cardiac surgery, because it can lower clinically significant complications such as systemic inflammatory response, haemolysis and high transfusion requirements. A limitation of MCPB is the risk of excessive negative pressure in the venous line during volume depletion, probably leading to gaseous microembolism.

METHODS

In an experimental study with 24 pigs, we compared conventional open cardiopulmonary bypass (CCPB group, n = 11) with MCPB (n = 13). The same pump and identical tubing materials were used in both groups. Primary endpoints were pressure values in the venous line and the right atrium as well as the amount of air bubbles >500 µm. Secondary endpoints were biochemical parameters of systemic inflammatory response, ischaemia, haemodilution and haemolysis.

RESULTS

Nearly 20% of venous pressure values were below -150 mmHg and approximately 10% of the right atrial pressure values were below -100 mmHg in the MCPB group, during the experiment. No such low values were observed in the CCPB group. In addition, the number of large arterial air bubbles was higher in the MCPB group compared with the CCPB group (mean ± standard deviation [SD]: 13 444 ± 5709 vs 0.9 ± 0.6, respectively; P < 0.001). Bubble volume was also significantly larger during MCPB compared with CCPB (mean ± SD: 1522 ± 654 vs 4.1 ± 2.5 µl, respectively; P < 0.001). Blood levels of interleukin-6, free haemoglobin and creatine kinase were significantly higher in the CCPB group compared with the MCPB group.

CONCLUSIONS

Despite the benefits of MCPB regarding systemic inflammatory response and haemolysis, this technique is associated with excessive negative venous line pressures and a significant increase in the number and volume of arterial air bubbles compared with CCPB. Mini-perfusion systems and the management of MCPB require further refinements to avoid such adverse effects.

Comparable biocompatibility of Phisio- and Bioline-coated cardiopulmonary bypass circuits indicated by the inflammatory response

Background: The biocompatibility of cardiopulmonary bypass surfaces has been improved by heparin and polymer surface modifications. The present study compared the effect of two such coatings on the inflammatory reactions after open heart surgery.

Methods:Thirty patients undergoing elective heart surgery were randomly assigned to receive one of two types of coated circuits: Bioline (n=15) or phosphorylcholine (Phisio, n=15). The platelet and leukocyte counts, neutrophil activation (myeloperoxidase), complement activation (C3a and TCC), concentrations of lactate dehydrogenase, 27 cytokines (including interleukins, chemokines and growth factors), thrombin-antithrombin complexes, and the endothelial cell marker syndecan-1 were analyzed at five predetermined time points until 24 hrs post operatively.

Results: Most measurements were comparable in both groups. However, myeloperoxidase was significantly higher in the Bioline group (p < 0.001). Postoperative lactate dehydrogenase concentrations were significantly higher in the Phisio group (p<0.01) and the maximal concentration of thrombin-antithrombin complexes 2 hours postoperatively tended to be higher in the Phisio group (p=0.08), consistent with a longer aortic cross-clamp and cardiopulmonary bypass time. Conclusions: The two circuits exhibited a comparable degree of in vivo biocompatibility.

Strategies to prevent intraoperative lung injury during cardiopulmonary bypass

During open heart surgery the influence of a series of factors such as cardiopulmonary bypass (CPB), hypothermia, operation and anaesthesia, as well as medication and transfusion can cause a diffuse trauma in the lungs. This injury leads mostly to a postoperative interstitial pulmonary oedema and abnormal gas exchange. Substantial improvements in all of the above mentioned factors may lead to a better lung function postoperatively. By avoiding CPB, reducing its time, or by minimizing the extracorporeal surface area with the use of miniaturized circuits of CPB, beneficial effects on lung function are reported. In addition, replacement of circuit surface with biocompatible surfaces like heparin-coated, and material-independent sources of blood activation, a better postoperative lung function is observed. Meticulous myocardial protection by using hypothermia and cardioplegia methods during ischemia and reperfusion remain one of the cornerstones of postoperative lung function. The partial restoration of pulmonary artery perfusion during CPB possibly contributes to prevent pulmonary ischemia and lung dysfunction. Using medication such as corticosteroids and aprotinin, which protect the lungs during CPB, and leukocyte depletion filters for operations expected to exceed 90 minutes in CPB-time appear to be protective against the toxic impact of CPB in the lungs. The newer methods of ultrafiltration used to scavenge pro-inflammatory factors seem to be protective for the lung function. In a similar way, reducing the use of cardiotomy suction device, as well as the contact-time between free blood and pericardium, it is expected that the postoperative lung function will be improved.

Initial clinical experience with the admiral oxygenator combined with separated suction

The Admiral, a new microporous membrane oxygenator with a low surface area, decreased priming volume and two separate reservoirs, was tested in 30 adult patients. This study was undertaken to evaluate blood path resistance, gas exchange capabilities and blood trauma in clinical use, with and without shed blood separation. Patients were divided into 3 groups. Group 1 had valve surgery without separation of suction, Group 2 had coronary artery bypass grafting (CABG) with direct blood aspiration and Group 3 had coronary artery bypass grafting with shed blood separation. The suctioned, separated, cardiotomy blood in Group 3 was treated with an autotransfusion device at the end of bypass before being returned to the patient. Theoretical blood flow could be achieved in all cases without problem. The pressure drop through the oxygenator averaged 88 +/- 13 mmHg at 4 l/min and 109 +/- 12 mmHg at 5 l/min. O(2) transfer was 163 +/- 27 ml/min. Free plasma haemoglobin rose in all groups, but significantly less in group 3. Lactate dehydrogenase (LDH) rose significantly in Groups 1 and 2. Platelets decreased in all groups without significant differences. Clinical experience with this new oxygenator was safe, the reduced membrane surface did not impair gas exchange and blood trauma could be minimized easily by separating shed blood, using the second cardiotomy reservoir.

