Daily Respiratory Research Analysis
Analyzed 75 papers and selected 3 impactful papers.
Summary
Three impactful respiratory studies emerged today: a meta-analysis of randomized trials shows inhaled nitric oxide provides no survival benefit in adult ARDS and may increase renal replacement therapy use; a multicenter COPD study maps distinct gut–lung microbiomes with airway modules linked to airflow limitation and treatment exposures; and an international registry analysis of prone positioning in COVID-19 ARDS identifies physiologic responses across consecutive cycles that correlate with ICU mortality.
Research Themes
- Critical appraisal of rescue therapies in ARDS
- Gut–lung axis and airway microbiome in COPD
- Physiologic response-guided use of prone positioning in ARDS
Selected Articles
1. Inhaled nitric oxide for acute respiratory distress syndrome in adults: a systematic review and meta-analysis.
Across 11 RCTs (n=1302), iNO did not reduce mortality in adult ARDS and may increase the need for renal replacement therapy, despite transient oxygenation gains. Only one trial had low risk of bias, underscoring the need for better-quality randomized evidence and refined patient selection.
Impact: This meta-analysis synthesizes randomized evidence to clarify the role of iNO in adult ARDS, directly informing clinical decision-making and stewardship of costly rescue therapies.
Clinical Implications: Avoid routine iNO use in adult ARDS; if used as rescue for refractory hypoxemia, monitor renal function closely and consider early de-escalation. Prioritize interventions with proven survival benefit and enroll patients in trials aimed at identifying responsive subgroups.
Key Findings
- Pooled mortality risk with iNO was not reduced (RR 1.07, 95% CI 0.93–1.23).
- iNO produced modest, short-term oxygenation improvements without patient-centered benefits.
- Signals of increased renal replacement therapy with iNO raise safety concerns.
Methodological Strengths
- Comprehensive multi-database search including trial registries with PROSPERO registration.
- Restriction to randomized controlled trials enhances internal validity.
Limitations
- Only one trial had low risk of bias; heterogeneity in dosing and co-interventions.
- Mortality follow-up timing and renal outcomes reporting varied across trials.
Future Directions: Identify ARDS phenotypes that might derive short-term physiologic or clinical benefit from iNO, standardize dosing/monitoring, and embed adaptive designs to test responsive subgroups.
BACKGROUND: Although inhaled nitric oxide (iNO) is used as a rescue therapy in patients with acute respiratory distress syndrome (ARDS), its impact on patient-centered outcomes remains uncertain. To address this gap, we conducted a systematic review of randomized controlled trials (RCTs) to test the hypothesis that the addition of iNO to standard care improves survival in adult patients with ARDS. METHODS: We searched PubMed, Embase, Cochrane Library, ClinicalTrials.gov, and WHO ICTRP for RCTs evaluating iNO in adult patients with ARDS through October 28, 2025. The primary outcome was mortality at the longest follow-up. Secondary outcomes included acute kidney injury (AKI), receipt of renal replacement therapy (RRT), duration of mechanical ventilation, length of intensive care unit stay, length of hospital stay, receipt of extracorporeal membrane oxygenation (ECMO), mean pulmonary artery pressure, partial pressure of arterial oxygen/fraction of inspiratory oxygen (PaO RESULTS: We included 11 RCTs comprising 1302 patients. Only one study was of low risk of bias. iNO therapy may result in no difference in mortality at the longest follow-up (relative risk [RR], 1.07; 95% confidence interval [CI], 0.93-1.23; I CONCLUSIONS: Although iNO may improve oxygenation slightly, it may not confer survival or other patient-centered benefits and may increase the need for RRT. High-quality randomized evidence is needed to guide the optimal patient selection for this therapeutic option. TRIAL REGISTRATION: PROSPERO (registration number: CRD42024573383).
2. Characterisation of the gut-lung axis microbiome in clinically stable patients with chronic obstructive pulmonary disease.
In a prospective multicenter study (60 COPD, 30 controls), airway and gut microbiomes were highly distinct, with only a small fraction of diversity associated with COPD. Oropharyngeal and sputum taxa associated with COPD were similar, whereas BALF differed, supporting OP swabs as a surrogate for sputum. Co-abundant bacterial modules in airway samples correlated with airflow limitation and clinical traits including exacerbation history and ICS use.
Impact: This study integrates multi-compartment microbiome profiling with network analysis, linking airway bacterial modules to clinically meaningful COPD features and suggesting a practical surrogate sampling strategy.
Clinical Implications: OP swabs can serve as a noninvasive surrogate for sputum microbiome profiling in COPD, enabling scalable monitoring. Airway bacterial modules associated with FEV1, exacerbations, and ICS use may inform phenotyping and microbiome-targeted interventions.
Key Findings
- Airway and stool microbiomes were highly dissimilar in both COPD and controls; only 0.37% of diversity was associated with COPD.
- COPD-associated taxa in oropharyngeal swabs mirrored sputum but differed from BALF, supporting OP swabs as a sputum surrogate.
- WGCNA identified co-abundant bacterial modules in OP swabs and sputum associated with airflow limitation (FEV1), exacerbation history, and ICS use.
Methodological Strengths
- Prospective, multicenter controlled design with matched multi-compartment sampling (OP, sputum, BALF, stool).
- Network-based (WGCNA) analysis linking microbial modules to clinical traits.
Limitations
- Modest sample size and potential low-biomass contamination bias in BALF.
- 16S rRNA sequencing limits taxonomic resolution and functional inference; associations are primarily cross-sectional.
