Comparative analysis of COVID-19 critically ill patients across four pandemic waves in Greece.

Introduction: There is limited information about trends in mortality of intensive care unit (ICU) patients with Coronavirus Disease-2019 (COVID-19) throughout the entire pandemic period. Aim: We compared the ICU mortality among the four consecutive waves of the pandemic, according to the virus variant predominance. Methods: This is a retrospective study of prospectively collected data extracted from our COVID-19 clinical database. All adult patients with confirmed SARS-CoV-2 infection, consecutively admitted to our ICU from March 2020 through April 2022, were included. For the analysis we used the dates of the four periods of the pandemic, according to the predominance of different SARS-CoV-2 variants in Greece. Kaplan-Meier and Cox proportional hazards analyses were used. Results: In total, 805 patients [median (IQR) age 67 (56-76) years, 68% males] were included. APACHE II, Charlson, and SOFA scores were 14 (11-19), 3 (2-5) and 7 (4-9), respectively; 674 (84%) patients required invasive mechanical ventilation. ICU length of stay was 15 (8-29) days, and mechanical ventilation duration was 11 (4-24) days. ICU and hospital mortality was 48% and 54%, respectively. Kaplan-Meier survival curves revealed no significant differences in ICU mortality among the four waves. Age, malignancy, chronic pulmonary disease and SOFA score were independent predictors of ICU mortality, but the pandemic waves themselves were not. Age had a significant impact on ICU mortality across all waves. Conclusion: The effect of COVID-19 wave (and consequently of the SARS- CoV-2 variant) on ICU mortality seems to be trivial, and therefore our focus should be shifted to other risk factors, such as age and comorbidities. These findings along with those of other studies could be useful for modelling the evolution of future outbreaks.