The science and practice of cardiopulmonary bypass: From cross circulation to ECMO and SIRS

Surgical pulmonary embolectomy on VA-ECMO

Surgical pulmonary embolectomy is a procedure that is often used to rescue patients with massive pulmonary embolism (PE) and circulatory collapse that have failed or may not be ideal candidates for other systemic and endovascular treatment modalities. This procedure typically involves a sternotomy and the use of cardiopulmonary bypass (CPB), which requires full systemic anticoagulation. Here, we report the case of a surgical pulmonary embolectomy performed on venoarterial extracorporeal membrane oxygenation (VA-ECMO) rather than CPB to minimize systemic anticoagulation. The patient had suffered a cardiac arrest due to a saddle PE and required VA-ECMO which was complicated by a concomitant intracranial hemorrhage. The patient tolerated the surgical pulmonary embolectomy performed on VA-ECMO without procedure-related complications, and the ECMO support did not substantially complicate the technical performance of the procedure. In contrast to surgical pulmonary embolectomy performed on CPB, greater attention must be paid to volume status when performing the procedure on VA-ECMO since there is no blood reservoir. This case suggests cardiopulmonary support on ECMO as a viable strategy for surgical embolectomy in patients with unstable PEs in whom thrombolysis or full systemic anticoagulation are contraindicated.

The Roles of Membrane Technology in Artificial Organs: Current Challenges and Perspectives

The recent outbreak of the COVID-19 pandemic in 2020 reasserted the necessity of artificial lung membrane technology to treat patients with acute lung failure. In addition, the aging world population inevitably leads to higher demand for better artificial organ (AO) devices. Membrane technology is the central component in many of the AO devices including lung, kidney, liver and pancreas. Although AO technology has improved significantly in the past few decades, the quality of life of organ failure patients is still poor and the technology must be improved further. Most of the current AO literature focuses on the treatment and the clinical use of AO, while the research on the membrane development aspect of AO is relatively scarce. One of the speculated reasons is the wide interdisciplinary spectrum of AO technology, ranging from biotechnology to polymer chemistry and process engineering. In this review, in order to facilitate the membrane aspects of the AO research, the roles of membrane technology in the AO devices, along with the current challenges, are summarized. This review shows that there is a clear need for better membranes in terms of biocompatibility, permselectivity, module design, and process configuration.

Intraoperative Oxygen Concentration and Neurocognition after Cardiac Surgery

BACKGROUND

Despite evidence suggesting detrimental effects of perioperative hyperoxia, hyperoxygenation remains commonplace in cardiac surgery. Hyperoxygenation may increase oxidative damage and neuronal injury leading to potential differences in postoperative neurocognition. Therefore, this study tested the primary hypothesis that intraoperative normoxia, as compared to hyperoxia, reduces postoperative cognitive dysfunction in older patients having cardiac surgery.

METHODS

A randomized double-blind trial was conducted in patients aged 65 yr or older having coronary artery bypass graft surgery with cardiopulmonary bypass. A total of 100 patients were randomized to one of two intraoperative oxygen delivery strategies. Normoxic patients (n = 50) received a minimum fraction of inspired oxygen of 0.35 to maintain a Pao2 above 70 mmHg before and after cardiopulmonary bypass and between 100 and 150 mmHg during cardiopulmonary bypass. Hyperoxic patients (n = 50) received a fraction of inspired oxygen of 1.0 throughout surgery, irrespective of Pao2 levels. The primary outcome was neurocognitive function measured on postoperative day 2 using the Telephonic Montreal Cognitive Assessment. Secondary outcomes included neurocognitive function at 1, 3, and 6 months, as well as postoperative delirium, mortality, and durations of mechanical ventilation, intensive care unit stay, and hospital stay.

RESULTS

The median age was 71 yr (interquartile range, 68 to 75), and the median baseline neurocognitive score was 17 (16 to 19). The median intraoperative Pao2 was 309 (285 to 352) mmHg in the hyperoxia group and 153 (133 to 168) mmHg in the normoxia group (P < 0.001). The median Telephonic Montreal Cognitive Assessment score on postoperative day 2 was 18 (16 to 20) in the hyperoxia group and 18 (14 to 20) in the normoxia group (P = 0.42). Neurocognitive function at 1, 3, and 6 months, as well as secondary outcomes, were not statistically different between groups.

