There might be a serial-killer in our hospitals! (Part 2)

In this technical paper from Nortec, we continue looking at the importance of air humidification in hospitals and in outpatient settings. This article by Stephanie Taylor (CEO of Taylor Healthcare Consulting) was included in the paper and looks at healthcare associated infections.

Part 1 - of the Healthy air humidity series
Part 3 - Healthy air humidity

To get a better understanding of the relationship between indoor air parameters in patient rooms and the incidence of HAIs, a study was recently done in a newly constructed, approximately 250-bed academic hospital in the north-central US. Over a 13-month period, hourly measurements of room temperature, absolute and relative humidity, lighting levels (lux), room air changes, outdoor ventilation fractions, carbon dioxide levels, and room traffic were monitored in 10 patient rooms.

During this same period, electronic medical records of patients admitted to these rooms were analysed for the presence of HAIs. Multi-variable statistical analysis was then run on the data to determine if any indoor conditions independently correlated with these patient infections. Of all the environmental measurements tracked and correlated with patient outcomes, indoor relative humidity (RH) was found to be the most significantly related to HAI rates. These startling results clearly show that patient room RH was inversely proportional to HAIs (p< 0.02) in other words, as indoor RH increased, the patient HAI rate decreased!

To best protect patient health, optimise clinical outcomes and decrease excess healthcare costs, the indoor relative humidity (RH) must be maintained between 40 and 60%.

These findings reinforce the need to understand, monitor, and manage indoor air hydration, or humidification, to decrease patient HAIs.

Clearly, pathogens fare poorly in properly hydrated air, people are much healthier! What are the reasons for this?

Human lung physiology demands provision of 100% saturated air heated to 98.6 degrees Fahrenheit for their essential function: gas exchange. In the lungs, inhaled oxygen is exchanged for the metabolic waste product carbon dioxide across delicate, one cell membranes of the alveoli. Deep in the lung tissue, fragile alveoli sacs are in close proximity to blood vessels. To prevent infectious particles from settling into the alveoli where pneumonia or systemic blood infections could easily result, physiological barriers trap particulate matter in the upper regions of the respiratory system.

Ambient air moisture is necessary for optimal functioning of this defensive mechanism. Respiratory mucosa from the nose to the small bronchial tubes moistens and heats inhaled air before it reaches the alveoli. When ambient air is dried to RH of 20%, patients lose 60 to 80g/hour (1½ to 2 litres/day) of water. The water loss by airways alone is 300 to 500 millilitres per day.

In addition to drying the upper respiratory tract mucosa and reducing clearance of infectious droplets, the patient struggles to maintain adequate hydration needed for immune cell functioning and wound healing.

Healthcare associates infectionsHealthcare associated infections in 10 monitored rooms.


The hospital’s physical environment has a significant impact on the health of patients. Unfortunately, too many patients are harmed and hospitals waste money on avoidable HAIs.

The dry air in most hospitals create habitats for microorganisms that are unprecedented in the natural world and have untold consequences for the selection and transmission of pathogens. By maintaining RH in patient care spaces between 40 and 60%, the transmission and infectivity of airborne pathogens will be reduced, and surface cleaning will be more effective due to less resuspension and redeposition of pathogens. In addition to creating a less infectious environment, indoor air hydration will support patients’ physiologic skin and respiratory tract defences, immune cell functioning, wound healing, and total body fluid balance — all natural defences against HAIs.

Current indoor air guidelines for hospitals do not specify a lower limit RH in patient care areas and are even promoting lowering the minimum acceptable RH level in operating rooms from the current 35% down to 20%. This is a mistake! Management of healthcare facilities must focus on the number one priority: patient healing.

To best protect patient health, optimise clinical outcomes, and decrease excess healthcare costs, the indoor RH must be maintained between 40 and 60%. This exciting new data on the influence of hospital indoor air on healthcare-associated infections, and consequently, on patient outcomes, gives hospital engineers and building managers new tools to ensure the best possible outcomes for patient healing.

*To be continued

**Republished with permission.


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