For decades, ventilation has been at the centre of efforts to control airborne contamination in surgical settings. However, growing evidence and practical challenges have made something very clear; ventilation alone is not enough. The conversation must expand to include filtration as a fundamental pillar of indoor air quality in operating theatres. This article explores the interplay between ventilation and filtration in operating theatres, why the latter is often overlooked and how integrated solutions that are both smart and sustainable can better protect patients and staff while supporting long term operational goals.
Why clean air matters more than ever
Airborne contaminants in operating theatres originate from people (staff and patients), equipment and even the air supply itself. These microscopic particles are often invisible to the naked eye but can carry bacteria, viruses and other pathogens. When they settle into open surgical sites, they can cause serious post-operative infections. Healthcare-associated infections (HCAIs) remain a critical priority for all healthcare facilities. Despite significant progress in infection control, the problem persists. According to the BMJ,1 an estimated 4.7per cent of adult inpatients in general and teaching hospitals across England acquired an HCAI in 2016-17, costing the NHS approximately £2.1 bn.2
The consequences of HCAIs extend well beyond the financial. These infections often lead to prolonged hospital stays, the need for additional surgery, staff absences, and considerable emotional and physical strain on patients and their families. They are responsible for around 5.6 million occupied hospital bed days, 62,500 staff absences, and 22,800 patient deaths each year.2
Among the various types of HCAIs, Surgical Site Infections (SSIs) are among the most common, accounting for 15.7% of all reported cases. These infections are associated with a 34%-226% increase in treatment costs, due to prolonged hospital stays, readmissions and the need for re-operations. SSIs not only compromise patient safety and recovery but also place considerable financial strain on the NHS.3
Ventilation alone is not enough
Operation theatres rely on ventilation systems like laminar airflow (LAF) or ultraclean ventilation (UVC) to reduce airborne contamination. These systems typically use directional airflow, high air change rates and built-in HEPA filters to help limit the spread of contaminants. However, the cleanest airflow is usually concentrated over the surgical site and instrument table and not the entire room. As a result, areas outside the direct airflow zone may not receive the same level of protection.4 Ventilation systems, even when well-designed, cannot guarantee that airborne particles and pathogens are consistently removed from every part of the room. While ventilation moves the air, it is filtration that removes harmful contaminants.
Real-world factors such as staff movement, equipment placement, and ageing infrastructure can disturb the airflow patterns and allow contaminants to accumulate in areas beyond the direct ventilation zone.5 Studies have shown that portable HEPA filtration units can significantly reduce aerosol concentrations, particularly in settings where existing systems are under strain or inconsistently maintained.6
Supplementary filtration can also play a crucial role in improving air quality in high-risk zones that sit outside the optimal reach of built-in systems. In fact, research has found that portable air purifiers can significantly reduce airborne aerosol concentrations, even when used alongside standard ventilation. This suggests they may help lower the risk of airborne infection in healthcare settings where ventilation alone falls short of providing adequate protection.6,7
What is needed is a complimentary approach: ventilation to move air and filtration to clean it. Together, they offer a more complete solution to protect high-risk spaces like the operation theatre. Supplementary HEPA filtration offers a practical, evidence-based layer of defence, particularly in older theatres or during periods of high demand.
High-Efficiency Particulate Air (HEPA) filters are capable of trapping 99.97% of airborne particles as small as 0.3 microns. This includes bacteria, viruses, fungal spores, and dust. When paired with effective ventilation, HEPA filtration significantly reduces airborne contaminant levels and improves the air quality in operation theatres.
Multiple peer-reviewed studies support the value of filtration. A study published in the Journal of Hospital Infection found that operating theatres with integrated HEPA filtration had significantly lower bacterial counts than those relying on standard ventilation alone.8
Another report in BMJ Open Respiratory Research confirmed the benefits of portable HEPA filtration units in rapidly clearing airborne particles from enclosed hospital spaces.9
Filtration is not just a clinical improvement; it’s a strategic one. Cleaner air leads to fewer complications, which in turn shortens recovery times and reduces demand on already stretched bed capacity. In many ways, investing in filtration is less about adding something new and more about filling a gap that can no longer be ignored.
