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Design of isolation rooms in hospitals
Dr(Lt Col) SKM Rao
 Transmission-based
infection control practices are central to preventing the transmission of microorganisms
within healthcare settings. The five main routes are contact, droplet, airborne,
common vehicle and vector-borne transmission. Sometimes more than one route
can transmit the same microorganism. Common vehicle and vector borne transmission
are discussed only briefly, because they are uncommonly associated with nosocomial
infections, and they are less affected by room design and construction factors.
Contact Transmission
Contact transmission is the most important and frequent mode of transmission
of nosocomial infections. It can be subdivided into direct-contact transmission
and indirect-contact transmission.
(a) Direct-contact transmission involves direct body surface-to-body surface
contact and physical transfer of micro-organisms from an infected or colonised
person to a susceptible host.
(b) Indirect-contact transmission involves the contamination of an inanimate
object (such as instruments or dressings) by an infected or colonised person.
Droplet Transmission
A person’s coughing, sneezing and talking generate droplets. Procedures
such as suctioning and bronchoscopy are also a source of droplets. Transmission
occurs when an infected or colonised person generates droplets containing microorganisms
which are propelled at a short distance through the air and deposited on the
conjunctivae, nasal mucosa or mouth of a host. Droplets do not remain suspended
in the air, so special air handling and ventilation are not required to prevent
droplet transmission. (Do not confuse droplet transmission with airborne transmission.)
Airborne Transmission
Airborne transmission occurs when either airborne droplet nuclei or dust particles
disseminate infectious agents.
Droplet nuclei
Droplets have large surface areas and therefore rapidly evaporate in the air.
Droplets rapidly evaporate in low relative humidity. The residue of the droplet
after evaporation, which contains any organism originally present, is called
a droplet nucleus. It is typically 5 µm or smaller in size. As the water
evaporates, the weight of the droplet decreases and thus the droplet-settling
rate decreases. Droplet nuclei settle so slowly that they remain airborne in
occupied spaces and circulate on air currents until mechanically removed by
the ventilation system.
The high velocity with which coughing and sneezing expel droplets from the respiratory
tract results in large numbers of bacteria or viruses entering the air in smaller
droplets than those produced by quiet breathing and speech. Relatively frequent
air changes are needed to remove infectious droplet nuclei from the air of a
room. Air currents can widely disperse such microorganisms, which a susceptible
host (near or quite far from the source patient) can then inhale. Control of
environmental factors (such as special air handling and ventilation) is necessary
to prevent nosocomial airborne transmission of microorganisms such as measles,
chicken pox and mycobacterium tuberculosis.
Dust
The control of dust-borne particles is often overlooked. Dust contaminated by
viable infectious agents may build up as a reservoir capable of causing an outbreak
of infection, even after the departure of the infectious patient from whom the
pathogens originated. Dust may become contaminated when dried sputum and other
infectious secretions suspended in the air as dust particles mix with environmental
dust.
Isolation rooms
Surveillance, based on clinical and/or microbiological criteria,
identifies patients who require isolation. Physical isolation is ceased when
the patient is no longer infectious. When possible, a patient known or suspected
to harbour transmissible microorganisms should be placed in a single room with
hand-washing and toilet facilities. A single room helps prevent director indirect
contact transmission or droplet transmission. The infected or colonised patient
can contaminate the environment or have difficulty in maintaining infection
control precautions to limit transmission of micro-organisms (a difficulty particularly
experienced by infants, children and patients with altered mental status). A
single room with appropriate air handling and ventilation is particularly important
for reducing the risk of airborne transmission of microorganisms from a source
patient to susceptible patients and other persons in hospitals.
Classification of isolation rooms
Class S—Standard Pressure Room
Standard pressure rooms are for patients who require contact or droplet isolation.
A standard room with normal air-conditioning is appropriate.
Recommended Elements
(a) A staff hand-wash basin within the room (b) An ensuite bathroom (c) A self-closing
door.
Optional Elements:
• A pan sanitiser near the room
• Label as a standard pressure isolation room.
