Surgical theatre suppression: why and how?
Overpressure in the operating theatre is based on a simple principle: air must always flow from the cleanest zone towards the less controlled zones. Practically, to achieve this objective, the operating room must be maintained at a slightly higher pressure than that of the adjacent rooms. This difference prevents outside air, which is often more heavily laden with particles or micro-organisms, from entering the theatre.
The issue is therefore directly linked to the prevention of surgical site or sensitive area infections. Even though contamination has multiple origins, controlling the aeraulic environment remains a recognised lever that must be a high priority. The mechanism is simple: the air transports particles that are potentially vectors for bacteria. It is therefore a matter of limiting their intrusion to make the surgical procedure safer.
Overpressure must also be seen as an element of overall balance. It replaces neither filtration nor air renewal, but reinforces their efficiency. Without this pressure differential, even perfectly filtered air can be disturbed by uncontrolled inputs.
How is overpressure implemented?
Overpressure is achieved by blowing in more air than is extracted. This imbalance creates an air “leak” towards the outside, generally through gaps or when doors are opened. It is precisely this outgoing flow that protects the room.
Everything therefore relies on the correct sizing of the flow rates. An efficient air treatment installation must provide a sufficient supply air flow rate, whilst maintaining a slightly lower extraction rate. This adjustment is tricky because too much overpressure can disrupt doors or comfort, and too little renders it ineffective.
System stability also depends on factors that are often underestimated. For example, a poorly adjusted door, an unsealed service penetration or frequent openings can compromise this pressure differential. This is why operating theatres frequently incorporate airlocks, which act as buffer zones.
Regulation is ensured continuously by differential pressure sensors. They make it possible to adjust flow rates and detect issues.
What references and what requirements?
Overpressure falls within a precise regulatory framework. In France, the NF S 90-351 standard structures the requirements applicable to operating theatres, particularly regarding cleanliness classes and the pressure cascade. Internationally, ISO 14644-1 defines particulate contamination levels, while EN 1886 governs the performance of air handling units.
Beyond the texts, performance relies primarily on overall consistency. A well-adjusted overpressure that is poorly utilised quickly loses its appeal. Conversely, a design that incorporates actual usage staff movement, door opening frequency, maintenance allows conditions to be stabilised over the long term.
