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

Ventilation has emerged as an important strategy to reduce indoor aerosol transmission of coronavirus disease 2019. Indoor air carbon dioxide (CO₂) concentrations are a surrogate measure of respiratory pathogen transmission risk.

To determine whether CO₂ monitors are necessary and effective to improve ventilation in hospitals.

A randomized, placebo (sham)-controlled, crossover, open label trial. Between February and May 2021, we placed CO₂ 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 CO₂ concentrations ≤800 parts per million (ppm).

CO₂ levels increased during morning care and especially in rooms housing couples (rooming-in). The median (interquartile range, IQR) time/day with CO₂ 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 CO₂ concentrations > 1000 ppm and daily peak CO₂ 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.

Indoor air CO₂ concentrations in hospital rooms commonly peaked above recommended levels, especially during morning care and rooming-in. There are many possible barriers towards implementing CO₂ monitors to improve ventilation in a real-world hospital setting. A paradigm shift in hospital infection control towards adequate ventilation is warranted.

ClinicalTrials.gov Identifier: NCT04770597.