BACKGROUND: Optimal timing of mechanical ventilation in COVID-19 is uncertain. We sought to evaluate outcomes of delayed intubation and examine the ROX index (ie, [S pO 2 =F IO 2 ]/breathing frequency) to predict weaning from high-flow nasal cannula (HFNC) in patients with COVID-19. METHODS: We performed a multicenter, retrospective, observational cohort study of subjects with respiratory failure due to COVID-19 and managed with HFNC. The ROX index was applied to predict HFNC success. Subjects that failed HFNC were divided into early HFNC failure (^48 h of HFNC therapy prior to mechanical ventilation) and late failure (> 48 h). Standard statistical comparisons and regression analyses were used to compare overall hospital mortality and secondary end points, including time-specific mortality, need for extracorporeal membrane oxygenation, and ICU length of stay between early and late failure groups. RESULTS: 272 subjects with COVID-19 were managed with HFNC. One hundred sixty-four (60.3%) were successfully weaned from HFNC, and 111 (67.7%) of those weaned were managed solely in non-ICU settings. ROX index >3.0 at 2, 6, and 12 hours after initiation of HFNC was 85.3% sensitive for identifying subsequent HFNC success. One hundred eight subjects were intubated for failure of HFNC (61 early failures and 47 late failures). Mortality after HFNC failure was high (45.4%). There was no statistical difference in hospital mortality (39.3% vs 53.2%, P 5 .18) or any of the secondary end points between early and late HFNC failure groups. This remained true even when adjusted for covariates. CONCLUSIONS: In this retrospective review, HFNC was a viable strategy and mechanical ventilation was unecessary in the majority of subjects. In the minority that progressed to mechanical ventilation, duration of HFNC did not differentiate subjects with worse clinical outcomes. The ROX index was sensitive for the identification of subjects successfully weaned from HFNC. Prospective studies in COVID-19 are warranted to confirm these findings and to optimize patient selection for use of HFNC in this disease.

Purpose The outcomes of patients requiring invasive mechanical ventilation for COVID-19 remain poorly defined. We sought to determine clinical characteristics and outcomes of patients with COVID-19 managed with invasive mechanical ventilation in an appropriately resourced US health care system. Methods Outcomes of COVID-19 infected patients requiring mechanical ventilation treated within the Inova Health System between March 5, 2020 and April 26, 2020 were evaluated through an electronic medical record review. Results 1023 COVID-19 positive patients were admitted to the Inova Health System during the study period. Of these, 164 (16.0%) were managed with invasive mechanical ventilation. All patients were followed to definitive disposition. 70/164 patients (42.7%) had died and 94/164 (57.3%) were still alive. Deceased patients were older (median age of 66 vs. 55, p <0.0001) and had a higher initial d-dimer (2.22 vs. 1.31, p = 0.005) and peak ferritin levels (2998 vs. 2077, p = 0.016) compared to survivors. 84.3% of patients over 70 years old died in the hospital. Conversely, 67.4% of patients age 70 or younger survived to hospital discharge. Younger age, non-Caucasian race and treatment at a tertiary care center were all associated with survivor status. Conclusion Mortality of patients with COVID-19 requiring invasive mechanical ventilation is high, with particularly daunting mortality seen in patients of advanced age, even in a well-resourced health care system. A substantial proportion of patients requiring invasive mechanical ventilation were not of advanced age, and this group had a reasonable chance for recovery.

Purpose: The outcomes of patients requiring invasive mechanical ventilation for COVID-19 remain poorly defined. We sought to determine clinical characteristics and outcomes of patients with COVID-19 managed with invasive mechanical ventilation in an appropriately resourced US health care system. Methods: Outcomes of COVID-19 infected patients requiring mechanical ventilation treated within the Inova Health System between March 5, 2020 and April 26, 2020 were evaluated through an electronic medical record review. Results: 1023 COVID-19 positive patients were admitted to the Inova Health System during the study period. Of these, 165 (16.1%) were managed with invasive mechanical ventilation. At the time of data censoring, 63/165 patients (38.1%) had died and 102/165 (61.8%) were still alive. Of the surviving 102 patients, 17 (10.3%) remained on mechanical ventilation, 51 (30.9%) were extubated but remained hospitalized, and 34 (20.6%) had been discharged. Deceased patients were older (median age of 66 vs. 55, p <0.0001). 75.7% of patients over 70 years old had died at the time of data analysis. Conversely, 71.2% of patients age 70 or younger were still alive at the time of data analysis. Younger age, non-Caucasian race and treatment at a tertiary care center were all associated with survivor status. Conclusion: Mortality of patients with COVID-19 requiring invasive mechanical ventilation is high, with particularly daunting mortality seen in patients of advanced age, even in a well-resourced health care system. A substantial proportion of patients requiring invasive mechanical ventilation were not of advanced age, and this group had a reasonable chance for recovery.

