Inhaled nitric oxide (NO), a selective pulmonary vasodilator, gained FDA approval in 1999 for neonatal use, specifically for newborns with hypoxemic respiratory failure and persistent pulmonary hypertension. Over time, its application expanded to critically ill adult patients facing hypoxemic respiratory failure and postoperative cardiac patients.
Inhaled NO’s therapeutic benefits are attributed to its ability to reduce intrapulmonary shunting, leading to improved oxygenation in mechanically-ventilated adults with severe acute respiratory distress syndrome (ARDS) during the initial 24 hours of inhalation. However, prior randomized trials demonstrated limited efficacy when inhaled NO was restricted to 20 ppm for adults with ARDS.
Meanwhile, in vitro studies have highlighted the bactericidal properties of nitric oxide in solution and its potential to inhibit viral replication. Previous research primarily employed low-dose inhaled NO to facilitate pulmonary vasodilation and enhance oxygenation. However, the optimal antiviral dose of inhaled NO remained undefined.
Recent studies have explored the use of high-dose inhaled nitric oxide, reaching up to 300 ppm, demonstrating sustainable improvements in systemic oxygenation in non-intubated hospitalized adults and reduced hospitalization lengths in pregnant and pediatric patients with viral and bacterial pneumonia.
Yet, the potential of high-antiviral doses of inhaled NO to enhance systemic oxygenation in critically ill COVID-19 patients requiring mechanical ventilation remained unexplored.
In response to mounting evidence, this study aimed to investigate whether high-dose inhaled NO administered early after COVID-19 infection onset could be beneficial for critically ill patients with acute hypoxemic respiratory failure. This phase II, multicenter, single-blind, randomized (1:1), controlled, parallel-arm trial focused on evaluating the impact of inhaled NO on systemic oxygenation after 48 hours among mechanically ventilated COVID-19 patients.
Methods
Patient Selection: Critically ill patients with confirmed COVID-19, requiring mechanical ventilation and experiencing acute hypoxemic respiratory failure, were eligible for the study, following predefined criteria related to age, comorbidities, and respiratory status.
Randomization: Eligible patients were randomly assigned to either receive high-dose inhaled NO or a placebo in a 1:1 ratio.
Intervention: The experimental group received high-antiviral doses of inhaled NO, carefully monitored for dosage control. The control group received a placebo mimicking the inhalation process, resulting in a single-blind study design.
Monitoring: Close monitoring of key parameters, including systemic oxygenation, respiratory mechanics, and relevant clinical markers, was maintained over a 48-hour period.
Data Collection: Extensive data on patient demographics, baseline characteristics, and clinical outcomes were meticulously collected and analyzed.
Results
The study’s findings revealed that high-dose inhaled NO improved systemic oxygenation in mechanically ventilated, critically ill patients suffering from acute hypoxemic respiratory failure due to COVID-19 pneumonia. The median PaO2/FiO2 ratio increased from 177 (125, 241) mm Hg to 200 (157, 239) mm Hg in the treatment group but decreased from 195 (120, 235) mm Hg to 183 (122, 235) mm Hg in the control group.
A larger proportion of patients in the inhaled NO group achieved PaO2/FiO2 >300 mmHg for at least 24 hours at 28 days compared to the usual care group. However, the time required to reach this level of oxygenation was similar. There were no significant differences in mortality or other exploratory clinical outcomes, but participants receiving inhaled NO reported fewer sensory symptoms at 90 days post-randomization.
Discussion
This investigator-initiated trial, characterized by its phase II, multicenter, single-blind, randomized, controlled, parallel-arm design, demonstrated the effectiveness of high-dose inhaled NO in improving systemic oxygenation in critically ill COVID-19 patients with acute hypoxemic respiratory failure. Although mortality rates and other clinical outcomes remained comparable between the treatment and control groups, the reduction in sensory symptoms among those receiving inhaled NO merits attention.
Furthermore, this study addressed concerns raised by prior research indicating an increased risk of acute kidney injury (AKI) associated with inhaled NO therapy. While the incidence of AKI was high in both study arms, it was not significantly different, suggesting that inhaled NO did not increase the risk of AKI or the need for kidney replacement therapy. However, the study’s relatively small sample size precludes definitive conclusions regarding the potential nephrotoxicity of inhaled NO, necessitating further investigation through larger trials.
Notably, this trial differed from earlier studies in several ways. It included a more homogeneous population of patients with acute hypoxic respiratory failure specifically due to COVID-19 pneumonia, avoiding the heterogeneity observed in previous ARDS trials. Additionally, this study adhered to protective lung ventilation strategies, in contrast to earlier trials employing potentially injurious ventilation methods. The implementation of low tidal volume and low airway pressure ventilation likely contributed to the sustained improvement in oxygenation observed in this trial.
