Substance Use and Delirium Trends in the Critically Ill During the Peri-COVID Period

Substance use complicates many hospitalizations by increasing delirium rates, acuity, and costs. Its prevalence rose during the COVID-19 pandemic, potentially contributing to increased delirium in hospitalized patients.

To describe trends in substance use and delirium complicating ICU and floor admission around the COVID-19 pandemic and determine whether increased societal substance use was associated with increased prevalence of delirium and substance use in the critically ill.

Retrospective cohort study using a large deidentified database of patients admitted to the medical ICU and medicine wards at a single U.S. academic center. We used International Classification of Diseases, Tenth Revision (ICD-10) codes for substance use and a validated ICD-based delirium phenotype to identify exposures.

Monthly prevalence of delirium and substance use was calculated in the ICU and on the floor. We performed interrupted time series analysis to determine the effect of the COVID-19 pandemic on these trends.

Pre-pandemic, ICU admissions complicated by substance use were declining. The onset of COVID-19 marked a significant reversal, with stepwise continued increase upon entering the recovery phase of the pandemic. Floor admissions complicated by substance use were gradually decreasing pre-pandemic, remained steady during lockdowns, and rose in the recovery phase. ICU delirium prevalence was decreasing pre-pandemic but rose abruptly with the onset of lockdowns, then declined during the pandemic. Delirium prevalence on the floor was increasing before the pandemic and remained stable during the peak and has continued to rise into the recovery phase.

Post-COVID, substance use increased in both ICU and floor admissions. Delirium increased during COVID but has since decreased in the ICU. Prevalence has continued to rise on the floor. Substance use and delirium trends during the COVID-19 pandemic reflect strain on the healthcare system during this time.