Vitamin D status and supplementation in adult patients receiving extracorporeal membrane oxygenation

Nutrition during extracorporeal life support: A review of pathophysiological bases and application of guidelines

BACKGROUND

Patients on extracorporeal life support (ECLS), either for respiratory or cardiac support, are at high risk of malnutrition; guidelines on nutrition in critical care have not incorporated solid evidence regarding these settings. The aim of this narrative review is to gather the available evidence in the existing literature and transpose general principles to the ECLS population.

METHODS

A literature review of observational and interventional studies on nutrition during ECLS, and evaluation of nutrition guidelines in this perspective.

RESULTS

Nutrition is paramount for improving outcomes in ECLS, as well as in critically ill patients. The caloric needs during ECLS can vary according to the severity of the clinical state, sedation, paralysis, and temperature stability. Precise evaluation of energy expenditure by indirect calorimetry is difficult because ECLS is a system dedicated to removing carbon dioxide; however, modified equations composed of carbon dioxide values taken from the membrane lung are available. Guidelines suggest starting early enteral nutrition (EN) with a hypocaloric (70%-80% of the needs) strategy, also in acute states such as septic or cardiogenic shock. Moreover, EN, despite previous concerns, is feasible in prone position, an increasingly adopted strategy during mechanical ventilation. The catabolic state is maximal in these patients, causing a protein and muscular reduction. Therefore, adequate protein delivery should be guaranteed by administering a high protein intake of up to 2 g/kg/day.

CONCLUSIONS

Studies on nutrition tailored to ECLS patients are warranted. Early hypocaloric EN with high protein intake, tailored on indirect calorimetry, may be the most appropriate option.

Preventing the development of severe COVID-19 by modifying immunothrombosis

BACKGROUND

COVID-19-associated acute respiratory distress syndrome (ARDS) is associated with significant morbidity and high levels of mortality. This paper describes the processes involved in the pathophysiology of COVID-19 from the initial infection and subsequent destruction of type II alveolar epithelial cells by SARS-CoV-2 and culminating in the development of ARDS.

MAIN BODY

The activation of alveolar cells and alveolar macrophages leads to the release of large quantities of proinflammatory cytokines and chemokines and their translocation into the pulmonary vasculature. The presence of these inflammatory mediators in the vascular compartment leads to the activation of vascular endothelial cells platelets and neutrophils and the subsequent formation of platelet neutrophil complexes. These complexes in concert with activated endothelial cells interact to create a state of immunothrombosis. The consequence of immunothrombosis include hypercoagulation, accelerating inflammation, fibrin deposition, migration of neutrophil extracellular traps (NETs) producing neutrophils into the alveolar apace, activation of the NLRP3 inflammazome, increased alveolar macrophage destruction and massive tissue damage by pyroptosis and necroptosis Therapeutic combinations aimed at ameliorating immunothrombosis and preventing the development of severe COVID-19 are discussed in detail.

The pathophysiology of SARS-CoV-2: A suggested model and therapeutic approach

In this paper, a model is proposed of the pathophysiological processes of COVID-19 starting from the infection of human type II alveolar epithelial cells (pneumocytes) by SARS-CoV-2 and culminating in the development of ARDS. The innate immune response to infection of type II alveolar epithelial cells leads both to their death by apoptosis and pyroptosis and to alveolar macrophage activation. Activated macrophages secrete proinflammatory cytokines and chemokines and tend to polarise into the inflammatory M1 phenotype. These changes are associated with activation of vascular endothelial cells and thence the recruitment of highly toxic neutrophils and inflammatory activated platelets into the alveolar space. Activated vascular endothelial cells become a source of proinflammatory cytokines and reactive oxygen species (ROS) and contribute to the development of coagulopathy, systemic sepsis, a cytokine storm and ARDS. Pulmonary activated platelets are also an important source of proinflammatory cytokines and ROS, as well as exacerbating pulmonary neutrophil-mediated inflammatory responses and contributing to systemic sepsis by binding to neutrophils to form platelet-neutrophil complexes (PNCs). PNC formation increases neutrophil recruitment, activation priming and extraversion of these immune cells into inflamed pulmonary tissue, thereby contributing to ARDS. Sequestered PNCs cause the development of a procoagulant and proinflammatory environment. The contribution to ARDS of increased extracellular histone levels, circulating mitochondrial DNA, the chromatin protein HMGB1, decreased neutrophil apoptosis, impaired macrophage efferocytosis, the cytokine storm, the toll-like receptor radical cycle, pyroptosis, necroinflammation, lymphopenia and a high Th17 to regulatory T lymphocyte ratio are detailed.