Evolution of membrane oxygenator technology for utilization during pediatric cardiopulmonary bypass

A new approach towards extracorporeal gas exchange and first in vitro results

OBJECTIVES

Extracorporeal life support (ECLS) pertains to therapeutic and prophylactic techniques utilized in a wide range of medical applications, with severe pulmonary diseases being the most prominent cases. Over the past decades, little progress has been made in advancing the basic principles and properties of gas exchangers. Here, in an unconventional approach, dialysis hollow fibers are handled with silicone to create a purely diffusive coating that prevents plasma leakage and promotes gas exchange.

METHODS

Commercial dialyzers of varying surface area and fiber diameter have been coated with silicone, to determine the impact of each parameter on performance. The impermeability of the silicone layer has been validated by pressurization and imaging methods. SEM images have revealed a homogeneous silicone film coating the lumen of the capillaries, while fluid dynamic investigations have confirmed its purely diffusive nature.

RESULTS

The hemodynamic behavior and the gas exchange efficiency of the silicone-coated prototypes have been investigated in vitro with porcine blood under various operating conditions. Their performance has been found to be similar to that of a commercial PMP oxygenator.

CONCLUSIONS

This novel class of gas exchangers is characterized by high versatility and expeditious manufacturing. Intraoperability between conventional ECLS systems and dialysis machines broadens the range of application infinitely. Ultimately, long-term clinical applicability ought to be determined over in vivo animal investigations.

Origins and Evolution of Extracorporeal Circulation: JACC Historical Breakthroughs in Perspective

Midway through the 20th century, direct open-heart operations were not yet a reality, awaiting safe methods to support the cardiopulmonary circulation during cardiac surgery. The scientific advancements collectively leading to safe cardiopulmonary bypass are considered some of the most impactful advances of modern medicine. Stimulated by the work of physiologists and engineers in the late 19th century, primitive pump and oxygenator designs were the forerunners of major work by DeBakey and others in roller pump design and by Gibbon in oxygenator development. Following Gibbon's historic successful closure of an atrial septal defect in 1953 with his heart-lung machine, it was left to Lillehei and Kirklin to first successfully repair large series of cardiac malformations. The history leading to these historic events and the subsequent evolution of cardiopulmonary bypass machines for short- and longer-term support is filled with engineering and surgical brilliance, daring innovations, and serendipity.

Evaluation of cytokine response to extracorporeal membrane oxygenation

RATIONALE

Increased cytokine response is common in patients receiving extracorporeal life support and is often a poor prognostic indicator. There is interest in using adjunctive cytokine adsorption technologies to reduce inflammatory burden, However, it is debated whether extracorporeal membrane oxygenation (ECMO) itself provides therapeutic benefit beyond gas exchange. Thus, we sought to characterize the inflammatory profile of ECMO in the first 72-96 h of and quantify its effect on cytokine levels in a case series of patients undergoing ECMO.

METHODS

Eight patients initiating ECMO were studied. Of these, we measured cytokines pre- and post-oxygenator over 96 h. Comparisons of cytokine levels were made across the oxygenator and over time.

RESULTS

The average age of patients was 64.3 years with 62% being male. Centrally cannulated patients had higher IL-6 levels (820.43 vs. 6907.53 pg/ml, p < 0.03), whereas peripherally cannulated patients had higher IL-12p70 levels (7.73 vs. 2.59 pg/ml, p < 0.05). Cytokine levels on day one included IL-12p70 (4.17 ± 2.56), IL-6 (4971.23 ± 8569.88), TNF (undetected), IL-8 (346.68 ± 670.18), IL-1B (undetected), and IL-10 (72.27 ± 87.9). Cytokine levels increased over 96 h; however, no significant differences were appreciated despite blood product transfusion. On day 3, IL-12p70 levels were significantly lower post-oxygenator (p < 0.05).

CONCLUSION

The inflammatory profile of ECMO does not change significantly over the early course of illness when accounting for transfusion. However, the decrease in IL-12p70 specifically at day 3 of ECMO may indicate adsorption of specific inflammatory markers by the oxygenator although the clinical significance of this is still unknown. Further investigation of the oxygenator on cytokine response is warranted.

Sorption/Diffusion Contributions to the Gas Permeation Properties of Bi-Soft Segment Polyurethane/Polycaprolactone Membranes for Membrane Blood Oxygenators

Due to their high hemocompatibility and gas permeation capacity, bi-soft segment polyurethane/polycaprolactone (PU/PCL) polymers are promising materials for use in membrane blood oxygenators. In this work, both nonporous symmetric and integral asymmetric PU/PCL membranes were synthesized, and the permeation properties of the atmospheric gases N₂, O₂, and CO₂ through these membranes were experimentally determined using a new custom-built gas permeation apparatus. Permeate pressure vs. time curves were obtained at 37.0 °C and gas feed pressures up to 5 bar. Fluxes, permeances, and permeability coefficients were determined from the steady-state part of the curves, and the diffusion and sorption coefficients were estimated from the analysis of the transient state using the time-lag method. Independent measurements of the sorption coefficients of the three gases were performed, under equilibrium conditions, in order to validate the new setup and procedure. This work shows that the gas sorption in the PU/PCL polymers is the dominant factor for the permeation properties of the atmospheric gases in these membranes.

