Cardiac Support: Emphasis on Venoarterial ECMO

Bacterial lipopolysaccharide-induced endothelial activation and dysfunction: a new predictive and therapeutic paradigm for sepsis

BACKGROUND

Lipopolysaccharide, a highly potent endotoxin responsible for severe sepsis, is the major constituent of the outer membrane of gram-negative bacteria. Endothelial cells participate in both innate and adaptive immune responses as the first cell types to detect lipopolysaccharide or other foreign debris in the bloodstream. Endothelial cells are able to recognize the presence of LPS and recruit specific adaptor proteins to the membrane domains of TLR4, thereby initiating an intracellular signaling cascade. However, lipopolysaccharide binding to endothelial cells induces endothelial activation and even damage, manifested by the expression of proinflammatory cytokines and adhesion molecules that lead to sepsis.

MAIN FINDINGS

LPS is involved in both local and systemic inflammation, activating both innate and adaptive immunity. Translocation of lipopolysaccharide into the circulation causes endotoxemia. Endothelial dysfunction, including exaggerated inflammation, coagulopathy and vascular leakage, may play a central role in the dysregulated host response and pathogenesis of sepsis. By discussing the many strategies used to treat sepsis, this review attempts to provide an overview of how lipopolysaccharide induces the ever more complex syndrome of sepsis and the potential for the development of novel sepsis therapeutics.

CONCLUSIONS

To reduce patient morbidity and mortality, preservation of endothelial function would be central to the management of sepsis.

A numerical study of the hemodynamic behavior and gas transport in cardiovascular systems with severe cardiac or cardiopulmonary failure supported by venoarterial extracorporeal membrane oxygenation

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) has been extensively demonstrated as an effective means of bridge-to-destination in the treatment of patients with severe ventricular failure or cardiopulmonary failure. However, appropriate selection of candidates and management of patients during Extracorporeal membrane oxygenation (ECMO) support remain challenging in clinical practice, due partly to insufficient understanding of the complex influences of extracorporeal membrane oxygenation support on the native cardiovascular system. In addition, questions remain as to how central and peripheral venoarterial extracorporeal membrane oxygenation modalities differ with respect to their hemodynamic impact and effectiveness of compensatory oxygen supply to end-organs. In this work, we developed a computational model to quantitatively address the hemodynamic interaction between the extracorporeal membrane oxygenation and cardiovascular systems and associated gas transport. Model-based numerical simulations were performed for cardiovascular systems with severe cardiac or cardiopulmonary failure and supported by central or peripheral venoarterial extracorporeal membrane oxygenation. Obtained results revealed that: 1) central and peripheral venoarterial extracorporeal membrane oxygenation modalities had a comparable capacity for elevating arterial blood pressure and delivering oxygenated blood to important organs/tissues, but induced differential changes of blood flow waveforms in some arteries; 2) increasing the rotation speed of extracorporeal membrane oxygenation pump (ω) could effectively improve arterial blood oxygenation, with the efficiency being especially high when ω was low and cardiopulmonary failure was severe; 3) blood oxygen indices (i.e., oxygen saturation and partial pressure) monitored at the right radial artery could be taken as surrogates for diagnosing potential hypoxemia in other arteries irrespective of the modality of extracorporeal membrane oxygenation; and 4) Left ventricular (LV) overloading could occur when ω was high, but the threshold of ω for inducing clinically significant left ventricular overloading depended strongly on the residual cardiac function. In summary, the study demonstrated the differential hemodynamic influences while comparable oxygen delivery performance of the central and peripheral venoarterial extracorporeal membrane oxygenation modalities in the management of patients with severe cardiac or cardiopulmonary failure and elucidated how the status of arterial blood oxygenation and severity of left ventricular overloading change in response to variations in ω. These model-based findings may serve as theoretical references for guiding the application of venoarterial extracorporeal membrane oxygenation or interpreting in vivo measurements in clinical practice.

