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It is vital to maintain and control air flow within operating theatres
It is vital to maintain and control air flow within operating theatres
Controlling airborne contamination within operating theatres

We speak to Mike Hodges of Apreco about how well-considered ventilation systems can optimise the mitigation of airborne contamination within operating theatres 

The control and prevention of nosocomial infections, also known as hospital-acquired infections (HAIs) or healthcare-acquired infections (HCAIs), is paramount in any healthcare facility. 

And, while significant progress has been made; the BMJ reports that an estimated 4.7% of all adult inpatients acquired an HCAI across all general and teaching hospitals in England in 2016/2017, costing the NHS £2.1billion.

HCAIs result in lengthier hospital stays, the need for remedial surgery, staff absences, and added stress on the patient and their family members. 

These infections also account for 5.6 million occupied hospital beds, 62,500 healthcare provider absences, and 22,800 patient deaths, with an estimated 3.5% of patients who acquire an HCAI dying from this infection. 

Surgical Site Infections (SSIs) are one of the most-common types of HCAI, accounting for 15.7% of all reported cases. 

These cause numerous post-surgical morbidities and are major contributors to post-surgical mortality rates. 

A financial burden

Surveillance data submitted by 195 NHS hospitals in 2019/2020 reports that 5% of all surgical patients are likely to develop an SSI, with 16% leading to post-surgical morbidities. 

Surgical incisions expose our systems to these infections, which are caused by bacteria present on the skin itself which spreads to the incision site; an infection present in the body which spreads during surgery, whether it be from a specific area or organ; or from contaminants in the environment, such as the air or unsterile surgical instruments.

Air flows away from the operating theatre to the corridor
Air flows away from the operating theatre to the corridor

These infections significantly increase the clinical and financial burdens on healthcare systems. 

The NHS reported that infections associated with hip and knee replacements are as high as 4%. 

And an estimated £300m could be saved per year if hospitals decreased this rate to 1%. 

The link between SSIs and air quality within the operating theatre is well established. 

These statistics alone underpin the importance of mitigating airborne contamination within these environments. 

Airborne microbes are just as present in healthcare environments as in any other setting.

Invisible particles fill the air around us and these can be anything from liquid droplets to smoke and soot. 

A colony-forming unit (CFU) is an airborne particle laden with bacteria or other disease-causing microbes. 

A breeding ground

A microbe or pathogen-carrying particle can enter the human body through various means, such as the COVID-19 virus that enters the body via the respiratory system. 

Within the NHS, respiratory tract infections account for 22.8% of all HCAIs.

Equipment, surfaces, surgical incision sites and the respiratory tract can all become contaminated with dust, lint, the patient’s microbial flora present on the skin, and respiratory droplets present in the air. The use of lasers to cauterise wounds also pollutes the air with smoke, gas, and molecular contaminants, which pose further risks to infection.

Managing the amount and flow of airborne contaminants in an operating room environment is therefore a critical line of defence in mitigating the risks of infection. 

Operating theatres use specialised ventilation systems to prevent the ingress of airborne microbes into rooms. 

The Health Care Act 2009 places a duty of care on healthcare providers to ensure these systems operate correctly and efficiently, noting that increased health risks will occur if ventilation systems do not meet required standards.

And any failure of the specialised ventilation system may expose healthcare professionals and patients to unacceptable levels of contamination. 

It is therefore crucial that the management of an operating theatre’s specialised ventilation system is regularly reviewed as this can make a significant impact on controlling, and preventing, SSIs.

Best-practice approaches 

Over the years, the ventilation requirements of the operating theatre have changed to accommodate increasingly-complex surgeries. 

The Health Technical Memorandum 03-01 (HTM), updated on 22 June 2021, is a well-established guidance document used for the design and maintenance of specialised ventilation within acute healthcare environments. 

This relates specifically to environments that require close control, where patients may be particularly susceptible to airborne infection.

It is important to note that the latest HTM has been reviewed against the known transmission of the severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2), where ventilation is one of the key components in infection control. 

Any departures from the HTM should provide a degree of safety no less than that which can be achieved by following the HTM guidance.

The document provides comprehensive advice specifically for estates and facilities managers, senior healthcare management, as well as specifiers, suppliers, designers, and installers.

Ventilation is used extensively throughout all types of healthcare premises to provide a safe and comfortable environment for patients and staff. 

The HTM 03-01 recommends making provisions for more-specialised ventilation in areas such as operating departments, critical care facilities, isolation rooms, and primary treatment areas to help reduce airborne infection risks. 

