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Role of operating room size on air quality in primary total hip arthroplasty

December 2023
The Center For Health Design


Why does this study matter?
We started to learn more about OR design 10 years ago with the publication of the first RIPCHORD project about cardiac surgeries. The work was expanded through a grant conducted at Clemson. It was a systems approach with findings about flow disruptions, movement in the OR, and implications for both size and table orientation. There were sub-studies that looked at microbial load related to the combination of people, movement, and door openings.

Other research has evaluated HVAC systems, often mock-ups or simulations, and UV light. So we know quite a bit, but surgical site infections, or SSIs, are still a problem, especially with orthopedic procedures. They can have significant financial costs, as well as the cost of negative outcomes like morbidity and mortality.

How was the study done?
These were both retrospective studies of EHR data for elective surgeries at the same academic medical center. The setting was two ORs - the smallest and largest ORs being used in the facility. Each had the same HVAC system and was already equipped with a UV HEPA filtration device to reduce particulates in the OR. In one study, researchers looked at total knee replacement (arthroplasties) for about 14 months. In the other, the team looked at total hip replacements (arthroplasties) for the same time period. There were about 2 months of procedures that were excluded due to COVID-related policies.

Measurements of temperature, humidity, and airborne biologic particle counts per minute were recorded by the filtration device in each OR. Why particulate counts? As costly as orthopedic SSIs are, the incidence rates are low, usually under 2%, so it’s hard to create a controlled study about SSIs for orthopedic procedures. Since research has demonstrated that airborne particles are linked to bacterial concentrations, particle counts are often used as a proxy for SSIs. This is a correlation study of indirect results based on statistical tests of change.     

So what do we learn from the study?
Let’s look at the results. For the total knee procedure, most, 77%, were performed in the large OR. There were significant differences in relative humidity, but not in the temperature or total time in the OR. For airborne particulate measures, there was a significant decrease for average biologic particles per minute for particles sizes of 2.5 and 5.0 microns in the large compared to the small OR.
Like the total knee, most of the total hip procedures were performed in the large OR, in this case, 84.5%. Unlike the knee procedures, there were significant differences in temperature and total time in the OR, in addition to relative humidity. In this set of cases, there were significant decreases in rates for the particles per minute for particles measuring 2.5, 5.0, and 10.0 microns in the large OR compared to the small OR.  

Can we say the results are definitive?
While these two studies are simple and straightforward, that comes with limitations. First and foremost, the study doesn’t measure SSIs, like I already talked about, and the team also measured average particle count per minute, not a cumulative load. An advantage of this study, is that it’s not a simulation or modeling. It’s a real environment, with a procedure, a patient, surgical team, although their movements and characteristics weren’t specifically accounted for. There’s no risk adjustment, but that’s more suited for a clinical outcome versus straight particle counts.

What we definitively know from this study that the filtration system was subject to a lower particle burden in the larger OR. What is suggested by the study is that, given other factors being “assumed” the same, OR size alone MIGHT be a contributing factor to SSI. There are studies that have found correlations between the number of particles of 1-5 microns and airborne bacteria levels. Another also found a relationship between particle counts and bacterial load and then bacterial load to HAIs. There are other studies that have actually measured SSIs with respect to OR size, but with conflicting results. Neither measured particle counts, so we’re missing that connection between studies. So just like increased particulate counts from fires in some parts of the world earlier this year, the results are a little hazy.

What’s the takeaway?
Which brings me to my takeaway. A lot of times we talk about diffusion – diffusion of innovations, diffusion of ideas or knowledge. In this case, we can make a literal interpretation. The filtration system recorded a lower particle burden in larger rooms. The particles can diffuse with more volume and area. To me, these results make intuitive sense. It’s specific studies, like these, along with the others we have, that get us closer to the meaningful answers we’re looking for. And that gets back to the diffusion of ideas. So at the end of the day, this snapshot is about both literal and figurative diffusion. 


Summary of:
Derry, K. H., Sicat, C. S., Shen, M., Davidovitch, R. I., Schwarzkopf, R., & Rozell, J. C. (2023). Role of Operating Room Size on Air Quality in Primary Total Hip Arthroplasty. The Journal of Arthroplasty, Issue 5, Volume 38, Page(s) 935–938. https://doi.org/10.1016/j.arth.2022.12.011



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