CONCLUSIONS

In this randomized controlled trial, intraoperative normoxia did not reduce postoperative cognitive dysfunction when compared to intraoperative hyperoxia in older patients having cardiac surgery. Although the optimal intraoperative oxygenation strategy remains uncertain, the results indicate that intraoperative hyperoxia does not worsen postoperative cognition after cardiac surgery.

EDITOR’S PERSPECTIVE

Potential Consequences of the Red Blood Cell Storage Lesion on Cardiac Electrophysiology

Background The red blood cell (RBC) storage lesion is a series of morphological, functional, and metabolic changes that RBCs undergo following collection, processing, and refrigerated storage for clinical use. Since the biochemical attributes of the RBC unit shifts with time, transfusion of older blood products may contribute to cardiac complications, including hyperkalemia and cardiac arrest. We measured the direct effect of storage age on cardiac electrophysiology and compared it with hyperkalemia, a prominent biomarker of storage lesion severity. Methods and Results Donor RBCs were processed using standard blood-banking techniques. The supernatant was collected from RBC units, 7 to 50 days after donor collection, for evaluation using Langendorff-heart preparations (rat) or human induced pluripotent stem cell-derived cardiomyocytes. Cardiac parameters remained stable following exposure to "fresh" supernatant from red blood cell units (day 7: 5.8±0.2 mM K+), but older blood products (day 40: 9.3±0.3 mM K+) caused bradycardia (baseline: 279±5 versus day 40: 216±18 beats per minute), delayed sinus node recovery (baseline: 243±8 versus day 40: 354±23 ms), and increased the effective refractory period of the atrioventricular node (baseline: 77±2 versus day 40: 93±7 ms) and ventricle (baseline: 50±3 versus day 40: 98±10 ms) in perfused hearts. Beating rate was also slowed in human induced pluripotent stem cell-derived cardiomyocytes after exposure to older supernatant from red blood cell units (-75±9%, day 40 versus control). Similar effects on automaticity and electrical conduction were observed with hyperkalemia (10-12 mM K+). Conclusions This is the first study to demonstrate that "older" blood products directly impact cardiac electrophysiology, using experimental models. These effects are likely caused by biochemical alterations in the supernatant from red blood cell units that occur over time, including, but not limited to hyperkalemia. Patients receiving large volume and/or rapid transfusions may be sensitive to these effects.

Application of Piezo-Based Measuring System for Evaluation of Nucleic Acid-Based Drugs Influencing the Coagulation

During open-heart surgery, the status of hemostasis has to be constantly monitored to quickly and reliably detect bleeding or coagulation disorders. In this study, a novel optimized piezo-based measuring system (PIEZ) for rheological monitoring of hemostasis was established. The applicability of the PIEZ for the evaluation of nucleic acid-based drugs influencing coagulation was analyzed. Thrombin aptamers such as NU172 might be used during extracorporeal circulation (ECC) in combination with a reduced heparin concentration or for patients with heparin-induced thrombocytopenia (HIT). Therefore, the effect of the coagulation inhibiting thrombin aptamer NU172 and the abrogation by its complementary antidote sequence (AD) were investigated by this rheological PIEZ system. After the addition of different NU172 concentrations, the coagulation of fresh human blood was analyzed under static conditions and using an in vitro rotation model under dynamic conditions (simulating ECC). The clotting times (CTs) detected by PIEZ were compared to those obtained with a medical reference device, a ball coagulometer. Additionally, after the circulation of blood samples for 30 min at 37 °C, blood cell numbers, thrombin markers (thrombin-antithrombin III (TAT) and fibrinopeptide A (FPA)) and a platelet activation marker (β-thromboglobulin (β-TG)) were analyzed by enzyme-linked immunosorbent assays (ELISAs). The increase of NU172 concentration resulted in prolonged CTs, which were comparable between the reference ball coagulometer and the PIEZ, demonstrating the reliability of the new measuring system. Moreover, by looking at the slope of the linear regression of the viscous and elastic components, PIEZ also could provide information on the kinetics of the coagulation reaction. The shear viscosity at the end of the measurements (after 300 s) was indicative of clot firmness. Furthermore, the PIEZ was able to detect the abrogation of coagulation inhibition after the equimolar addition of NU172 aptamer´s AD. The obtained results showed that the established PIEZ is capable to dynamically measure the hemostasis status in whole blood and can be applied to analyze nucleic acid-based drugs influencing the coagulation.

