Impact of Prefecture-level Intensive Care Unit Congestion on Mortality in Severe COVID- 19 Patients: A Retrospective Observational Study in Japan

Background The COVID-19 pandemic has placed unprecedented pressure on global healthcare systems, severely affecting the intensive care unit (ICU) capacity. Therefore, this study explored the association between prefecture-level ICU congestion and COVID-19 mortality in each prefecture of Japan. Methods This retrospective study analyzed data from the CRoss Icu Searchable Information System, covering all patients with COVID-19 who required mechanical ventilation or extracorporeal membrane oxygenation between January 1, 2020, and March 31, 2023. Prefecture-level ICU congestion was calculated as the total ventilator days over 2 weeks for severely ill patients with COVID-19, divided by the maximum potential ventilator days in the prefecture. Prefecture-level ICU congestion in each region was visualized by plotting time-series graphs capturing the temporal progression of congestion levels. A mixed-effects logistic regression model was fitted to evaluate the association between prefecture-level ICU congestion and mortality. Results A total number of 10,046 patients were included in this study, and the mortality rate was 23.2%. Congestion levels varied by time and prefecture, ranging from 0 to over 1.5, indicating a strain beyond capacity. Median congestion level (interquartile range [IQR]) at admission was 0.3 (0.1, 0.6), and increased congestion level was statistically associated with increased mortality (odds ratio: 1.14; 95% confidential interval: 1.08–1.21). Conclusions Increased prefecture-level ICU congestion may be associated with increased COVID-19 mortality, warranting further investigation.