Am. J. Respir. Crit. Care Med., Vol 152, No. 6, Dec 1995, 1992-1999.
Measuring ventilation of patient care areas in hospitals. Description of a new protocol
R Menzies, K Schwartzman, V Loo and J Pasztor
Montreal Chest Institute, Quebec, Canada.
It has been recommended that ventilation of health care facilities should
be monitored regularly to reduce the risk of nosocomial transmission of
tuberculosis. We developed a simple method to measure air-change rates and
direction of airflow in patient care areas. Pure carbon dioxide (CO2) was
released at 13.5 L/min for 5 min, then measured for 30 min within the room
and outside in the hallway. Smoke tubes were also used to measure direction
of airflow. Doors and windows (if openable) were manipulated. This
protocol, when conducted in five offices in 30 patients care areas in two
hospitals, provided good mixing and reproducible decay curves, with less
than 15% coefficient of variation for repeated measures over a wide range
of air-change rates. Manipulation of door and/or window produced
significant changes in air- change rates and airflow direction, although
calculated air-change rates were more variable. Smoke tube measurements
were inconsistent, agreed poorly with evidence of CO2 movement from room to
hall, and were strongly affected by room to hallway temperature
differentials. CO2 release and measurement proved to be a simple, yet
reliable, method to measure air-change rates and the effect of door or
window manipulation. Smoke tube measurements were not reliable to
characterize direction of airflow.
