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Laminar Flow Theatres: An Overview

Sterility is non-negotiable in an operating theatre. Surgical site infections (SSIs) can be a life-threatening complication as OR Today reports that 2 in 100 surgeries in the United States of America result in SSIs.

Laminar flow systems, which have been in use and development for several decades, go a long way in controlling infections by reducing levels of airborne bacteria. In this article we provide a brief overview of the history, mechanisms and benefits of laminar flow theatres – a crucial but little-discussed part of medical technology.

History

In many countries, surgery carried a very high risk of post-operative infection right up to the 1950’s. Basic sterilization processes were used, such as using boiling water to sterilize surgical instruments and having extractor fans remove the steam. This created negative air pressure that would draw in air from the surrounding rooms – and with it, contaminants. After much trial and error, it was found that when they reversed the air flow, infections were drastically reduced.

After that, procedures became better understood and more hygienic, and from the mid-1960s laminar flow systems started being developed and becoming popular. They have since then evolved, including their progression from fibreglass wall packs to High Efficiency Particulate Air (HEPA) filtration systems with either ceiling-mounted vertical or wall-mounted horizontal airflow.

Benefits

Laminar flow theatres work to prevent airborne bacteria from getting into open wounds, as well as removing and reducing levels of bacteria on exposed surgical instruments, surgeons and the patient’s own skin. The systems ensure that there are less than 10 Colony Forming Units (CFUs) of bacteria per cubic metre of air in the room. By doing this, they prevent dangerous contamination.

Mechanism of Action

The way in which laminar flow theatres work is, very basically, to filter the air and create a powerful, calm and uniform unidirectional airflow. They rely on fans to create air velocity, which may be downward. There can be multiple laminar flow diffusers in a single operating theatre. Any turbulence can negate the bacterial reduction and removal effect of the system, so it is very important that operating theatre personnel move around carefully and deliberately.

Vertical laminar flow theatres consist of a laminar flow plenum, sometimes called a CALP “Complete Air Light Plenum” above the operating table through which HEPA filtered air is diffused uniformly over the patient and operating staff. This creates a sterile air zone around the patient. It is also important to validate by means of particle counts an operating theatre on a regular basis.

The laminar flow system’s HEPA filters remove bacteria, viruses and any dust particles from the air flowing in and out of the theatre, creating an isolated clean environment. In many countries, laminar flow systems must comply with ISO 14644 – the standard for regulation of cleanrooms and related environments, assuring high standards of sanitisation.

Final Observations

It is highly recommended that laminar flow systems be installed in operating theatres wherever possible – that is, wherever they can be afforded. They can be a significant financial outlay, but tend to last a number of decades – making it economical in the long run. Laminar flow systems can be switched over to function as conventional airflow systems – but the reverse cannot be achieved.

It is important to remember that laminar flow systems are most effective when combined with other infection control measures, such as body exhaust suits for surgery personnel, and a strict approach to pre and post-operative hygiene procedures. The systems should not be seen as the sum total of contamination prevention.

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