A negative pressure room, formally known as an Airborne Infection Isolation Room (AIIR), is a specialized patient environment used predominantly in healthcare facilities. The fundamental purpose of this room type is to contain airborne contaminants, such as viruses and bacteria, within a sealed space. This containment is achieved by carefully controlling the air pressure inside the room, making it slightly lower than the pressure in the adjacent hallway or corridor. By maintaining this differential, the room acts as a physical barrier, preventing infectious particles from escaping and circulating throughout the rest of the facility. This engineering control is a foundational component of infection prevention for diseases spread by the airborne route.
Understanding Air Pressure Differentials
The principle behind a negative pressure room relies on the physics of airflow, where air naturally moves from an area of higher pressure to an area of lower pressure. To create the necessary conditions, the room’s ventilation system is engineered to constantly exhaust more air than it supplies. This imbalance of airflow volume effectively lowers the atmospheric pressure inside the room relative to the outside environment, creating a slight vacuum effect. The required pressure differential is typically a small, precise measurement, often maintained at a minimum of 0.01 inches of water column.
This pressure differential ensures that any air exchange, such as when the room door is opened, results in air being drawn into the room from the corridor. Contaminated air is therefore trapped inside, unable to flow out to the surrounding areas where it could pose a risk to staff or other patients. To sustain this containment, the room must have a high air exchange rate, typically requiring a minimum of 6 to 12 air changes per hour (ACH).
Before the exhausted air is released back into the atmosphere outside the building, it is passed through a dedicated filtration system. This system frequently incorporates a High-Efficiency Particulate Air (HEPA) filter, which is designed to remove at least 99.97% of airborne particles that are 0.3 micrometers in diameter. This high-level filtration ensures that any captured infectious aerosols are neutralized, preventing environmental contamination as the air leaves the facility. Some designs also include a small transitional space called an anteroom, which helps stabilize the pressure gradient when personnel enter or exit the main isolation space.
Critical Applications in Infection Control
The primary application for negative pressure rooms is the isolation of patients with confirmed or suspected airborne infectious diseases. These rooms are designed to control and contain pathogens that can remain suspended in the air for extended periods, traveling over distances on air currents. By containing the source of the infectious agent, the room acts as a protective shield for the hospital environment.
Specific pathogens that necessitate the use of an AIIR include:
- Mycobacterium tuberculosis (TB), which is easily spread via aerosolized particles.
- Highly contagious viral illnesses like Measles (Rubeola) and Varicella (Chickenpox).
- Severe Acute Respiratory Syndrome (SARS-CoV).
- Middle East Respiratory Syndrome (MERS-CoV).
- The virus responsible for COVID-19, particularly when aerosol-generating procedures are performed.
The contained environment serves a dual purpose: protecting non-infected patients and safeguarding the healthcare personnel who must interact with the infected individual. The controlled inward airflow minimizes the chance of infectious aerosols reaching the corridor, where they could be inhaled by others. This focus on source control is a foundational element of hospital infection prevention protocols.
The requirement for an AIIR is determined by the specific mode of transmission of the disease, not simply the severity of the illness. For diseases spread primarily by contact or large droplets that fall quickly, a standard isolation room may suffice. The decision to use a negative pressure room is an administrative control measure, ensuring environmental factors are precisely managed to minimize the risk of airborne transmission to the wider patient population and staff.
Verification and Operational Safety Checks
Maintaining the required negative pressure relies on routine monitoring and verification checks. Digital pressure gauges, often mounted just outside the room, provide a constant, real-time reading of the pressure differential between the isolation room and the corridor. These electronic monitors are frequently equipped with audible and visual alarms to alert staff immediately if the pressure drops below the acceptable threshold, indicating a loss of containment.
In addition to continuous electronic monitoring, simple verification methods are used to visually confirm the direction of airflow. The “smoke test” involves releasing a small amount of non-toxic smoke near the bottom of the door. If the room is correctly pressurized, the smoke is visibly pulled under the door and into the room, confirming the inward flow of air. A similar check can be performed using a strip of tissue paper held near the door gap, which should be drawn inward if the system is functioning properly.
Operational safety is dependent on user adherence to protocol, particularly keeping the door to the negative pressure room closed at all times. Every time the door is opened, the pressure differential is temporarily compromised. Minimizing the duration of this breach is necessary to maintain the integrity of the containment. Staff are trained to keep patient traffic and unnecessary entry to the room to a minimum, ensuring the ventilation system can consistently maintain the balance required for safe operation.