Study Protocol for a Pilot, Open-Label, Prospective, and Observational Study to Evaluate the Pharmacokinetics of Drugs Administered to Patients during Extracorporeal Circulation; Potential of In Vivo Cytochrome P450 Phenotyping to Optimise Pharmacotherapy

Pharmacokinetic alterations of medications administered during surgeries involving cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO) have been reported. The impact of CPB on the cytochrome P450 (CYP) enzymes’ activity is the key factor. The metabolic rates of caffeine, dextromethorphan, midazolam, omeprazole, and Losartan to the CYP-specific metabolites are validated measures of in vivo CYP 1A2, 2D6, 3A4, 2C19, and 2C9 activities, respectively. The study aim is to assess the activities of major CYPs in patients on extracorporeal circulation (EC). This is a pilot, prospective, open-label, observational study in patients undergoing surgery using EC and patients undergoing laparoscopic cholecystectomy as a control group. CYP activities will be measured on the day, and 1–2 days pre-surgery/3–4 days post-surgery (cardiac surgery and Laparoscopic cholecystectomy) and 1–2 days after starting ECMO, 1–2 weeks after starting ECMO, and 1–2 days after discontinuation from ECMO. Aforementioned CYP substrates will be administered to the patient and blood samples will be collected at 0, 1, 2, 4, and 6 h post-dose. Major CYP enzymes’ activities will be compared in each participant on the day, and before/after surgery. The CYP activities will be compared in three study groups to investigate the impact of CYPs on EC.

A Computational Model of Heat Loss and Water Condensation on the Gas-Side of Blood Oxygenators

Clinical observation of condensation at the gas flow exit of blood oxygenators is a recurrent event during cardiopulmonary bypass. These devices consist of a bundle of hollow fibers made of a microporous membrane that allows the exchange of O₂ and CO₂. The fibers carry a gas mixture inside (intraluminal flow), while blood flows externally around them (extraluminal flow). Although different studies described this effect in the past, the specific role of the different sections of the device requires further analysis, and the total condensation rate remains unquantified. In this study, a closer look is taken at the transition of gas between the oxygenation bundle and the external room air. A method is proposed to estimate the total condensate output, combining computational fluid dynamics (CFD) of thermal distribution and a simplified 1D model of water vapor saturation of gas. The influence of a number of different parameters is analyzed, regarding material properties, environmental conditions, and clinical use. Results show that condensation rate could vary in a 30‐fold range within reasonably small variations of the different variables considered.

Combination of aptamer and drug for reversible anticoagulation in cardiopulmonary bypass

Unfractionated heparin (UFH), the standard anticoagulant for cardiopulmonary bypass (CPB) surgery, carries a risk of post-operative bleeding and is potentially harmful in patients with heparin-induced thrombocytopenia-associated antibodies. To improve the activity of an alternative anticoagulant, the RNA aptamer 11F7t, we solved X-ray crystal structures of the aptamer bound to factor Xa (FXa). The finding that 11F7t did not bind the catalytic site suggested that it could complement small-molecule FXa inhibitors. We demonstrate that combinations of 11F7t and catalytic-site FXa inhibitors enhance anticoagulation in purified reaction mixtures and plasma. Aptamer-drug combinations prevented clot formation as effectively as UFH in human blood circulated in an extracorporeal oxygenator circuit that mimicked CPB, while avoiding side effects of UFH. An antidote could promptly neutralize the anticoagulant effects of both FXa inhibitors. Our results suggest that drugs and aptamers with shared targets can be combined to exert more specific and potent effects than either agent alone.

