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The clinical evolution of COVID-19 pneumonia is poorly understood. Identifying the metabolic pathways that are altered early with viral infection and their association with disease severity is crucial to understand COVID-19 pathophysiology, and guide clinical decisions. This study aimed at assessing the critical metabolic pathways altered with disease severity in hospitalized COVID-19 patients. Forty-nine hospitalized patients with COVID-19 pneumonia were enrolled in a prospective, observational, single-center study in Barcelona, Spain. Demographic, clinical, and analytical data at admission were registered. Plasma samples were collected within the first 48 h following hospitalization. Patients were stratified based on the severity of their evolution as moderate (N = 13), severe (N = 10), or critical (N = 26). A panel of 221 biomarkers was measured by targeted metabolomics in order to evaluate metabolic changes associated with subsequent disease severity. Our results show that obesity, respiratory rate, blood pressure, and oxygen saturation, as well as some analytical parameters and radiological findings, were all associated with disease severity. Additionally, ceramide metabolism, tryptophan degradation, and reductions in several metabolic reactions involving nicotinamide adenine nucleotide (NAD) at inclusion were significantly associated with respiratory severity and correlated with inflammation. In summary, assessment of the metabolomic profile of COVID-19 patients could assist in disease severity stratification and even in guiding clinical decisions.

WORD COUNT: 286 1 AbstractPurpose: Ventilator-induced diaphragm dysfunction or damage (VIDD) is highly prevalent in patients under mechanical ventilation (MV), but its analysis is limited by the difficulty of obtaining histological samples. In this study we compared diaphragm histological characteristics in Maastricht III (MSIII) and brain-dead (BD) organ donors and in control subjects undergoing thoracic surgery (CTL) after a period of either controlled or spontaneous MV (CMV or SMV).Methods: In this prospective study, biopsies were obtained from diaphragm and quadriceps.Demographic variables, comorbidities, severity on admission, treatment and ventilatory variables were evaluated. Immunohistochemical analysis (fiber size and type percentages) and quantification of abnormal fibers (a surrogate of muscle damage) were performed.Results: Muscle samples were obtained from 35 patients. MSIII (n=16) had more hours on MV (either CMV or SMV) than BD (n=14) and also spent more hours, and a greater percentage of time with diaphragm stimuli (time in assisted and spontaneous modalities). Cross sectional area (CSA) was significantly reduced in the diaphragm and quadriceps in both groups in comparison with CTL (n=5).Quadriceps CSA was significantly decreased in MSIII compared to BD but there were no differences in the diaphragm CSA between the two groups. Those MSIII who spent 100 or more hours without diaphragm stimuli presented reduced diaphragm CSA without changes in their quadriceps CSA.Proportion of internal nuclei in diaphragms of MSIII tended to be higher than BD, and their proportion of lipofuscin deposits tended to be lower, though there were no differences in the quadriceps fiber evaluation. Conclusions:This study provides the first evidence in humans about the effects of different modalities of MV (controlled, assisted and spontaneous) on diaphragm myofiber damage showing that diaphragm inactivity during mechanical ventilation is associated with the development of VIDD. KeywordsVentilator-induced Diaphragm Dysfunction or damage (VIDD), Atrophy, Mechanical Ventilation, Brain Death, Maastricht III, Muscle dysfunction.Most critically ill patients admitted to the Intensive Care Unit (ICU) require mechanical ventilation (MV) due to respiratory failure. MV may be associated with adverse effects on respiratory muscles, and disuse atrophy may be the most important mechanism in patients under controlled mechanical ventilation (CMV) [1]. During CMV, the electromyographic activity of the respiratory muscle fibers is diminished or may even stop [2], resulting in a rapid development of respiratory muscle dysfunction, especially diaphragm weakness. Ventilator-induced diaphragm dysfunction (VIDD) is defined as the loss of the diaphragm's capacity to generate force, together with muscle injury and fiber atrophy, and the same acronym has been used before to describe ventilator-induced diaphragm damage [3]. Both VIDD are associated particularly with the use of MV, typically after periods of CMV [4,5,6].VIDD may play a key role in th...