INTRODUCTION Limited evidence exists regarding use of inhaled nitric oxide (iNO) in spontaneously breathing patients. We evaluated the effectiveness of continuous iNO via high-flow nasal cannula (HFNC) in COVID-19 respiratory failure. METHODS We performed a multicenter cohort study of patients with respiratory failure from COVID-19 managed with HFNC. Patients were stratified by administration of iNO via HFNC. Regression analysis was used to compare the need for mechanical ventilation and secondary endpoints including hospital mortality, length of stay, acute kidney injury, need for renal replacement therapy, and need for extracorporeal life support. RESULTS A total of 272 patients were identified and 66 (24.3%) of these patients received iNO via HFNC for a median of 88 h (interquartile range: 44, 135). After 12 h of iNO, supplemental oxygen requirement was unchanged or increased in 52.7% of patients. Twenty-nine (43.9%) patients treated with iNO compared to 79 (38.3%) patients without iNO therapy required endotracheal intubation ( P = .47). After multivariable adjustment, there was no difference in need for mechanical ventilation between groups (odds ratio: 1.53; 95% confidence interval [CI]: 0.74-3.17), however, iNO administration was associated with longer hospital length of stay (incidence rate ratio: 1.41; 95% CI: 1.31-1.51). No difference was found for mortality, acute kidney injury, need for renal replacement therapy, or need for extracorporeal life support. CONCLUSION In patients with COVID-19 respiratory failure, iNO delivered via HFNC did not reduce oxygen requirements in the majority of patients or improve clinical outcomes. Given the observed association with increased length of stay, judicious selection of those likely to benefit from this therapy is warranted.

Background Childhood acute lymphoblastic leukemia (ALL) has a very high cure rate, however, long-term survivors are at increased risk of chronic medical illnesses that are likely in part microbiome mediated. Previous studies comparing microbiota of pediatric ALL survivors to healthy siblings showed altered composition in survivors. Longitudinal microbiome changes through treatment leading to these alterations are unknown. Methods Children with ALL were enrolled and stool samples were collected at diagnosis and at the end of induction, consolidation, interim maintenance I, delayed intensification, interim maintenance II, as well as approximately 3 months and 6 months into maintenance. Stool samples from healthy siblings were used as controls. Clinical data were collected. DNA was extracted from stool samples and 16S rRNA was sequenced for analysis of hypervariable region V4. Differences in alpha and beta diversities and relative abundance of taxa were calculated between phases and with sibling controls. Results 35 ALL patients age 3 months-19 years were included. The diagnoses were 14 standard risk pre-B ALL, 14 high risk pre-B ALL, 6 T-ALL, and 1 relapsed pre-B ALL. Stool samples were sequenced from 19 healthy siblings. Statistically significant differences in alpha diversity (Shannon) were found between healthy siblings and ALL patients during the more intense chemotherapy phases before low dose maintenance (Figure 1A). Beta diversity (Bray-Curtis), was significantly different between microbiota of ALL patients at diagnosis and their siblings, as well as between ALL patients at diagnosis and at each of the subsequent treatment phases (Figure 1B). Longitudinal comparison using multivariate analysis showed that leukemia risk group (high risk vs standard risk) and antibiotic treatment were significant factors in beta diversity changes. The relative abundance of microbes showed that with treatment, ALL patients exhibit a significant decrease in the phylum Verrucomicrobiota, driven by the genus Akkermansia, which is beneficial to health and is associated with protection against obesity and other chronic inflammatory diseases (Figure 2). Proteobacteria and Fusobacteria, which include proinflammatory species, were increased. Conclusion Pediatric ALL patients have decreased diversity of gut microbes at diagnosis and during treatment. The types of gut microbes harbored in ALL patients are already different than their siblings at diagnosis and continue to change during treatment, but may begin to recover in low dose maintenance therapy. Taxa considered to be beneficial are depleted, while more pathogenic microbes become prominent. Microbiota changes are likely influenced by intensity of chemotherapy and antibiotic exposure. Continued longitudinal follow up is needed to determine whether these changes correlate with adverse long term health outcomes. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