It also provides a buffer against variables that ventilation alone can’t manage. Whether it’s a door left open too long or an unexpected spike in theatre activity, filtration ensures the air is still being cleaned. That kind of reliability is not just helpful, it’s vital. It takes pressure off clinical teams and gives estate teams more control over indoor air quality. The takeaway? Filtration improves air quality at a level that ventilation alone simply cannot achieve.
While Smart Air’s Blast air purifiers are not a replacement for true laminar airflow (LAF) systems, hospitals in South Asia have successfully used them as a supplementary air quality measure in operating theatres lacking dedicated ultraclean ventilation (UCV). By strategically placing two Blast units to create a controlled directional airflow, these purifiers help reduce airborne contaminants in the surgical zone. This approach demonstrates how filtration can play a vital role in maintaining cleaner surgical environments, especially in theatres without specialised airflow systems.
Advanced filtration systems can be deployed with minimal disruption in a range of ways depending on facility size, infrastructure, and budget. These include:
- Portable HEPA units: These standalone units can be easily deployed without the need for invasive installation or changes to the existing HVAC system. They are ideals for ad hoc upgrades, temporary surgical areas, or as supplementary protection in high-risk scenarios. Their flexibility makes them particularly useful during times of increased demand, such as during respiratory virus seasons or outbreaks.
- Ceiling-mounted filtration systems: These systems integrate with the theatre ceiling and continuously clean air within the room. They are more permanent than portable units and are often installed in wards and consulting rooms. While they may require some infrastructural modifications, they provide continuous air purification without occupying floor space which is critical in maintaining theatre workflows.
- Air Handling units (AHU) upgraded filtration: Portable HEPA air filters in AHU rooms ensures that filtered air is delivered to theatres via existing ductwork. This method offers a more centralised and scalable solution.
Flexibility is key. Filtration does not need to delay theatre schedules or trigger estates-wide upheaval.
Sustainability and cost-efficiency
Many Trusts have an immense pressure to improve clinical standards while reducing environmental impact. Smart filtration systems are increasingly helping address both these issues. Traditional HVAC overalls can be expensive, time-consuming and highly disruptive. In contrast, adding or upgrading filtration systems — especially the portable air purifiers or ceiling-mounted units — provide a faster, less costly way to improve air quality without ripping out existing infrastructure.
From an environmental perspective, deploying the Blast and the Blast Mini, with the additional smart module at hospitals can significantly help reduce power consumption while delivering clean air at full capacity. The smart module helps the units to operate at full capacity when needed, while helping reduce electricity use compared to older, always-on HVAC systems. This helps hospitals move towards Net Zero goals while still prioritising clinical safety. The technology is compliant with HTM-03 recommendations (UKCA, EN 1822-1:2019, EN ISO 294633:2018). Moreover, by reducing the risks of SSIs, smart filtration indirectly cuts down on hospital stays, antibiotic use and repeated procedures. This represents a significant cost saving for the NHS and frees up valuable resources. In a two-year study at a UK NHS Trust, a reduction in SSI saved the NHS added a median 10 days to hospital stay and cost the Trust approximately £5,239 per case, adding up to an extra £2.4 m overall.11
Ultimately, improving air quality in theatres is not just a technical challenge, it’s a cultural one. Staff must understand the limitations of ventilation and the value of filtration. Infection control teams, estate managers, surgeons and procurement teams all have a role to play in championing smarter air quality solutions.
Training and awareness are key. From clinical directors to theatre staff, understanding the role of HEPA filters, the value of smart monitoring and how to respond to air quality data can ensure systems are used to their full potential.
Conclusion
Operation theatres are no place for compromise. Clean air is non-negotiable in such a high-stakes environment where every detail matters. While ventilation has served as the traditional guardian of air quality, it cannot stand alone. Filtration must now be part of the conversation.
