How to reduce the risk of post-operative surgical site infection (SSI) rates through regular inspections


Research has indicated that the level of post-operative infection and the rate of surgical wound infections is strongly influenced by operating theatre suitability and quality, thus, the level of airborne bacteria within an Operating Theatre is directly proportional to infection rates. A safe and stable operating theatre is an environment in which all sources of pollution and any micro-environmental contaminates are kept under strict control. This can be achieved only through careful planning, on-going maintenance and periodic checks as well as proper training for staff.


A surgical site is the incision made by a surgeon to carry out a given surgical procedure, and the tissue handled or manipulated during the procedure. A surgical site infection (SSI) occurs when micro-organisms get into an area that has been operated on and multiply in the tissues. With an already struggling system for free bed spaces within hospitals, minimising SSIs is vitally important to help reduce all hospital-acquired infections and therefore reducing post-operative days in hospital. The cumulative SSI incidence remains low for orthopaedic surgery prosthesis at less than 1%, which demonstrates the importance of Ultra Clean Ventilation (UCV) theatres and their effectiveness when used appropriately. The laminar air flow from a UCV canopy can create up to 450-500 air changes per hour, which dramatically reduces any chance of micro-organisms contaminating the surgical wound during surgery.

Within the healthcare industry, an Operating Theatre is classed as a critical ventilation system, which is defined within HTM 03-01 Part B as, ‘…the loss of service from such a system which would seriously degrade the ability of the premises to deliver optimal healthcare.’ HTM 03-01 requires that all critical ventilation systems are inspected quarterly and that their performance be measured and verified annually. An annual verification must be undertaken, not only to be compliant with current industry regulations, but to also assist with the prevention of SSIs within the theatre suite. Both UCV and conventional operating theatres, treatment rooms used for all types of surgical procedures, obstetrics and maternity procedures all fall under this category.


Annual HTM Verification

An annual verification must be undertaken in accordance with HTM 03-01 for all theatre suites designed since 2007 (theatre suites designed prior to 2007, when the HTM 03-01 regulations came into force, may still adhere to its predecessor HTM 2025 for performance). These annual verifications are a way of monitoring the performance of an operating theatre, ensuring the system is still achieving the expected standards specific to the application, it’s operating to an acceptable performance level and is fit for purpose. The growing presence of the Care Quality Commission’s (CQC) inspections are ensuring every theatre suite has an annual verification and any rectification works, such as HEPA filter changes or rebalancing of the theatre suite, are completed immediately.

The below testing procedures indicate what is required as part of an annual HTM 03-01 operating theatre verification:

  • Full measure of the supply and extract airflow rates
  • Measurement of room pressure differentials
  • Measurement of room noise levels
  • Record room temperature and humidity
  • Air quality checks using particle counter
  • Check of control functions
  • Measure airflow velocities under UCV canopy (UCV theatres only)
  • AHU inspection
  • Produce detailed report outlining performance results, incl. additional information such as schematic diagram of the theatre layout and supply AHU


Additional testing procedures, which are not required as part of an annual HTM 03-01 verification, but often included or undertaken following remedial works in a UCV theatre are:

  • Pre-filter replacement
  • In-situ integrity testing of HEPA filters
  • Entrainment testing

Microbiological Air Sampling

Provided an annual verification is undertaken and the specialised ventilation system is performing as it should be, microbiological air sampling does not need to be undertaken on a routine basis. However, during the commissioning of a new operating theatre or following any substantial modifications to an existing theatre, which may impact the airflow patterns within the theatre, microbiological sampling should be done to determine the quality of the air and levels of microbial airborne contaminants; this may include alterations to the ductwork or fabric of the theatre, but does not include routine remedial works such as filter changes. Microbiological air sampling is useful and often used during investigations in to why a theatre has a high infection rate. However, many hospitals choose to have microbiological air sampling done as part of their annual verification to closely monitor airborne contaminants and ensure the quality of air within the theatre suite, therefore helping with the reduction of post-operative SSIs.

It is important that prior to any microbiological air sampling the theatre suite has been sufficiently cleaned and decontaminated if necessary. The specialised ventilation system serving the operating theatre should have achieved a steady state condition and been left empty for 15 minutes before remotely activating the sampling equipment. Aerobic cultures on non-selective media should not exceed 10 bacterial and/or fungal colony forming units per cubic metre (<10 CFM/m³).

Both annual verification and sampling works within the operating theatre should be undertaken by trained, experienced and qualified engineers. Crowthorne Group have been working in operating theatres and cleanrooms for many years and understand the importance of accuracy and consistency when providing these services within such critical environments.


For more information or assistance with routine inspection and verification of your theatre suites please contact Crowthorne Group on

+44 (0)1252 372333/ for the UK or +353 (0)1824 3670/ for our Irish division, BPS Crowthorne.