Postcardiotomy Venoarterial Extracorporeal Membrane Oxygenation With and Without Intra-Aortic Balloon Pump

OBJECTIVES

To compare the outcomes of patients with postcardiotomy shock treated with venoarterial extracorporeal membrane oxygenation (VA-ECMO) only compared with VA-ECMO and intra-aortic balloon pump (IABP).

DESIGN

A retrospective multicenter registry study.

SETTING

At 19 cardiac surgery units.

PARTICIPANTS

A total of 615 adult patients who required VA-ECMO from 2010 to 2018. The patients were divided into 2 groups depending on whether they received VA-ECMO only (ECMO only group) or VA-ECMO plus IABP (ECMO-IABP group).

MEASUREMENTS AND MAIN RESULTS

The overall series mean age was 63 ± 13 years, and 33% were female. The ECMO-only group included 499 patients, and 116 patients were in the ECMO-IABP group. Urgent and/or emergent procedures were more common in the ECMO-only group. Central cannulation was performed in 47% (n = 54) in the ECMO-IABP group compared to 27% (n = 132) in the ECMO-only group. In the ECMO-IABP group, 58% (n = 67) were successfully weaned from ECMO, compared to 46% (n = 231) in the ECMO-only group (p = 0.026). However, in-hospital mortality was 63% in the ECMO-IABP group compared to 65% in the ECMO-only group (p = 0.66). Among 114 propensity score-matched pairs, ECMO-IABP group had comparable weaning rates (57% v 53%, p = 0.51) and in-hospital mortality (64% v 58%, p = 0.78).

CONCLUSIONS

This multicenter study showed that adjunctive IABP did not translate into better outcomes in patients treated with VA-ECMO for postcardiotomy shock.

Rewarming from accidental hypothermia enhances whole blood clotting properties in a murine model

BACKGROUND

Hypothermia triggers coagulation, which can lead to the development of a life-threatening condition. We previously reported that hypothermia induces platelet activation in the spleen, resulting in microthrombosis after rewarming. However, the changes in whole blood clotting properties that occur remain unclear. Using thromboelastography, we investigated blood clotting activity and the effects of rewarming in a murine model of hypothermia.

METHODS

C57Bl/6 mice were exposed to an ambient temperature of -20 °C under general anesthesia until their rectal temperature decreased to 15 °C. One group of mice was kept at 4 °C for 2 h and then euthanized. Another group was rewarmed, kept in normal conditions for 24 h, and then euthanized. Tissue and citrated whole blood samples were obtained from the mice for histopathological analysis, flow cytometry, and thromboelastography.

RESULTS

Hypothermia induced the activation of platelets in the spleen; however, rewarming significantly reduced the number of activated platelets in the spleen while their numbers significantly increased in peripheral blood. In hypothermic mice not subjected to rewarming, no increase in activated platelets was observed in peripheral blood. Thromboelastography analysis showed that whole blood samples from the rewarmed mice displayed an enhanced clotting strength.

CONCLUSIONS

Rewarming from hypothermia enhances whole blood coagulation activity accompanied by an increase in the number of active platelets in peripheral blood. This phenomenon may lead to formation of microthrombi and thrombotic disorders.

Advanced heart failure with reduced ejection fraction

Patients suffering advanced heart failure with reduced ejection fraction (HFrEF) account for a large portion of patients admitted to hospitals worldwide. Mortality and 30-day readmission rates for HFrEF are now a focus of value-based payment models, making management of this disease a priority for hospitals, physicians, and payers alike. Angiotensin-converting enzyme inhibitors have been the cornerstone of therapy for decades. However, with treatment, the prognosis for patients with advanced HFrEF remains poor. Fortunately, advances in medical therapy and mechanical support offer some patients improvement in both survival and quality of life. We review advances in short- and long-term mechanical support and explore changes to organ allocation for cardiac transplantation. In addition, we provide a guide to facilitate appropriate referral to an advanced heart failure team.

