Monitor Pressure in Isolation Hospital Rooms
What is an Isolation Room
Isolation Room/Ward is a patient room where the air inside the room is sucked up creating a negative pressure in the room that ensures that the air is flow is from out the isolation room to inside but not from inside to out thus preventing the number of airborne infectious particles is reduced to a level ensuring the cross-infection of other people within a healthcare facility is highly unlikely.
Factors to achieve Isolation:
- Control of the quantity and quality of intake or exhaust air.
- Maintain different air pressures between adjacent areas.
- Designing airflow patterns for specific clinical procedures.
- Diluting infectious particles with large air volumes.
- Air filtration – HEPA filters, etc.
Types of Isolation facilities:
Neutral or standard room air pressure: for example, standard air conditioning, also known as Class S
Positive room air pressure: This is generally used where an immune-compromised patient is protected from the airborne transmission of any infection, Class P
Negative room air pressure, This is generally used where others are protected from any airborne transmission from a patient who may be an infection risk, Class N
Negative room air pressure with additional barriers including an Anteroom, also known as Class Q for quarantine isolation.
Recommended Pressure Gradients :
An isolation room where Anteroom is not provided, the recommended minimum differential pressure between the isolation room and adjacent spaces should be 15 Pa(0.06 In WC). If however an anteroom is provided, the recommended minimum differential pressure between the isolation room and ambient pressure should be 30 Pa. Any additional pressure gradients between successive pressurized areas should not be less than 15 Pa.
Why is Isolation room important
Controlling the spread of airborne infectious diseases in health care facilities is a serious concern to patients, staff, and visitors. To minimize the spread of airborne infections, certain rooms within a hospital are designed as airborne infectious isolation (AII) rooms with negative-pressure differential or protective environment (PE) rooms with a positive-pressure differential.
General requirements of an Isolation room
- One patient bed
- Separate toilet room with a hand-washing sink.
- Well-sealed to prevent excess air leakage into or out of the room
The latest edition of the American Society of Heating, Refrigerating and Air-Conditioning Engineers' (ASHRAE's) Standard 170, states that each isolation room should have a permanently installed visual device or mechanism to constantly monitor the air pressure differential of the room when occupied by a patient who requires isolation.
Most of the electronic monitors consist of two main components: a wall-mounted control panel and a sensor. The control panel usually is mounted on a corridor wall adjacent to the entrance of the isolation room and generally displays the pressure difference in inches of water column (WC) or Pa (Pascals).
(Wall Mounted Image)
Not only providing a continuous display of pressure differential, but the control panel should also include both audible and visual alarms to warn staff when room pressurization is violated. The alarm should sound when the measured room pressurization is below the alarm setpoint. For example, in a room designed to maintain a pressure differential of minus 0.03-inch WC, the alarm could be programmed to activate when the pressure differential falls to minus 0.01-inch WC)
(Audio Visual Alarm Image)
Exhaust System
For the exhaust system serving AII(Airborne Infection Isolation) rooms, the exhaust fan should be located outdoors, if possible, and be placed as far away from intakes and public areas as practical, but no less than 25 feet with discharge above the roof. For outdoor fans, all exhaust from AII rooms should be exhausted by means of a vertical exhaust stack or exhaust fan with a vertical discharge arrangement.
When an anteroom (a small outer room that leads to another room and that is often used as a waiting room) is provided, airflow should be from the corridor into the anteroom, and from the anteroom into the patient isolation room. To maintain the required pressure differential, the exhaust air quantity must always be higher than the supply airflow. Depending on such factors as room size and the room’s heating and cooling loads, more than 12 air changes per hour may be necessary. Typically, a minimum airflow difference of 150 to 200 cubic feet per minute (CFM) is adequate to maintain a pressure differential in a well-sealed room.
Combination of AII/PE rooms. In the past, some isolation rooms were designed to be switchable between negative and positive isolation; however, this type of isolation room is no longer allowed. To address the need to protect an immunocompromised patient with a known infectious disease, ASHRAE 170 now includes guidelines for a combination of AII/PE room. Unlike separate AII and PE isolation rooms, the combination isolation room must be used with an anteroom.
Supply air for the room must be located in the ceiling above the patient bed, with return air taken from the ceiling near the patient room door similar to a standard PE isolation room. The pressure relationship for the anteroom shall either be positive in relation to the AII/PE room and corridor or negative in relation to the AII/PE room and corridor.
In addition, ASHRAE 170 requires two separate permanently installed visual devices or mechanisms to constantly monitor the air pressure differential. One device monitors the pressure relationship between the anteroom and AII/PE room and the second checks the pressure relationship between the anteroom and corridor. The exhaust from the combination AII/PE room, associated anteroom, and associated toilet room must be discharged directly to the outdoors without mixing with exhaust from any non-AII rooms.
Isolation Room maintenance:
After construction is completed, but prior to occupancy, the mechanical or balancing contractor typically will adjust the airflow quantities as directed by the design engineer to ensure that the isolation room is operating as designed. In addition, isolation rooms should be commissioned to prove correct pressure relationships, proper operation of room controls and the functionality of the pressure monitor and alarms. ASHRAE 170 also requires that the room be tested daily while it is being used as an isolation room.
The room pressure should be checked monthly with a smoke trail or similar testing. Most manufacturers of pressure monitors also recommend that the pressure monitor be recalibrated annually. The results of this periodic testing should be recorded because the authority having jurisdiction may request the data during a survey.
In addition to routine testing of the isolation room, the hospital staff who will be utilizing or maintaining the room should be trained on the proper use of the room, including how the pressure monitor works. A benefit of using a continuous pressure monitor connected to the building automation system is that the pressure differential for the isolation room can be monitored, trended and reviewed. It also can be used to alert hospital staff if the room is not performing as designed.
