Medical air in healthcare institutions: A chemical and biological study

A significant proportion of hospitalized patients are dependent on medical air. Medical air is commonly produced on-site from filtered and compressed external air before delivery to patients through centralized piping. Little is known about how outside ambient air composition can affect medical air quality. This study examined how chemical and microbial content of medical air varied at the delivery ports as a function of ambient air. The chemical composition was monitored near the outdoor air intake and at the indoor outlet in a patient room of a healthcare center. The microbial content was determined twice weekly using a custom-made impaction device designed for pressurized systems. Results revealed some chemical gases are not well filtered by the medical air system; the average concentrations of CO and CO2 in this medical air (160 ppb and 442 ppm) were similar to outdoor concentrations, indicating that these gases pass freely to bedside outlets. NOx and O3 are only 40% removed yielding average concentrations of 16 and 10 ppb in this medical air. Trace metals could also be detected. Bacteria were detected, but at concentrations significantly lower than 1 colony forming unit (CFU) per m3 of medical air sampled; these consisted predominantly of non-pathogenic bacteria. This study highlights the impact of changes in outdoor air quality on the composition of medical air delivered to patients, and the importance of monitoring and regulating the quality of medical air.