Awake veno-arterial extracorporeal membrane oxygenation in patients with perioperative period acute heart failure in cardiac surgery

Background

Extracorporeal membrane oxygenation (ECMO) is an effective extracorporeal life support technology that has been applied to treat cardiorespiratory failure patients. Some medical centers have started using ECMO on awake, non-intubated, spontaneously breathing patients, as this strategy offers several benefits over mechanical ventilation. However, most awake-ECMO methods focus on venovenous ECMO, and few cases of awake veno-arterial ECMO (V-A ECMO) have been reported, especially in perioperative acute heart failure. Therefore, our study aimed to examine awake—V-A ECMO cases that were not given continuous sedation or invasive mechanical ventilation (IMV) during perioperative heart failure.

Method

In total, 40 ECMO patients from December 2013 to November 2019 were divided into 2 groups (the awake-ECMO group and the asleep-ECMO group) according to the ventilation use. The demographics, patient outcomes, and ECMO parameters were collected and retrospectively analyzed.

Results

We identified 12 cases of awake ECMO without continuous ventilation, and 28 cases of simultaneous IMV and ECMO (asleep ECMO). Awake-ECMO patients showed fewer complications and better outcomes compared to ventilation patients. All patients in the awake group were successfully weaned off ECMO, while only 5 (18%) patients were weaned off ECMO in the asleep group. Furthermore, 9 (75%) patients survived until discharge in the awake group vs. 3 (11%) in the asleep group; 3 patients died of septic shock after weaning in the awake group, while 25 patients died of septic shock, hemodynamic disorder, bleeding, cerebral hemorrhage, etc., in the asleep group. These complications, including bleeding, pneumonia, hemolysis, and abdominal distension, etc., occurred less frequently in the asleep group compared to the awake group (P<0.05).

Conclusions

Awake V-A ECMO is an effective, feasible, and safe strategy in patients with perioperatively acute heart failure and can be applied as a bridge to cardiac function recovery or transplantation.

Extracorporeal Membrane Oxygenation in Transport Part 2: Complications and Troubleshooting

Factors taken for granted while the extracorporeal membrane oxygenation (ECMO) patient is maintained in a hospital setting can become critical when planning for transport. These issues include but are not limited to positioning of patients on a small transport stretcher, positioning of cannulas and equipment, ensuring adequate power sources and supply, inefficient temperature control, and a much higher risk of decannulation. It is paramount to be comfortable with the management strategies required to handle common complications of ECMO with limited resources in a relatively austere environment. Coagulopathy and bleeding are the most common complications occurring in up to 50% of ECMO patients. Loss of flow and hypotension from loss of volume or profound vasodilation after ECMO initiation need to be managed accordingly. Oxygenator malfunction can occur, and clinicians must be able to recognize the indicators of this complication promptly. Loss of pulsatility, low end-tidal carbon dioxide (ETCO₂), and differential hypoxia are common complications in venoarterial ECMO. In addition, an air embolism is life-threatening on venoarterial ECMO but may be better tolerated in the setting of venovenous ECMO. Recirculation in venovenous ECMO leads to circulation of poorly oxygenated blood and must be recognized and addressed. Lastly, pump failure, circuit rupture, and decannulation are devastating complications. Over the last decade, the use of extracorporeal membrane oxygenation (ECMO) has accelerated rapidly,^1-3 providing support for patients in severe respiratory or cardiac failure. With ongoing clinical experience and improvements in technology, the indications for ECMO are increasing.⁴ Many areas are developing centralized ECMO centers to serve their surrounding communities.^5-7 To use a centralized ECMO referral model, patients need access to effective, safe critical care transport, but transporting a patient on ECMO carries a significant risk of adverse events.^8-13 The purpose of this review is to highlight some of the most common adverse events in ECMO transports and provide management suggestions. Note that these recommendations are not a substitution for close collaboration with medical control, and all adverse events should be promptly reported per organizational protocols.