Minimally invasive cardiopulmonary bypass: does it really change the outcome?

Introduction

Many innovative cardiopulmonary bypass (CPB) systems have recently been proposed by the industry. With few differences, they all share a philosophy based on priming volume reduction, closed circuit with separation of the surgical field suction, centrifugal pump, and biocompatible circuit and oxygenator. These minimally invasive CPB (MICPB) systems are intended to limit the deleterious effects of a conventional CPB. However, no evidence exists with respect to their effectiveness in improving the postoperative outcome in a large population of patients. This study aimed to verify the clinical impact of an MICPB in a large population of patients undergoing coronary artery revascularization.

Methods

We conducted a retrospective analysis of 1,663 patients treated with an MICPB. The control group (conventional CPB) was extracted from a series of 2,877 patients according to a propensity score analysis.

Results

Patients receiving an MICPB had a shorter intensive care unit (ICU) stay, had lower peak postoperative serum creatinine and bilirubin levels, and suffered less postoperative blood loss. Within a multivariable model, MICPB is independently associated with lower rates of atrial fibrillation (odds ratio [OR] 0.83, 95% confidence interval [CI] 0.69 to 0.99) and ventricular arrhythmias (OR 0.45, 95% CI 0.28 to 0.73) and with higher rates of early discharge from the ICU (OR 1.31, 95% CI 1.06 to 1.6) and from the hospital (OR 1.46, 95% CI 1.18 to 1.8). Hospital mortality did not differ between groups.

Conclusion

MICPBs are associated with reduced morbidity. However, these results will need to be confirmed in a large, prospective, randomized, controlled trial.

Renal function after cardiopulmonary bypass surgery in patients with impaired renal function. A randomized study of the effect of nifedipine

BACKGROUND AND OBJECTIVES

Postoperative acute renal failure predicts morbidity and mortality. We investigated the effect of nifedipine infusion on glomerular filtration rate in patients with impaired renal function undergoing cardiopulmonary bypass surgery.

METHODS

Twenty patients accepted for coronary bypass and/or heart valve surgery were enrolled prospectively and randomized to nifedipine infusion or no treatment. Males and females with creatinine 150 micromol L(-1) and 130 micromol L(-1), respectively, were included. Patients with unstable angina pectoris, ejection fraction 35% and those on dialysis were excluded. Glomerular filtration rate was measured preoperatively and 48 h postoperatively. Creatinine clearance was measured preoperatively and 0-4, 20-24 and 44-48 h postoperatively. There were no statistically significant differences in patient characteristics. Biochemical markers in plasma and urine were measured before and 48 h after surgery.

RESULTS

The mean +/- SD preoperative glomerular filtration rates were 32.2 +/- 11.5 and 31.4 +/- 17.0 mL min-1 per 1.73 m2 in the nifedipine and control groups (P = 0.90), respectively. There was no statistically significant change in the glomerular filtration rate or in creatinine clearance over time within or between groups. A linear mixed model showed no effect of nifedipine (P = 0.44), time (P = 0.97) or interaction of nifedipine and time (P = 0.99) on creatinine clearance. Perioperative arterial pressure was kept within predefined targets. Three patients received dialysis postoperatively, all in the control group (P = 0.21). There were no statistically significant differences between groups in changes of urinary or plasma biochemistry.

CONCLUSIONS

Renal function was well preserved after cardiopulmonary bypass surgery in patients with impaired renal function when maintaining thorough intensive care surveillance. Nifedipine did not influence early postoperative renal function.

Oxygenation?Ozonation of Blood During Extracorporeal Circulation: In Vitro Efficiency of a New Gas Exchange Device

We have investigated the performance of a new gas exchange device (GED), named L001, specifically devised for the ozonation of human blood during extracorporeal circulation. This procedure, defined with the acronym "EBOO," means "extracorporeal blood oxygenation-ozonation." The innovative GED is made of microporous, ozone-resistant, polipropylene hollow fibers with an external diameter of 200 microm, a thickness of 50 microm, and a membrane surface area of 0.22 m(2). The material is coated with phosphorylcholine on the external side in contact with the circulating blood, while a gas mixture, necessarily composed of medical oxygen and ozone (about 99 and 1%, respectively), flows inside the fibers in opposite direction. The new GED has been tested by using a buffered saline solution containing KI and by varying several parameters, and it has shown to be very versatile and efficient. Its main characteristics are minimal foreign surface contact, high gas transfer, and negligible priming volume. This device appears to be a practical, nontoxic, and rather inexpensive tool for performing ozonation of blood for already defined human diseases.