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Background Clostridioides difficile infection (CDI) is frequent in pediatric patients with acute lymphoblastic leukemia (ALL). Studies have shown upwards of 20% positivity rate in CDI testing among pediatric oncology patients, and up to several percent in pediatric ALL patients in the first 180 days of diagnosis. Antibiotic usage has been variably linked to CDI positivity in these populations. As CDI testing is usually done in symptomatic patients, the question of C. difficile carriage versus CDI has not been addressed. We and others have shown that microbiome is altered in pediatric ALL patients and survivors. We conducted a longitudinal stool microbiome study in pediatric ALL patients and tested the hypothesis that alteration of the microbiome during ALL treatment promotes C. difficile carriage. Methods Children with ALL were prospectively recruited on a rolling basis and stool samples were collected at diagnosis (Dx) and at the end of induction (EOI), consolidation (EOC), interim maintenance I (IMI), delayed intensification (DI), interim maintenance II (IMII), as well as approximately 3 months and 6 months into maintenance (M3, M6). Stool samples from healthy siblings were used as controls. TaqMan-based quantitative-PCR (qPCR) was performed on DNA extracted from stool samples to detect C. diff 16S rRNA, tcdA, (Toxin A) and tcdB (Toxin B) genes . Samples positive or either tcdA or tcdB, or both, were designated positive for toxigenic C. difficile. 16S rRNA hypervariable region V4 was sequenced and analyzed for microbiome diversity and relative abundance of microbiota. Results 32 ALL patients age 3 months-19 years were included. The diagnoses were 12 standard risk and 14 high risk pre-B ALL, 5 T-ALL, and 1 relapsed pre-B ALL. Stool samples were collected from 18 healthy siblings. The numbers of samples tested at each treatment phase were: 29 Dx, 24 EOI, 23 EOC, 25 IMI, 21 DI, 6 IMII, 14 M3, 7 M6. No patient had symptoms suggestive of CDI, and no patient was clinically tested or treated for CDI. Total number of stool samples tested was 149, of which 43 (29%) were positive for toxigenic C. difficile (Figure 1). At diagnosis, 2/29 (7%) patients were positive, compared to 2/18 (11%) in healthy siblings. At EOI, positivity rate increased to 17%, then up to 40% - 52% at EOC, IMI, and DI. C. difficile positivity were lower around 30% at M3 and M6, although few patients reached maintenance to contribute samples for analysis. Twenty-five patients (78%) were positive at some phase. Longitudinal analysis of individual patients showed that C. difficile positivity was intermittent through treatment phases; only 3 patients remained persistently positive. Seven patients (22%) were never positive. Multivariate analysis showed that EOC, IMI, and DI treatment phases were significant risk factors for C. difficile carriage. Neither the number of antibiotics nor the number of antibiotic courses administered was significant. Leukemia risk stratification (high risk versus standard risk) also did not correlate with C. difficile positivity. Microbiome analysis showed statistically significant differences in relative abundance of certain taxa between C. diff positive and negative samples at the class, order, and family levels (Figure 2). Examples include depletion of the class Verrucomicrobiae, which contains protective Akkermansia, and depletion of the common taxa Bifidobacteriaceae and Ruminococcaceae. Conclusion Longitudinal PCR testing of toxigenic C. difficile in pediatric ALL patients demonstrated increased C. difficile prevalence further into treatment phases. C. difficile carriage correlated significantly with depletion of several bacterial taxa, as microbiome diversity decreased overall with successive treatment phases. Our data lend support to the hypothesis that altered microbiome in ALL treatment allows permissibility for C. difficile carriage. In addition, no C. difficile positive patient had symptoms of CDI, therefore, caution must be taken in clinical testing, as there is a high asymptomatic carriage rate. Further longitudinal testing during maintenance and off-therapy is needed to see if C. difficile carriage rate returns to baseline and correlates with recovery of gut microbiome. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.