Kappa opioid receptor agonists improve postoperative cognitive dysfunction in rats via the JAK2/STAT3 signaling pathway

Postoperative cognitive dysfunction (POCD) is a common and well‑known complication following surgery, particularly cardiopulmonary bypass (CPB) surgery. There are currently no suitable treatments for POCD, which is associated with increased illness and mortality rates. The present study aimed to identify a novel treatment for POCD. The protective effect of kappa opioid receptor (KOR) agonists on POCD in rats following CPB was determined and the regulatory mechanism of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway was examined. The rats were randomly divided into five groups: Sham operation (Sham group), CPB operation (CPB group), KOR agonist + CPB (K group), KOR agonist + norbinaltorphimine (nor‑BNI) + CPB (NK group), and KOR agonist + JAK2‑STAT3 specific pathway inhibitor + CPB (AG group). A water maze test and neurological function scores were used to evaluate POCD. Hematoxylin and eosin staining was used to observe hippocampal neurons. ELISA was used to detect the levels of inflammatory factors, oxidative stress factors and brain injury markers. Immunofluorescence was used to visualize the neurons. TUNEL staining and western blotting were used to detect neuronal apoptosis, and western blotting was also used to detect JAK2/STAT3 pathway‑related proteins. The KOR agonists significantly improved POCD. S‑100β and NSE detection revealed that KOR agonists alleviated brain damage in CPB rats, and this result was reversed by KOR antagonists. The KOR agonists led to a significantly reduced inflammatory response and oxidative stress, as determined by ELISA detection, and attenuated hippocampal neuronal apoptosis, as revealed by TUNEL staining and western blotting, compared with the results in the CPB group. Finally, the KOR agonists inhibited the expression levels of phosphorylated (p‑)JAK2 and p‑STAT3, rather than total JAK2 and STAT3, compared with levels in the CPB group. Taken together, KOR agonists improved POCD in rats with CPB by inhibiting the JAK2/STAT3 signaling pathway.

Drug Disposition and Pharmacotherapy in Neonatal ECMO: From Fragmented Data to Integrated Knowledge

Extracorporeal membrane oxygenation (ECMO) is a lifesaving support technology for potentially reversible neonatal cardiac and/or respiratory failure. As the survival and the overall outcome of patients rely on the treatment and reversal of the underlying disease, effective and preferentially evidence-based pharmacotherapy is crucial to target recovery. Currently limited data exist to support the clinicians in their every-day intensive care prescribing practice with the contemporary ECMO technology. Indeed, drug dosing to optimize pharmacotherapy during neonatal ECMO is a major challenge. The impact of the maturational changes of the organ function on both pharmacokinetics (PK) and pharmacodynamics (PD) has been widely established over the last decades. Next to the developmental pharmacology, additional non-maturational factors have been recognized as key-determinants of PK/PD variability. The dynamically changing state of critical illness during the ECMO course impairs the achievement of optimal drug exposure, as a result of single or multi-organ failure, capillary leak, altered protein binding, and sometimes a hyperdynamic state, with a variable effect on both the volume of distribution (Vd) and the clearance (Cl) of drugs. Extracorporeal membrane oxygenation introduces further PK/PD perturbation due to drug sequestration and hemodilution, thus increasing the Vd and clearance (sequestration). Drug disposition depends on the characteristics of the compounds (hydrophilic vs. lipophilic, protein binding), patients (age, comorbidities, surgery, co-medications, genetic variations), and circuits (roller vs. centrifugal-based systems; silicone vs. hollow-fiber oxygenators; renal replacement therapy). Based on the potential combination of the above-mentioned drug PK/PD determinants, an integrated approach in clinical drug prescription is pivotal to limit the risks of over- and under-dosing. The understanding of the dose-exposure-response relationship in critically-ill neonates on ECMO will enable the optimization of dosing strategies to ensure safety and efficacy for the individual patient. Next to in vitro and clinical PK data collection, physiologically-based pharmacokinetic modeling (PBPK) are emerging as alternative approaches to provide bedside dosing guidance. This article provides an overview of the available evidence in the field of neonatal pharmacology during ECMO. We will identify the main determinants of altered PK and PD, elaborate on evidence-based recommendations on pharmacotherapy and highlight areas for further research.