Negative pressure rooms, also called isolation rooms, are used in hospitals to isolate patients with infectious diseases from others. They work by maintaining a lower air pressure inside the room so that contaminated air does not flow out when the door is opened. Several methods are used to control airflow and filter exhaust air before it leaves the room. There are four main types of isolation rooms - Class S rooms with neutral pressure, Class P positive pressure rooms, Class N negative pressure rooms that protect those outside, and high-security Class Q rooms with additional safeguards like anterooms. Room pressure can be tested simply with smoke or tissue, but electronic monitors offer continuous monitoring at a higher cost.

1. Negative Pressure Rooms
By
Dr Hatem Elbitar
What are Negative Pressure Rooms?
Negative pressure rooms, also called isolation rooms, are a type of hospital room that
keeps patients with infectious illnesses, or patients who are susceptible to infections
from others, away from other patients, visitors, and healthcare staff.

2. Image Credit: Chokniti Khongchum/Shutterstock.com
They are a common method of infection control and are used to isolate patients with
contagious, airborne diseases such as measles, tuberculosis, SARS, MERS, and
COVID-19.
How do negative pressure rooms ork?
They are called negative pressure rooms because the air pressure inside the room is
lower than the air pressure outside the room. This means that when the door is opened,
potentially contaminated air or other dangerous particles from inside the room will not
flow outside into non-contaminated areas.
Instead, non-contaminated filtered air will flow into the negative pressure room.
Contaminated air is sucked out of the room with exhaust systems, which are built with
filters that clean the air before it is pumped outside of and away from the healthcare
facility.
There are several ways that airflow within a room can be controlled.
These methods include:
 Controlling the quantity and quality of the air being put into and out of a room
 Controlling the air pressure between adjacent rooms or areas
 Designing specific airflow patterns for certain clinical situations or procedures
 Diluting infectious air or particles with large amounts of clean air
 Filtering the air with HEPA filters, among other types.
Some negative pressure rooms require an anteroom, which is an airlock room that
provides a safe area for healthcare professionals to change into or out of protective
clothing, transfer or prepare equipment and supplies, and can protect other rooms from
contamination if pressure is lost within the negative pressure room.

3. The temperature and humidity in a negative pressure room must be monitored as the
increased amount of air exchange within the room can create draughts that may be
uncomfortable for a patient.
Negative pressure rooms do not have to be individual rooms for a single patient at a
time. Common negative pressure environments in hospitals can include waiting areas,
bathrooms, and triage areas, where infections can easily be spread.
The Different Types of Isolation Rooms
There are four types of isolation rooms, two of which are negative pressure rooms.
Class S
Class S isolation rooms are neutral or standard air pressure rooms, in which normal air
conditioning is used. They are used for contact isolation, which is a type of infection
control requiring the use of gloves, gowns, and masks to ensure no one comes into
direct contact with a patient with an infectious illness. Class S rooms can be used for
other means when not in use for patients needing isolation.
Class P
Class P rooms are positive pressure rooms. Patients who are immunocompromised are
protected from becoming infected by potentially dangerous particles from other patients,
visitors, or healthcare staff.
Class N
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Class N rooms are negative pressure rooms in which people outside of the room are
protected from any infectious airborne particles inside the room. Class N rooms should

4. be at the front of an inpatient unit so any patients going into the room do not pass by
other patients in different areas of the unit.
Class N rooms are equipped with an exhaust system that removes more air than the
room is being supplied with. Anterooms are not always necessary for Class N rooms.
Class Q
Class Q rooms are negative pressure rooms that include additional infection control
measures such as an anteroom and are used in situations requiring quarantine.
There are higher precautions taken with Class Q rooms, including alarms to alert staff to
loss of pressure within the room, self-closing doors, a separate bathroom for the patient,
and a ventilation system that does not allow any exhausted air to return into the room.
HEPA filters should be used for the exhaust air to control contaminated air entering the
environment outside of the healthcare facility, and communication systems can be used
to help staff to safely coordinate movements inside and outside of the room.
There are also Class A pressure rooms, but they are no longer built into new healthcare
facilities and are not recommended for use in existing facilities. Class A rooms are
alternating pressure rooms that can be used as either negative or positive pressure
rooms. However, this increases the risk of human error when setting the airflow for the
room, which can cause very serious complications for infection control.
How can room pressure be tested and monitored?
Although there are guidelines from the Centers for Disease Control and Prevention on
how to properly monitor and maintain infection control in healthcare facilities, there are
no set guidelines on how to monitor acute negative pressure rooms.
To test the pressure inside an acute negative pressure room, a smoke or tissue test can
be performed.

5. To carry out these tests, a smoke capsule or tissue is placed at the bottom of the
negative pressure room door. If the smoke or tissue is pulled underneath the door, the
room can be seen to be negatively pressurized.
Although this is a simple and cost-effective test, it does not provide continuous
monitoring of negative pressure rooms. It also does not show if a room is over or under-
pressurized, only that the room is negatively pressurized to some degree.
Electronic monitors placed in the isolation room and the areas outside of the room do
offer continuous monitoring of the room pressure. They are equipped with an alarm that
will sound if the room becomes incorrectly pressurized.
However, a risk with electronic monitors is that they can become contaminated and
provide false readings. Additionally, they are costly and healthcare staff have to be
trained to use them.