Table 2 Differences between positive and negative pressure rooms
From: Heating, ventilation and air conditioning (HVAC) in intensive care unit
Characteristic | Positive pressure system | Negative pressure system or airborne infection isolation room (AIIR) |
|---|---|---|
Purpose | To create a protective environment to the patient to avoid acquiring any airborne infection (does not require an ante-room). | To create a protective environment to the healthcare providers as well as other patients in the ICU (requires an ante-room). |
Type of patients requiring isolation | Burns, post-transplant, febrile neutropenia (also for patients in operating rooms) | Tuberculosis, swine flu, COVID-19 and other airborne viral diseases |
Direction of airflow | Outside the room (away from the patients) | Inside the room (towards the patient) |
Pressure | More than 2.5 Pa preferably + 8 Pa (ideal) | Less than 2.5 Pa |
Supply air | More than the sum of return and exhaust air | Less than the sum of return and exhaust air |
Recirculation | 90–95% | 80–90% (if required) |
Air change per hour | > 20 | ≥ 12 |
Filtration efficiency | Supply: 99.97% at 0.3 μm DOP All supply air must pass through HEPA filters | Supply: 90% (dust spot test) All supply air to be exhausted without recirculation HEPA (99.97% at 0.3 μm DOP) must be used on the supply side if recirculation is used. HEPA is required on the exhaust side too, when exhausting air to the outside is not practical |