A narrative review of COVID-19-related acute respiratory distress syndrome (CARDS): “typical” or “atypical” ARDS?

BACKGROUND AND OBJECTIVE: The coronavirus disease of 2019 (COVID-19) is highly infectious and mainly involves the respiratory system, with some patients rapidly progress to acute respiratory distress syndrome (ARDS), which is the leading cause of death in COVID-19 patients. Hence, fully understanding the features of COVID-19-related ARDS (CARDS) and early management of this disease would improve the prognosis and reduce the mortality of severe COVID-19. With the development of recent studies which have focused on CARDS, whether CARDS is “typical” or “atypical” ARDS has become a hotly debated topic. METHODS: We searched for relevant literature from 1999 to 2021 published in PubMed by using the following keywords and their combinations: “COVID-19”, “CARDS”, “ARDS”, “pathophysiological mechanism”, “clinical manifestations”, “prognosis”, and “clinical trials”. Then, we analyzed, compared and highlighted the differences between classic ARDS and CARDS from all of the aspects above. KEY CONTENT AND FINDINGS: Classical ARDS commonly occurs within 1 week after a predisposing cause, yet the median time from symptoms onset to CARDS is longer than that of classical ARDS, manifesting within a period of 9.0–12.0 days. Although the lung mechanics exhibited in CARDS grossly match those of classical ARDS, there are some atypical manifestations of CARDS: the severity of hypoxemia seemed not to be proportional to injury of lung mechanics and an increase of thrombogenic processes. Meanwhile, some patients’ symptoms do not correspond with the extent of the organic injury: a chest computed tomography (CT) will reveal the severe and diffuse lung injuries, yet the clinical presentations of patients can be mild. CONCLUSIONS: Despite the differences between the CARDS and ARDS, in addition to the treatment of antivirals, clinicians should continue to follow the accepted evidence-based framework for managing all ARDS cases, including CARDS.