Ventilation system
Goals
- Comfort of patient and staff
- Removal of pollutants/aerosols
- Temperature and humidity control
- Control air movement to minimize the transfer of airborne contaminants from less clean to clean areas.
- Airborne contaminants may enter an operating room via the following routes:
- Through the supply air;
- Shed by operating staff
- Together with sheding by patient's own skin, most common cause of wound infection
- Through surgical activities
- Transferred from adjacent spaces.
2 types of system
- Recirculating system
- Is one that recirculates some or all of the inside air back to the OR suites or some other part of hospital,
- When a recirculating system is used, the air return duct should have a high efficiency particulate air (HEPA) filter built into the system.
- In an OR where inhalational anesthetics are used, there should be separate systems for ventilation, vacuum (patient and surgical suction), and waste anesthetic gas disposal.
- Non-recirculating system
- All air brought to the room is conditioned, outside air.
Room ventilation affects the distribution of airborne particles in four ways:
- Total ventilation (dilution)
- As the air flows of the room increases, the greater the dilutional effect on airborne particles. However, resultant turbulent flow also increases microbial distribution throughout the room.
- Air distribution (directional airflow)
- Laminar flow:
- Low-velocity unidirectional flow
- Minimizes the spread of microbes in the room.
- This is described as an entire body of air within a designated space (theatre suite) moving with uniform velocity in a single direction along parallel flow lines.
- True laminar flow is only achieved when approximately 100% HEPA filter coverage occurs.
- Laminar flow ventilation comprises a continuous flow of air with bacteria less than 10 colony-forming units/m3.
- Despite this, infection rates for joint replacement surgery have actually been show to increase in laminar flow versus conventional theatre ventilation (reasons remain unclear).
- Room pressurization (infiltration barrier)
- Negative pressure:
- Direction of flow: outside → OR
- Used for highly infective rooms in the hospital (e.g. isolation rooms for tuberculosis patients)
- Positive pressure:
- Direction of flow: OR → outside
- Used for protective environments (e.g. ORs and rooms with immunocompromised patients).
- Filtration (contaminant removal)
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