At a pathophysiological level, COVID-19 pneumonia is characterized by severe endothelial injury, widespread thrombosis, and microangiopathy in pulmonary vessels. Inhaled NO therapy might help mitigate NO deficiency observed in COVID-19 patients, directly alleviating intrapulmonary shunting and improving pulmonary blood flow, ultimately sustaining oxygenation. Improved ventilatory ratios in patients receiving inhaled NO further suggest reduced alveolar dead space, possibly due to the anti-platelet and anti-leukocyte adhesion properties of NO.
Moreover, a subset of participants with daily sputum and plasma sampling for SARS-CoV-2 viral load estimation exhibited faster viral clearance and reduced viral load in sputum with inhaled NO. The antiviral effects of NO are dose-dependent, as evidenced by laboratory studies demonstrating inhibition of SARS-CoV-2 replication through nitrosation of viral membrane proteins and hindrance of viral protease. These findings align with previous research demonstrating NO’s antiviral activity against various pathogens, including influenza, coxsackie, and SARS-CoV-1.
Additionally, in the context of growing evidence of COVID-19-related neuroinflammation and long-term neurological consequences, participants receiving inhaled NO exhibited reduced rates of sensory symptoms at 90 days. This effect may stem from inhaled NO’s systemic anti-inflammatory and anti-thrombotic responses. However, further research is required to delve into the mechanisms and impact of inhaled NO on neurological outcomes, as persistent neurological deficits are a significant concern for survivors of ARDS and severe COVID-19 infection.
Limitations
Several limitations of this study warrant discussion. Firstly, the study’s relatively small phase II design did not possess the power to definitively assess the impact of inhaled NO on mortality. Larger phase III trials are required to evaluate this critical outcome. Secondly, the absence of blinding and the lack of a placebo in the control group were deliberate measures to protect healthcare workers from COVID-19 exposure during the early stages of the pandemic when vaccines were unavailable. Similarly, baseline levels of right heart dysfunction were not obtained to minimize healthcare workers’ exposure to COVID-19. Thirdly, the trial focused exclusively on critically ill patients with COVID-19 pneumonia, limiting the generalizability of the results to other causes
Conclusions
This multicenter, phase II, single-blind, randomized, controlled trial has provided valuable insights into the potential benefits and safety of high-dose inhaled nitric oxide (NO) therapy in mechanically ventilated critically ill patients suffering from acute hypoxemic respiratory failure due to COVID-19 pneumonia. The study’s comprehensive analysis and exploration of various clinical parameters have yielded several key findings and implications for future research and clinical practice.
- Improved Oxygenation: One of the central findings of this study is that high-dose inhaled NO at a concentration of 80 ppm, administered within the first 48 hours of mechanical ventilation, led to a significant improvement in the PaO2/FiO2 ratio. This improvement indicates enhanced systemic oxygenation in patients with acute hypoxemic respiratory failure due to COVID-19 pneumonia, as compared to those who received usual care alone.
- No Reduction in Mortality: Despite the improvement in oxygenation, the study did not observe a statistically significant reduction in mortality among patients treated with inhaled NO. This suggests that while inhaled NO may enhance oxygenation, it may not directly influence overall survival in critically ill COVID-19 patients.
- Reduction in Viral Load: An intriguing finding was the steeper reduction in plasma viral load observed in patients who received inhaled NO. This suggests that high-dose inhaled NO may have antiviral properties that contribute to the faster clearance of the SARS-CoV-2 virus. Given the link between viral load and disease severity, this reduction in viral load is a promising avenue for further investigation and potentially a key factor in improving clinical outcomes.
- Neurological Benefits: The study also noted a reduction in sensory neurologic symptoms and signs at 90 days in participants treated with inhaled NO. This is significant considering the increasing recognition of neurologic complications associated with COVID-19. It suggests that inhaled NO may have neuroprotective properties, which warrant further exploration in future studies.
- Safety and Tolerance: Importantly, the administration of high-dose inhaled NO was well-tolerated by the study participants, and no serious adverse events related to the intervention were reported. This underscores the safety profile of inhaled NO therapy, even at elevated doses.
In conclusion, this study adds to the growing body of evidence suggesting the potential benefits of high-dose inhaled NO therapy for critically ill COVID-19 patients with acute hypoxemic respiratory failure. While it did not demonstrate a reduction in mortality or duration of mechanical ventilation, it did show significant improvements in oxygenation, a reduction in viral load, and potential neuroprotective effects. These findings highlight the need for further dose-response investigations into the antimicrobial and clinical properties of high-dose inhaled NO therapy in adults with acute hypoxemic respiratory failure.
The results of this study provide a foundation for designing larger, more robust phase III trials to confirm and expand upon these findings. Such trials will be crucial in determining the precise role of high-dose inhaled NO in the management of COVID-19 and its potential to improve patient outcomes in the face of this ongoing global health challenge.
reference link :https://www.atsjournals.org/doi/epdf/10.1164/rccm.202304-0637OC?role=tab