[Value of indoleamine 2,3-dioxygenase in diagnosis of systemic inflammatory response syndrome after cardiopulmonary bypass in children with congenital heart disease]

OBJECTIVE

To study the value of indoleamine 2,3-dioxygenase (IDO) in the early diagnosis of systemic inflammatory response syndrome (SIRS) after cardiopulmonary bypass in children with congenital heart disease.

METHODS

A total of 90 children with congenital heart disease who underwent cardiopumonary bypass surgery between May 2012 and January 2016 were enrolled. According to the prsence or absence of SIRS after surgery, they were divided into SIRS group (n=43) and control group (n=47). Peripheral blood samples were collected before surgery, during surgery, and after surgery. Serum levels of IDO, C-reactive protein (CRP), and interleukin-6 (IL-6) were measured and compared between the two groups. The receiver operating characteristic (ROC) curve was used to evaluate their diagnostic efficiency.

RESULTS

Compared with the control group, the SIRS group had higher serum CRP levels at 72 hours after surgery, higher IL-6 levels during surgery and at 72 hours after surgery, and higher IDO levels at 24 and 72 hours after surgery. IDO had a certain value in the diagnosis of SIRS at 24 hours after surgery with an area under the ROC curve (AUC) of 0.793, a specificity of 100%, and a sensitivity of 58.14%. CRP, IL-6, and IDO had a certain value in the diagnosis of SIRS at 72 hours after surgery. IDO had the highest diagnostic efficiency with an AUC of 0.927, a specificity of 95.74%, and a sensitivity of 76.74% at 72 hours after surgery.

CONCLUSIONS

IL-6, CRP, and IDO have a certain value in the diagnosis of SIRS after surgery for congenital heart disease, and IDO has a higher diagnostic efficiency. IDO can predict the development of SIRS in children after surgery for congenital heart disease earlier.

Remote ischemic preconditioning attenuates cardiopulmonary bypass-induced lung injury

The use of cardiopulmonary bypass (CPB) in cardiac surgeries is known to induce pathological changes in vital organs such as lungs. Remote ischemic preconditioning (RIPC) is a protective strategy that has shown to be able to reduce tissue damage related to ischemia-reperfusion injury (IRI). The current study seeks to evaluate the beneficial effects of limb RIPC on lung tissues and function in a rat CPB model. RIPC, which consisted of three cycles of 5-min ischemia and subsequently 5-min reperfusion, was induced in the hind limbs of the animals via a tourniquet. Bronchoalveolar lavage (BAL) fluid analysis and hematoxylin and eosin staining revealed that limb RIPC could significantly attenuate CPB-induced pulmonary injury, as evidenced by a combination of lower total BAL protein content, less severe alveolar wall thickening and reduced intra-alveolar neutrophil infiltration. Consistently, RIPC was also found to improve the proliferation capacity of the bronchioalveolar stem cells isolated from the lung tissues in rats subjected to surgical procedure with CPB. These beneficial effects translated into significantly improved lung function. Further investigation suggested that RIPC could up-regulate the serum levels of several anti-inflammatory cytokines such as interleukin (IL)-4 and 10, which might play a role in its pulmonoprotective effects. Taken together, the current study provided convincing evidence that limb RIPC could be a useful strategy for minimizing CPB-induced organ injuries in patients undergoing CPB surgery.

Complement inhibition in biomaterial- and biosurface-induced thromboinflammation

Therapeutic medicine today includes a vast number of procedures involving the use of biomaterials, transplantation of therapeutic cells or cell clusters, as well as of solid organs. These treatment modalities are obviously of great benefit to the patient, but also present a great challenge to the innate immune system, since they involve direct exposure of non-biological materials, cells of non-hematological origin as well as endothelial cells, damaged by ischemia-perfusion in solid organs to proteins and cells in the blood. The result of such an exposure may be an inappropriate activation of the complement and contact/kallikrein systems, which produce mediators capable of triggering the platelets and PMNs and monocytes, which can ultimately result in thrombotic and inflammatory (i.e., a thrombo-inflammatory) response to the treatment modality. In this concept review, we give an overview of the mechanisms of recognition within the innate immunity system, with the aim to identify suitable points for intervention. Finally, we discuss emerging and promising techniques for surface modification of biomaterials and cells with specific inhibitors in order to diminish thromboinflammation and improve clinical outcome.