Future Directions: Validate airway microbiome modules as biomarkers in larger longitudinal cohorts, integrate metagenomics/metabolomics to define function, and test microbiome-modifying interventions targeting COPD phenotypes.
BACKGROUND: Airway and gut dysbiosis have been reported in Chronic Obstructive Pulmonary Disease (COPD); however, their relationship and association with clinical features remain poorly understood. We aimed to characterise the lung and gut microbiome in patients with stable COPD and controls. METHODS: Prospective, multicentre, longitudinal and controlled study of n = 60 stable patients with COPD and n = 30 controls. In them, we analysed 16S rRNA-seq in oropharyngeal (OP) swabs, sputum, bronchoalveolar lavage fluid (BALF) and stool. Weighted gene co-expression network analysis (WGCNA) was employed in each sample type to identify modules of co-abundant bacteria associated with clinical traits. FINDINGS: We found that the microbiome in airway and stool samples was highly dissimilar both in patients and controls, with 0.37% of this diversity associated to COPD. The microbiome taxa associated with COPD in OP swabs and sputum were highly similar, but different from BALF, suggesting that OP swabs can be a surrogate sample of sputum. Finally, using WGCNA, we identified: (a) 5 modules in OP swabs and 3 in sputum associated with FEV INTERPRETATION: The gut and lung microbiomes in patients with COPD are distinct, but both clinically relevant as both present bacterial associations with airflow limitation, exacerbation history, and ICS use. FUNDING: ISC-III PI24/00476. FRPA.2014, ICREA-2024.
3. Time-dependent effects in consecutive cycles of prone positioning for acute respiratory failure: insights from the PROVENT-C19 Registry.
In 1523 COVID-19 ARF patients, survivors consistently exhibited greater PaO2/FiO2 improvements and smaller ventilatory ratio increases during and after prone cycles beyond the first. Total prone hours did not differ overall between survivors and non-survivors, and only the second cycle’s duration associated with mortality, suggesting physiologic response—rather than cumulative time—should guide ongoing prone use.
Impact: This large, international registry provides granular physiologic data across consecutive prone cycles, informing when continued prone positioning is likely to help—or not—in real-world ARDS care.
Clinical Implications: Use early physiologic response (oxygenation and ventilatory ratio) to decide on further prone cycles; consider diminishing returns beyond the second cycle and escalate care if oxygenation worsens after resupination.
Key Findings
- ICU survivors had higher Delta-PP and Delta-PostPP PaO2/FiO2 across analyzed prone cycles (p ≤ 0.001).
- Survivors had lower changes in ventilatory ratio during and after prone cycles (p < 0.05).
- Total prone time did not differ by outcome; only second-cycle duration associated with mortality (OR 0.986, 95% CI 0.978–0.994).
Methodological Strengths
- Large international registry (n=1523) with standardized physiologic endpoints across multiple cycles.
- Analysis of both oxygenation and ventilatory ratio changes during and after prone cycles.
Limitations
- Observational design with potential confounding and center-level practice variability.
- Limited generalizability beyond COVID-19 ARDS; prone duration and ventilator settings were not randomized.
Future Directions: Prospective trials to validate response-guided prone strategies and to determine optimal timing, duration, and criteria for cycle repetition or cessation.
BACKGROUND: Prone positioning is recommended for patients with acute respiratory distress syndrome not only to improve oxygenation, but also to reduce lung stress, and lower mortality. The association between improved oxygenation during prone position and reduced mortality is still controversial. In previous studies, oxygenation improvement during the first prone positioning cycle was linked to lower intensive care unit (ICU) mortality, especially with prolonged duration. However, physiological data during subsequent cycles were lacking. This study aims to explore the association between ICU mortality and physiological responses to prone positioning-such as arterial oxygenation, dead space, and respiratory mechanics-and to assess how the cumulative time spent in prone or supine positions across all studied cycles influences outcomes. METHODS: International registry including adult patients who underwent prone positioning for acute hypoxemic respiratory failure due to COVID-19. We measured the difference for arterial partial pressure of oxygen to inspired fraction of oxygen ratio (PaO2/FiO2) and ventilatory ratio between baseline supine position and at either the end of cycle of prone position (Delta-PP) or re-supination (Delta-PostPP), focusing on the cycles following the first one. RESULTS: We included 1523 patients from 53 centers. Both Delta-PP and Delta-PostPP for PaO2/FiO2 were significantly higher in ICU survivors than in ICU non-survivors for all the analyzed prone positioning cycles (p ≤ 0.001 for all comparisons). Delta-PP and Delta-PostPP for ventilatory ratio were significantly lower in ICU survivors than in ICU non-survivors for all the analyzed prone positioning cycles (p < 0.05 for all comparisons). No difference in the overall time spent in prone position was found between ICU survivors and non-survivors [61 (38, 84) h vs 58 (32, 85) h, respectively, p = 0.175]. The cumulative length of prone position was associated with ICU mortality only for the second prone positioning cycle [OR (95% CI) 0.986 (0.978, 0.994)]. No significant association was observed between the time spent in supine position and ICU mortality for all the analyzed prone positioning cycles. CONCLUSIONS: ICU survivors consistently demonstrated better oxygenation and more stable ventilatory ratio across studied prone positioning cycles, whereas non-survivors showed worsening oxygenation when returning supine and increased ventilatory ratio. Additionally, extending the duration of prone position beyond the second cycle may not significantly impact mortality.