Monitors to improve indoor air carbon dioxide concentrations in the hospital: A randomized crossover trial

BACKGROUND: Ventilation has emerged as an important strategy to reduce indoor aerosol transmission of coronavirus disease 2019. Indoor air carbon dioxide (CO(2)) concentrations are a surrogate measure of respiratory pathogen transmission risk. OBJECTIVES: To determine whether CO(2) monitors are necessary and effective to improve ventilation in hospitals. METHODS: A randomized, placebo (sham)-controlled, crossover, open label trial. Between February and May 2021, we placed CO(2) monitors in twelve double-bed patient rooms across two geriatric wards. Staff were instructed to open windows, increase the air exchange rate and reduce room crowding to maintain indoor air CO(2) concentrations ≤800 parts per million (ppm). RESULTS: CO(2) levels increased during morning care and especially in rooms housing couples (rooming-in). The median (interquartile range, IQR) time/day with CO(2) concentration > 800 ppm (primary outcome) was 110 min (IQR 47–207) at baseline, 82 min (IQR 12–226.5) during sham periods, 78 min (IQR 20–154) during intervention periods and 140 min (IQR 19.5–612.5) post-intervention. The intervention period only differed significantly from the post-intervention period (P = 0.02), mainly due to an imbalance in rooming-in. Significant but small differences were observed in secondary outcomes of time/day with CO(2) concentrations > 1000 ppm and daily peak CO(2) concentrations during the intervention vs. baseline and vs. the post-intervention period, but not vs. sham. Staff reported cold discomfort for patients as the main barrier towards increasing ventilation. DISCUSSION: Indoor air CO(2) concentrations in hospital rooms commonly peaked above recommended levels, especially during morning care and rooming-in. There are many possible barriers towards implementing CO(2) monitors to improve ventilation in a real-world hospital setting. A paradigm shift in hospital infection control towards adequate ventilation is warranted. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04770597