Airflow in an Operating Theatre: Importance and Solutions for Cleanliness and Efficiency

Airflow management in an operating theatre (OT) is a cornerstone of hospital engineering, infection prevention, and patient safety protocols. The objective of an effective airflow system is to minimise the risk of surgical site infections (SSIs) by controlling the concentration and movement of airborne contaminants. Achieving optimal cleanliness while maintaining energy-efficient airflow systems ensures patient safety, staff comfort, and compliance with stringent regulatory standards.

What is Airflow in an Operating Theatre?

Airflow in an operating theatre refers to the controlled movement, filtration, and pressurisation of air within the surgical environment to limit airborne particulate concentration. This involves the coordinated operation of heating, ventilation, and air conditioning (HVAC) systems, equipped with high-efficiency filters, air distribution mechanisms, and pressure control devices. The goal is to maintain a defined airflow pattern that directs clean, filtered air towards the surgical field while removing contaminated air efficiently.

Key Technical Components of Operating Theatre Airflow Systems

• Supply Air Diffusers: Distribute clean, filtered air into the OT, often through laminar flow ceiling arrays or perforated panels.
• Exhaust Grilles: Located near the floor or walls to capture and remove contaminated air.
• HEPA Filters: Installed at air supply points, capable of removing 995% of particles 0.3 microns.
• Pressure Control Systems: Maintain appropriate pressure differentials to prevent cross-contamination.
• Airflow Visualisation Tools: Use smoke or tracer gas to verify airflow patterns during commissioning and routine checks.

Related: The Critical Role of Air Quality in Healthcare Facilities

Types of Airflow Systems

1. Laminar Airflow (LAF): Provides a unidirectional low of filtered air at velocities between 0.3 to 0.5 m/s. Vertical LAF systems direct air downward from ceiling diffusers over the surgical zone, preventing any infiltration of contaminants into the surgical zone. LAF is critical in procedures requiring ultra-clean environments, such as joint replacements and implant surgeries.
2. Turbulent Mixing Airflow: Delivers air through diffusers that mix clean and room air, diluting contaminants rather than displacing them. Although less efficient in reducing particle load compared to LAF, it is cost-effective for general surgeries.
3. Mixed Flow Systems: Utilise a combination of laminar and turbulent flow to provide both dilution and displacement effects, allowing for flexible use in multifunctional surgical suites.

Why is Airflow Important in an Operating Theatre?

1. Infection Control through Particle and Microbial Load Reduction

Airborne particles, often carriers of bacteria, pose significant SSI risks. Studies show that airborne contamination correlates with increased SSI rates. High-quality airflow systems reduce bacterial counts to below 10 CFU/m³ at the surgical site, adhering to international standards such as ISO 14644-1 and EN 14644-2 for cleanroom classifications.

Airflow patterns, including the prevention of recirculation zones and air stagnation, ensure that contaminants from surgical instruments, staff movement, and equipment are continuously flushed away from the sterile field.

Also Read: Inside the World of Cleanrooms: What They Are and Why They Matter

2. Regulatory and Clinical Compliance

Healthcare facilities must comply with national and international guidelines (e.g., ASHRAE 170, HTM 03-01, and WHO surgical safety standards) governing Operating Theatre ventilation. These standards dictate parameters like:

• Air Changes Per Hour (ACH): Typically 20-30 ACH to ensure sufficient air dilution.
• Pressure Differentials: Maintain at least +2.5 Pa between the Operating Theatre and adjacent areas to prevent ingress of contaminated air.
• Temperature and Humidity Control: 18–23°C and 30–60% relative humidity to limit microbial proliferation.

3. Ensuring Patient and Staff Safety

Proper airflow management reduces exposure to volatile anesthetic gases, disinfectant fumes, and biological aerosols, safeguarding both patients and surgical staff. Stable airflow also contributes to staff comfort by mitigating temperature fluctuations and odour build-up.

4. Environmental and Operational Efficiency

Effective airflow systems reduce energy consumption through optimised HVAC designs while maintaining stringent cleanliness standards. Advanced control systems enable variable airflow rates depending on OT occupancy and surgical activity, balancing operational costs with safety requirements.

Solutions to Ensure Cleanliness and Efficient Airflow

Ensuring both cleanliness and efficient airflow requires an integrated approach involving engineering solutions, systematic maintenance, and procedural compliance.

1. High-Efficiency Particulate Air (HEPA) Filtration

HEPA filters with a Minimum Efficiency Reporting Value (MERV) rating of 17 or higher are standard.

2. Positive Pressure Maintenance

Monitoring systems with differential pressure sensors should be installed to maintain +2.5 Pa pressure gradients. Alarm systems can notify staff of pressure deviations for immediate rectification.

3. Optimising Air Changes Per Hour (ACH)

Maintaining 20–30 ACH ensures rapid dilution of contaminants. Computational Fluid Dynamics (CFD) modeling can assist in designing airflow systems to achieve uniform air distribution with minimal turbulence.

4. Zoning and Barrier Techniques

Designing clear zones—sterile core, semi-sterile periphery, and contaminated zones—with airlocks and controlled access points helps maintain airflow integrity and prevent cross-contamination.

5. Routine Maintenance and Validation

• Quarterly Inspections: Include airflow visualisation and particle count assessments.
• Annual Deep Cleaning: Involves HVAC duct cleaning, filter replacement, and recalibration of airflow systems.
• Continuous Monitoring: Automated systems track temperature, humidity, and pressure parameters in real-time.

6. Personnel Training and Behavioral Protocols

Training staff on best practices—limiting door openings, proper gowning, and minimising equipment clutter—reduces airborne particle generation.

7. Incorporating Advanced Technologies

• Ultraviolet Germicidal Irradiation (UVGI): Destroys airborne pathogens when integrated into HVAC systems.
• Filters with Antimicrobial Capabilities: Maintain sterile air quality in operating theatres by reducing the presence of airborne microorganisms that could lead to infections.

Final Thoughts

Effective airflow management in operating theatres is fundamental to infection prevention, regulatory compliance, and operational efficiency. By implementing advanced filtration systems, maintaining optimal air pressure gradients, and adopting modern HVAC technologies, healthcare facilities can significantly reduce the risk of airborne contamination. Continuous monitoring, regular maintenance, and staff training further reinforce a facility’s commitment to delivering safe and high-quality surgical care.