We’ve reached a point where the question is no longer “Can we afford to add filtration?” but rather “Can we afford not to?” Every preventable infection avoided, every hospital bed freed up, every patient who recovers without complication is a win, not just for the hospital but for the entire healthcare system.
Filtration must be recognised as a safety measure, as well as a strategic investment in sustainable patient care. From portable units that provide quick wins to integrated AHU upgrades and intelligent monitoring systems, the tools are available, accessible and scalable. As Trusts and estate teams look to achieve infection control, as well as achieve Net Zero, filtration offers a pragmatic, impactful and cost-effective solution.
Investing in filtration isn’t about ticking boxes; it’s about using the tools we already have to do better for patients, for staff and for the system. It is time to stop treating filtration as an optional extra and start recognising it as essential to safe, modern and sustainable surgical care.
References
1 Guest JF et al. (2020) Modelling the annual NHS costs and outcomes attributable to healthcare-associated infections in England, BMJ Open. Available at: https://bmjopen.bmj.com/content/10/1/e033367 (Accessed: 05 June 2025).
2 Healthcare Design & Management. (n.d.). Controlling airborne contamination within operating theatres. Healthcare Design & Management. Retrieved June 5, 2025, from https://www.healthcaredm.co.uk/controlling-airborne-contamination-within-operating-theatres.
3 Preventing surgical site infections (2023) Health Innovation West of England. Available at: https://www.healthinnowest.net/our-work/transforming-services-and-systems/ preventing-surgical-site-infections/ (Accessed: 05 June 2025).
4 (2021) Operating room ventilation systems: Recovery degree, Cleanliness Recovery Rate and air change effectiveness in an ultra-clean area. Journal of Hospital Infection. Available at: https://www.journalofhospitalinfection.com/article/S0195-6701(21)00459-X/fulltext (Accessed: 07 June 2025).
5 Wang Q et al. (2020) Association of Laminar airflow during primary total joint arthroplasty with periprosthetic joint infection, JAMA Network Open, 3(10). doi:10.1001/jamanetworkopen.2020.21194.
6 Salmonsmith J et al. (2023) Use of portable air purifiers to reduce aerosols in hospital settings and cut down the clinical backlog, Epidemiology and Infection. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC9990385/ (Accessed: 06 June 2025).
7 Health Technical Memorandum 03-01. Specialised ventilation for healthcare premises Part A: The concept, design, specification,installation and acceptance testing of healthcare ventilation systems (no date) England NHS. Available at: https://www.england.nhs.uk/wp-content/uploads/2021/05/HTM0301-PartA-accessible-F6.pdf (Accessed: 07 June 2025).
8 Fennelly M et al (2023), Portable HEPA filtration successfully augments natural-ventilation-mediated airborne particle clearance in a Legacy Design Hospital Ward, Journal of Hospital Infection, 131, pp. 54—57. doi:10.1016/j.jhin.2022.09.017.
9 Falkenberg T et al. (2023) ‘Effect of portable HEPA filters on COVID-19 period prevalence: An observational quasi-interventional study in German kindergartens’, BMJ Open, 13(7). doi:10.1136/bmjopen-2023-072284.
10 NHS Estates Technical Bulletin (NETB 2023/01A): application of HEPA filter devices for air cleaning in healthcare spaces: guidance and standards, NHS. Available at: https://www.england.nhs.uk/long-read/application-of-hepa-filter-devices-for-air-cleaning-in-healthcare-spaces-guidance-and-standards/ (Accessed: 06 June 2025).
11 R;, J.P.M.S. Clinical and economic burden of surgical site infection (SSI) and predicted financial consequences of elimination of SSI from an English hospital, Journal of Hospital Infection. Available at: https://pubmed.ncbi.nlm.nih.gov/24268456/ (Accessed: 06 June 2025).
Acknowledgement
n This article was originally prepared for HEJ’s sister publication, Clinical Services Journal. We are grateful to CSJ’s Editor Louise Frampton for kindly permitting its inclusion in this month’s issue.