It details the four main functions of the supply of air to the operating theatre as follows:

  • To dilute the airborne microbial contamination within the operating theatre which occurs due to surgical activity and microbiological material shed by the staff
  • To dilute and aid in the removal of waste anaesthetic agents and odours
  • To prevent airborne contaminants from entering the operating theatre from less clean areas through control of the air movement
  • To control the temperature of the environment and if necessary, control the humidity
The air pressure stabiliser closes to protect the cleanliness of the OR and prep room
The air pressure stabiliser closes to protect the cleanliness of the OR and prep room
Air pressure stabilisers lead air to flow from the OR to the corridor
Air pressure stabilisers lead air to flow from the OR to the corridor

These guidelines also prescribe routine testing to evaluate the efficacy of existing healthcare ventilation systems, irrespective of the age of installation. 

Applicable to new and existing healthcare buildings, the ventilation requirements are for use at various stages of the whole building lifecycle and state that it is essential for them to be inspected annually. 

It is also crucial that the layout of an operating department incorporates cascade ventilation systems and air pressure stabilisers to comply with these health technical regulations.

There are four routes by which airborne contamination may enter the operating theatre:

  • When they are shed directly by the room occupants
  • As a result of the work activities carried out by staff
  • When transferred from an adjacent space
  • Through the air supplied to the room

To reduce the risk of infection and maintain theatre cleanliness, hospitals around the globe employ cascade ventilation systems that work in tandem with air pressure stabilisers.

Mike Hodges
Mike Hodges
Air pressure is highest in the prep room, forcing air to flow from the prep to the OR
Air pressure is highest in the prep room, forcing air to flow from the prep to the OR

These specialised ventilation systems facilitate a unidirectional flow of air throughout the operating department.

Studies claim that these unidirectional airflow systems control and limit colony-forming units or contaminated air. 

This system cascades airflow through the various rooms, from the sterile area, through various tiers, and finally into the designated unsterile area. 

Mitigating the risk

This helps prevent contaminated air from being continuously circulated in the room and mitigates the ingress of airborne microbes. 

Globally, these ventilation systems are used in areas such as isolation rooms, operating theatre suites, aseptic suites, pharmacies, and sterile working environments.

But they cannot work effectively without the use of air pressure stabilisers to regulate the air pressure differentials between adjoining rooms. 

Regulating in this way establishes an invisible barrier that prevents air from one area entering that of the adjoining area whenever doors or other ingress or exit points are opened.

When doors or exit points are opened within the operating theatre, the air pressure will drop. And this will trigger the counterbalanced blades of the air pressure stabilisers to close, forcing air to be directed through the doorway. 

This is known as ‘door-flow protection’ and the action prevents unwanted particles from passing into the clean environment. 

Managing the amount and flow of airborne contaminants in an operating room environment is a critical line of defence in mitigating the risks of infection

As the flow of air is constantly maintained, unwanted particles will move down through the operating department, away from the patients and staff.

There are two methods of door-flow protection that are utilised to mitigate the risks of contamination of a clean area from less-clean areas:

  • The closed-door protection method creates a pressure differential across a closed door, directing any air leakage from a clean to less clean area via air pressure stabilisers at a set pressure as defined in the HTM 03-01
  • The open-door protection method results in air being diverted from the air pressure stabiliser which closes when an adjacent door opens, this air passes a minimum volume as stated in HTM 03-01 through the open doorway from a clean to less clean area

It is important to note that failure to provide devices such as air pressure stabilisers will result in uncontrolled airflows when personnel move throughout the rooms. 

Air pressure stabilisers are critical in the control of air between areas of the department. 

As per the HTM 03-01, the specialised ventilation system and layout of air pressure stabilisers are intended to:

  • Protect sterile packs and instruments from pre-contamination within the preparation room
  • Remove airborne contaminants from the operating theatre and prevent the ingress of airborne contaminants from adjacent areas
  • Protect staff from casual exposure to anaesthetic agents within anaesthetic rooms
  • Remove aerosolised microbiological contamination from the Scrub – these are released when staff scrub up

To meet these requirements, the layout of air pressure stabilisers within a conventional operating department should facilitate the following:

  • Air should flow from cleaner areas to less-clean areas
  • The anaesthetic room will be at an intermediate pressure between the operating theatre and the corridor
  • Whether the scrub is a separate room or a bay within the operating theatre, there should be a pressure stabiliser that discharges onto a corridor
  • The utility room maintains a negative pressure with respect to the operating theatre to prevent contaminants in the surgical waste from re-entering the theatre
  • Air cascading from the operating suite should be removed in the adjacent corridors
  • The sterile pack store should be at a positive pressure to the corridor

The layout of air pressure stabilisers and pressure differential requirements will differ if the operating suite is intended for surgery on infectious patients. 