Class N—Negative Pressure Room
Negative pressure rooms are for patients who require airborne droplet nuclei
isolation. The aim of placing persons in negative pressure rooms is to reduce
transmission of disease via the airborne route.
Recommended Elements
(a) Maintain a negative pressure gradient from the room to the airlock and the
ambient air. This is accomplished via a separate exhaust system dedicated to
each room, removing a quantity of air greater than that of the supply system.
Exhaust air ducts should be independent of the building’s common exhaust
air system to reduce the risk of contamination from back draught.
(b) Maintain an air change rate greater than or equal to 12 air changes per
hour, or 145 liters per second per patient (whichever results in the greatest
air quantity), when supply or exhaust air filters are at their maximum pressure
drop.
(c) Duct the exhaust directly to the outside to prevent exhaust air re-circulation.
(d) Draw exhaust air from low-level exhaust ducts approximately 150 millimeters
above the floor in the room.
(e) Locate the exhaust fan at a point in the duct system that will ensure the
duct is under negative pressure throughout its run within the building.
(f) Ensure supply air ducts are independent of the building’s common supply
air system.
(g) Design the supply air and exhaust systems to be of a constant volume system.
(h) Design the air supply to provide 100 per cent fresh air.
(j) Fit differential low-pressure instrumentation in a prominent location outside
the room.
(k) Fit a local audible alarm in case of fan failure.
(l) Ensure the room is as airtight as possible, with plasterboard ceilings,
well-sealed penetrations, tight-fitting doors and windows, and a door grille
designed for a controlled air path. Efficient sealing of the room will result
in better maintenance of pressure gradients with less load on the air-handling
plant.
(m) Install an ensuite bathroom.
(n) Fit a staff hand-wash basin within the room.
(0) Construct an airlock or anteroom for each room, with a pressure less than
the adjacent ambient pressure. The pressure differential between rooms should
be no less than 15 Pascal (Pa).
(p) Install a self-closing door, considering the direction of door swing in
relation to room pressure.
(q) Label the area as being a negative pressure isolation room.
(r) Fit the ducts with terminal high-efficiency particulate air (HEPA) filters
(or other failsafe back draught prevention system), when the sharing of exhaust
ducts with other isolation rooms is unavoidable. Install a high-efficiency bag
filter as a pre-filter to protect the HEPA filter.
(s) Fit the ducts with terminal HEPA filters (or other failsafe back draught
prevention system), when the sharing of supply ducts with other isolation rooms
is unavoidable. Install a high efficiency bag filter as a pre-filter to protect
the HEPA filter.
Class P—Positive Pressure Room
Some healthcare facilities use rooms with a positive pressure relative to the
ambient pressure to isolate profoundly immuno-compromised patients, such ascertain
transplant and oncology patients. The aim is to reduce the risk of airborne
transmission of infection to susceptible patients. Evidence for a protective
effect from positive pressure is largely limited to studies of patients at high
risk of nosocomial aspergillosis, where laminar airflow at ultra-high airflow
rates was used to create a positive pressure.
Evidence for the use of such rooms for other purposes is
lacking. Further, difficulties arise when the patient requiring protective isolation
is also infectious to others, particularly with airborne-spread infections (for
example, a renal transplant patient with varicella zoster).
Recommended Elements
(a) Maintain a positive pressure gradient from the room to ambient air via an
exhaust system that removes a quantity of air less than that of the supply system.
(b) Maintain an air change rate greater than or equal to 12 air changes per
hour, or 145 litres per second per patient (whichever results in the greatest
air quantity), when the supply airfilter is at the maximum pressure drop.
© Positive pressure rooms may share common supply air systems.
(d) Fit a terminal HEPA filter on the supply air inlet.
(e) Fit differential low-pressure instrumentation in a prominent location outside
the room.
(f) Fit a local audible alarm in case of fan failure.
(g) Ensure the room is as airtight as possible, with plasterboard ceilings,
well-sealed penetrations, tight-fitting doors and windows, and a door grille
designed for a controlled air path. Efficient sealing of the room will result
in better maintenance of pressure gradients with less load on the air handling
plant.
(h) Install an ensuite bathroom.
(j) Fit a staff hand-wash basin inside the room.
