Inhaled Pulmonary Vasodilators in COVID-19 Infection: A Systematic Review and Meta-Analysis

Introduction: Inhaled pulmonary vasodilators (IPVD) have been previously studied in patients with non-coronavirus disease-19 (COVID-19) related acute respiratory distress syndrome (ARDS). The use of IPVD has been shown to improve the partial pressure of oxygen in arterial blood (PaO₂), reduce fraction of inspired oxygen (FiO₂) requirements, and ultimately increase PaO₂/FiO₂ (P/F) ratios in ARDS patients. However, the role of IPVD in COVID-19 ARDS is still unclear. Therefore, we performed this meta-analysis to evaluate the role of IPVD in COVID-19 patients. Methods: Comprehensive literature search of PubMed, Embase, Web of Science and Cochrane Library databases from inception through April 22, 2022 was performed for all published studies that utilized IPVD in COVID-19 ARDS patients. The single arm studies and case series were combined for a 1-arm meta-analysis, and the 2-arm studies were combined for a 2-arm meta-analysis. Primary outcomes for the 1-arm and 2-arm meta-analyzes were change in pre- and post-IPVD P/F ratios and mortality, respectively. Secondary outcomes for the 1-arm meta-analysis were change in pre- and post-IPVD positive end-expiratory pressure (PEEP) and lung compliance, and for the 2-arm meta-analysis the secondary outcomes were need for endotracheal intubation and hospital length of stay (LOS). Results: 13 single arm retrospective studies and 5 case series involving 613 patients were included in the 1-arm meta-analysis. 3 studies involving 640 patients were included in the 2-arm meta-analysis. The pre-IPVD P/F ratios were significantly lower compared to post-IPVD, but there was no significant difference between pre- and post-IPVD PEEP and lung compliance. The mortality rates, need for endotracheal intubation, and hospital LOS were similar between the IPVD and standard therapy groups. Conclusion: Although IPVD may improve oxygenation, our investigation showed no benefits in terms of mortality compared to standard therapy alone. However, randomized controlled trials are warranted to validate our findings.