Anticoagulation for Extracorporeal Membrane Oxygenation: Between the Rock and the Hard Place

Investigation of heparin-loaded poly(ethylene glycol)-based hydrogels as anti-thrombogenic surface coatings for extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO), a critical life-sustaining tool, faces significant challenges for the maintenance of normal haemostasis due to the large volume of circulating blood continuously in contact with artificial surfaces, hyperoxia and excessive shear stresses of the extracorporeal circuit. From a biomaterials perspective, it has been hypothesised that drug eluting coatings composed of haemocompatible hydrogels loaded with an anticoagulant drug could potentially enhance the haemocompatibility of the circuit. Poly(ethylene glycol) (PEG) has been well established as a biocompatible and anti-fouling material with wide biomedical application. Unfractionated heparin is the most commonly used anticoagulant for ECMO. In the present study, the feasibility of using heparin-loaded PEG-based hydrogels as anti-thrombogenic surface coatings for ECMO was investigated. The hydrogels were synthesised by photopolymerisation using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinking monomer and poly(ethylene glycol) methacrylate (PEGMA) as the hydrophilic monomer, with heparin loaded into the pre-gel solution. Factors which could affect the release of heparin were investigated, including the ratio of PEGDA/PEGMA, water content, loading level of heparin and the flow of fluid past the hydrogel. Our results showed that increased crosslinker content and decreased water content led to slower heparin release. The hydrogels with water contents of 60 wt% and 70 wt% could achieve a sustained heparin release by adjusting the ratio of PEGDA/PEGMA. The anticoagulation efficacy of the released heparin was evaluated by measuring the activated clotting time of whole blood. The hydrogels with desirable heparin release profiles were prepared onto poly(4-methyl-1-pentene) (PMP) films with the same chemical composition as the PMP ECMO membranes. The coatings showed sustained heparin release with a cumulative release of 70-80% after 7 days. Haemocompatibility tests demonstrated that PEG hydrogel coatings significantly reduced platelet adhesion and prolonged plasma recalcification time. These results suggest that heparin-loaded PEG hydrogels are potential anti-thrombogenic coatings for ECMO.

Anti-thrombogenic Surface Coatings for Extracorporeal Membrane Oxygenation: A Narrative Review

Extracorporeal membrane oxygenation (ECMO) is used in critical care to manage patients with severe respiratory and cardiac failure. ECMO brings blood from a critically ill patient into contact with a non-endothelialized circuit which can cause clotting and bleeding simultaneously in this population. Continuous systemic anticoagulation is needed during ECMO. The membrane oxygenator, which is a critical component of the extracorporeal circuit, is prone to significant thrombus formation due to its large surface area and areas of low, turbulent, and stagnant flow. Various surface coatings, including but not limited to heparin, albumin, poly(ethylene glycol), phosphorylcholine, and poly(2-methoxyethyl acrylate), have been developed to reduce thrombus formation during ECMO. The present work provides an up-to-date overview of anti-thrombogenic surface coatings for ECMO, including both commercial coatings and those under development. The focus is placed on the coatings being developed for oxygenators. Overall, zwitterionic polymer coatings, nitric oxide (NO)-releasing coatings, and lubricant-infused coatings have attracted more attention than other coatings and showed some improvement in in vitro and in vivo anti-thrombogenic effects. However, most studies lacked standard hemocompatibility assessment and comparison studies with current clinically used coatings, either heparin coatings or nonheparin coatings. Moreover, this review identifies that further investigation on the thrombo-resistance, stability and durability of coatings under rated flow conditions and the effects of coatings on the function of oxygenators (pressure drop and gas transfer) are needed. Therefore, extensive further development is required before these new coatings can be used in the clinic.

Continuous renal replacement therapy in patients treated with extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a life‐saving therapy utilized for patients with severe life‐threatening cardiorespiratory failure. Patients treated with ECMO are among the most severely ill encountered in critical care and are at high‐risk of developing multiple organ dysfunction, including acute kidney injury (AKI) and fluid overload. Continuous renal replacement therapy (CRRT) is increasingly utilized inpatients on ECMO to manage AKI and treat fluid overload. The indications for renal replacement therapy for patients on ECMO are similar to those of other critically ill populations; however, there is wide practice variation in how renal supportive therapies are utilized during ECMO. For patients requiring both CRRT and ECMO, CRRT may be connected directly to the ECMO circuit, or CRRT and ECMO may be performed independently. This review will summarize current knowledge of the epidemiology of AKI, indications and timing of CRRT, delivery of CRRT, and the outcomes of patients requiring CRRT with ECMO.

Bedside veno-venous ECMO cannulation: A pertinent strategy during the COVID-19 pandemic

Background

Patient selection and cannulation arguably represent the key steps for the successful implementation of extracorporeal membrane oxygenation (ECMO) support. Cannulation is traditionally performed in the operating room or the catheterization laboratory for a number of reasons, including physician preference and access to real‐time imaging, with the goal of minimizing complications and ensuring appropriate cannula positioning. Nonetheless, the patients' critical and unstable conditions often require emergent initiation of ECMO and preclude the safe transport of the patient to a procedural suite.

Aims

Therefore, with the objective of avoiding delay with the initiation of therapy and reducing the hazard of transport, we implemented a protocol for bedside ECMO cannulation.

Matherial and Methods

A total of 89 patients required ECMO support at Hennepin County Medical Center between March 2015 and December 2019. Twenty‐eight (31%) required veno‐venous support and were all cannulated at the bedside. Overall survival was 71% with no morbidity or mortality related to the cannulation procedure.

Conclusion

In the current pandemic, the strategy of veno‐venous bedside cannulation may have additional benefits for the care of patients with refractory acute respiratory distress syndrome due to coronavirus disease‐2019, decreasing the risk of exposure of health care worker or other patients to the novel severe acute respiratory syndrome coronavirus‐2 occurring during patient transport, preparation, or during disinfection of the procedural suite and the transportation pathway after ECMO cannulation.