(k) Install a self-closing door, considering the direction of door swing in
relation to room pressure.
(l) Label as a positive pressure isolation room.
Optional Elements
Install an airlock or anteroom. To prevent the introduction of airborne contaminants
from the external environment, the air pressure within the airlock/anteroom
should be greater than the adjacent ambient pressure. Establish negative pressure
in the airlock relative to the ambient pressure so as to prevent the airborne
spread of infections (such as tuberculosis or chickenpox) from an infected immuno-compromised
patient. Alternatively, place the infectious patient in a ‘non-protective’
environment in a Class N room.
Number of isolation rooms required
General Principles
Healthcare facilities should use available data to help estimate the number
of isolation rooms required. Data should be collected prospectively from existing
facilities to assess the actual demand for, and use of, facilities to isolate
patients known or suspected to have an infection that requires a particular
form of isolation.
The assessment of such cases should include: The number
of patient admissions with infections known or suspected to require isolation.
The duration of isolation required.
Any clustering of cases which may be influenced by seasonal and other trends.
and the type of unit where patient isolation may be necessary. Data collected
over one year or longer provide more reliable estimates; these estimates help
determine peak needs for diseases with marked seasonal variation. Retrospective
data on cyclic epidemics of diseases may help determine ‘worst-case scenarios’,
although it may not be cost-effective for individual facilities to provide sufficient
isolation rooms for extreme circumstances.
Estimates of isolation room needs should also account
for
• Trends in disease in the general population and the particular population
served by the facility. • Demographic trends in the population served by
the facility.• Specialties of the health care facility, along with any
projected changes in the facility’s activities. The final assessment of
isolation room requirements should be made in consultation with involved clinical
specialists, engineers, architects and the infection control committee.
Class N Rooms
The isolation room requirements for persons known or suspected to have infections
requiring airborne precautions (such as chicken pox, measles and infectious
pulmonary and laryngeal tuberculosis) will determine the need for Class N rooms.
When calculating these requirements, it is important to consider suspected cases
of these infections: patients suspected of having tuberculosis, for example,
require such isolation until either the clinician excludes the diagnosis or
treatment renders the patient non-infectious. Larger health care facilities
achieve nursing care, economic and engineering benefits from co-locating class
N rooms. Special areas that require either one or more Class N rooms (or an
area with air handling to Class N standards) include: The emergency department,
Intensive care units (adult, paediatric, newborn) and procedure areas such as
bronchoscopy suites or sputum induction rooms.
Class P Rooms
Healthcare facilities should determine their need for such rooms using their
own data on local threats from pathogens such as Aspergillus, as well as evidence
(from both within and beyond the facility) on the role of particular environments
in protecting vulnerable patients.
Environmental control
The aim of environmental control in an isolation facility is to control the
airflow so as to reduce the number of airborne infectious particles such that
they are unlikely to infect another person within the environment of the healthcare
facility. This is achieved by controlling the quality and quantity of intake
and exhaust air, diluting infectious particles in large volumes of air, maintaining
differential air pressures between adjacent areas, and designing patterns of
airflow for particular clinical purposes.
Pressure Gradients
• The minimum differential pressure between the isolation room and adjacent
ambient pressure areas should be 30 Pa if the room has an airlock and 15 Pa
if the room does not have an airlock. • The gradient between successive
pressure areas should not be less than 15 Pa. • Air Filter Efficiencies.
• Air filtration should comply with the following requirements
Class N
• Minimum filter efficiency of 25 per cent • Use of a terminal HEPA
filter on exhaust to prevent back draught (optional). • Use of high-efficiency
pre-filters before HEPA filters.
Class P
• Use of a terminal HEPA filter on supply air. Use of a terminal HEPA filter
on exhaust to prevent back draught (optional). Use of high-efficiency pre-filters
before HEPA filters.
Supply Air and Exhaust Duct Design
The ductwork of a negative pressure isolation room must not communicate with
the ductwork of the rest of the hospital. Ductwork should be designed to reduce
the possibility of cross contamination in the event of fan failure. This can
be accomplished by ducting each negative pressure isolation room separately
from the air-handling unit. Separate long duct work runs from the air handling
unit increase static pressure and reduce the contaminated airflow in the event
of a failure. Back draught dampers may provide similar protection, but designers
must consider the problems of damper failure.