For this, a dedicated neutral-pressure theatre, or a conventional theatre that can be easily converted into a neutral-pressure suite will allow for variations that can be referred to on page 61 on the HTM document. 

Any failure of specialised ventilation systems may expose healthcare professionals and patients to unacceptable levels of contamination

These variations prevent air from the interchange of air between the theatre and the corridor when the theatre exit door is open. 

When doors from the preparation room or anaesthetic are opened, air flows from them and into the theatre. 

It is also important to note that these guidelines specify the use of air pressure stabilisers of a balanced blade type, so that fine adjustments of the pressure setting can be made over a wide range of flow rates.

Clean and silent

They should also be made from materials that allow for cleaning and disinfection and be silent in operation.

Air pressure stabilisers, such as the APSX Air Pressure Stabiliser range by Apreco, are fully adjustable with an operating range of 3 to 50Pa and a setting accuracy of +/- 1Pa over the operating range.

The APSX Air Pressure Stabiliser has been purpose designed for the application of differential air pressure in environments such as operating theatres to control airborne contamination.

They effectively regulate differential air pressures between adjoining areas. 

And, once air pressure changes reach certain levels, the stabilisers close to maintain a clean room and sterile operating theatre environment. 

The air pressure stabiliser:

  • Operates within a comprehensive range of 3 to 50pa
  • Is manufactured in the UK according to the highest quality control standards
  • Is approved and certified with serial number traceability

Apreco’s APSX Air Pressure Stabiliser and associated products are also supplied as standard with SteriTouch paint finish, utilising silver technology – which is already used extensively within the healthcare sector as excellent anti-microbial protection in conjunction with good hygiene practices. 

SteriTouch is extremely effective in helping to protect against harmful bacteria including MRSA, Ecoli, salmonella and C-diff. 

It is crucial that the layout of an operating department incorporates cascade ventilation systems and air pressure stabilisers to comply with health technical regulations

And the coating also allows for easy cleaning of the blades and frame, with removable blades further simplifying adjustment, cleaning and maintenance requirements.

Air pressure control within hospital operating theatres is a first-line defence and a vital measure in mitigating airborne contamination. These systems ultimately save lives, lessen the burden on healthcare systems, and help to manage healthcare budgets.

Annual verification

The HTM 03-01 advises that annual air pressure testing be undertaken to verify the operating theatres meet the standards to be deemed fit for purpose. 

It is also advised that annual verification reports be carried out to ensure air pressure stabilisers are still working as per the original design.

It is the responsibility of management to ensure that regular inspection and maintenance of ventilation systems and air pressure stabilisers are carried out periodically. 

And records of the ventilation performance, including the date of annual inspection, must be kept as a legal requirement.

In addition, air pressure stabilisers should:

  • Not be obstructed and should be checked for silent operation
  • Blade pivots cleaned, and blade stops inspected and replaced as required 
  • Be checked for correct operation at the set opening pressure
  • Be cleaned as necessary

The correct operation of air pressure stabilisers is critical to the performance of operating theatres. 

A malfunctioning system not only causes costly disruption and unplanned downtime, but it could also impact patient and staff safety. 

Apreco carries out condition reports and site surveys on air pressure stabilisers to ensure that operating theatres remain fully compliant. 

Air pressure control within hospital operating theatres is a first-line defence and a vital measure in mitigating airborne contamination

Recent projects include the refurbishment of units at Russell’s Hall Hospital and the survey of the catheterisation laboratories and operating theatres at Royal Papworth Hospital, Cambridge.

Apreco also offers a wide range of replacement parts for any damage occurred. 

Check and check again

The mos- common instances for refurbishment occur due to yoke breakages or bent blades caused by improper cleaning of the units. 

Air control blades are free of surface-mounted balance weights and can be easily wiped clean for sterilisation. 

But care should be taken not to bend the air control blade in any way as this will affect its balance and the pressure setting.

The blade can remain in its frame for weekly cleaning with an option to fully remove if desired. 

These blades should be checked for correct fitment into the yokes of the flane following the cleaning process. 

And mops should not be used to clean the blades as this can damage the blades and yokes.



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