The use of ECMO in ICU. Recommendations of the Spanish Society of Critical Care Medicine and Coronary Units

The use of extracorporeal membrane oxygenation systems has increased significantly in recent years; given this reality, the Spanish Society of Critical Intensive Care Medicine and Coronary Units (SEMICYUC) has decided to draw up a series of recommendations that serve as a framework for the use of this technique in intensive care units. The three most frequent areas of extracorporeal membrane oxygenation systems use in our setting are: as a cardiocirculatory support, as a respiratory support and for the maintenance of the abdominal organs in donors. The SEMICYUC appointed a series of experts belonging to the three working groups involved (Cardiological Intensive Care and CPR, Acute Respiratory Failure and Transplant work group) that, after reviewing the existing literature until March 2018, developed a series of recommendations. These recommendations were posted on the SEMICYUC website to receive suggestions from the intensivists and finally approved by the Scientific Committee of the Society. The recommendations, based on current knowledge, are about which patients may be candidates for the technique, when to start it and the necessary infrastructure conditions of the hospital centers or, the conditions for transfer to centers with experience. Although from a physiopathological point of view, there are clear arguments for the use of extracorporeal membrane oxygenation systems, the current scientific evidence is weak, so studies are needed that define more precisely which patients benefit most from the technique and when they should start.

Venoarterial Extracorporeal Membrane Oxygenation Increased Immune Function of Spleen and Decreased Reactive Oxygen Species During Post-Resuscitation

We aimed to investigate the effect of venoarterial extracorporeal membrane oxygenation (VA-ECMO) on immune function of the spleen and reactive oxygen species (ROS) during post-resuscitation in a porcine model. After 8 min of untreated ventricular fibrillation and 6 min of basic life support, pigs were randomized into two groups: Group 1 received VA-ECMO and Group 2 received conventional cardiopulmonary resuscitation. After successful return of spontaneous circulation, the hemodynamic status was determined and blood samples were collected at 0, 1, 2, 4, and 6 h. Surviving pigs were euthanized 6 h after return of spontaneous circulation, their spleens were harvested and the T-cells were separated. Then, we investigated immune function parameters of the spleen and ROS levels. VA-ECMO increased the return of spontaneous circulation and 6 h survival rate after return of spontaneous circulation. Compared with the conventional cardiopulmonary resuscitation group, the VA-ECMO group showed increased superoxide dismutase and decreased malondialdehyde and ROS levels. Furthermore, VA-ECMO was associated with a high rate of CD4+ and CD4+/CD8+, high levels of interleukin 2, interferon γ, and interferon γ/interleukin 4, as well as high proliferation of lymphocytes. The apoptotic rate of T-cells was lower in the VA-ECMO group than it was in the conventional cardiopulmonary resuscitation group. VA-ECMO increased immune function of spleen and decreased ROS levels during post-resuscitation. Further research is expected to illustrate whether the differences in immune responses are due to ROS or some other perfusion related effect on spleen.

Cerebral Pathophysiology in Extracorporeal Membrane Oxygenation: Pitfalls in Daily Clinical Management

Extracorporeal membrane oxygenation (ECMO) is a life-saving technique that is widely being used in centers throughout the world. However, there is a paucity of literature surrounding the mechanisms affecting cerebral physiology while on ECMO. Studies have shown alterations in cerebral blood flow characteristics and subsequently autoregulation. Furthermore, the mechanical aspects of the ECMO circuit itself may affect cerebral circulation. The nature of these physiological/pathophysiological changes can lead to profound neurological complications. This review aims at describing the changes to normal cerebral autoregulation during ECMO, illustrating the various neuromonitoring tools available to assess markers of cerebral autoregulation, and finally discussing potential neurological complications that are associated with ECMO.