Supply and exhaust systems should be designed as failsafe (for example, using
duplex fans) to prevent contamination of any area within the facility in the
event of fan failure. The exhaust fan should be located at a point in the duct
system that will ensure that the entire duct is under negative pressure within
the building.
Air distribution
Air distribution systems should be designed to provide a
high effective ventilation rate. It may be difficult to achieve consistent mixing
throughout the room. Placement of multiple, uniformly distributed supply air
diffusers in the ceiling, with several low-level exhausts, will create an effective
displacement pattern. True displacement ventilation will be difficult to achieve,
but the effective ventilation rate will be high. Diffusers should be designed
or selected to entrain large amounts of air with the aim of achieving perfect
mixing.
The design and balance of the ventilation system should ensure that air flows
from less contaminated to more contaminated areas. Air in an open Class N room,
for example, should flow from corridors into the isolation room to prevent the
spread of airborne contaminants from the isolation room to other areas. Within
the room, the air should follow similar principles: in a Class N room, the air
should pass over first the staff then the patient, and in a Class P room, the
air should pass over first the patient then the staff. Air distribution should
reduce the staff’s exposure to potential airborne droplet nuclei from infectious
patients, accounting for the positions of the staff and the patient, and the
procedures undertaken in the isolation room.
Air Change Rates
For rooms in Classes N and P, air change rates greater than
or equal to 12 air changes per hour or 145 litres per second per patient, whichever
results in the greater air quantity, should be achievable when the filters have
reached their maximum pressure drop. The selection of 12 air changes per hour
is largely a matter of convention. An air change rate of 12 may cause stratification,
whereas higher air change rates (say, 20) may cause turbulence. An air change
rate of 15 may be a desirable compromise, accounting for both dilution of airborne
agents and air distribution.
Exhaust Discharge Location
Position the exhaust discharge duct to prevent the contamination of intake air.
In some situations the discharge plume may need to be modelled to prevent entrainment.
Monitoring of
Room Pressure
Monitor pressure by using an analogue gauge (such as a differential low-pressure
gauge) or reliable stand-alone digital instrumentation. Locate gauges in a prominent
location outside the room. Select an instrument with an appropriate scale—that
is, with the maximum pressure being approximately 80 percent of full-scale deflection.
Monitor the actual airflow with a flow switch, and fit a local audible alarm
in case of fan failure.
Minimum Fresh Air Requirements
In Class N rooms, 100 per cent fresh air (no recirculating air) will achieve
the most effective dilution of airborne micro-organisms. If any degree of air
re-circulation is contemplated, consider whether the controls will adequately
deal with droplet nuclei, dust and odor.
Minimising of Room Air Leaks
Inspect rooms for air leakage points during and after construction. Pressures
within the room will be easier to maintain, with less load on the air handling
plant, if the rooms have plaster ceilings, tight-fitting doors and windows,
and sealed service penetrations.
Routine Performance Monitoring and Maintenance
Establish performance protocols before bringing rooms into service. Define persons
responsible for the operation, monitoring and maintenance of rooms. Provide
regular in-service training for staff who use the facility to ensure that they
understand the functions of the room and how to read and interpret the monitoring
instrumentation. The nursing care plan of the isolated patient must include
daily monitoring and documentation of room and airlock pressures. Engineering
staff should undertake system performance monitoring via a planned maintenance
system. Maintenance staff should check items such as:
• The air change rate • Supply air and exhaust quantities • The
terminal HEPA filters • Exhaust registers
• Room pressure gauges • Any damage to the room interior • Supply
and exhaust fans • Room seals and the door closer • The hand wash-basin
and ensuite plumbing, and
• Room signage.
Plant Back-up Systems
A back-up emergency power supply should be available to ensure fans, alarms
and monitoring systems do not fail if the main power supply is disrupted.
Isolation Room Interiors
The design, materials and construction of the interior surfaces of an isolation
room are critical to the room’s performance in containing infections.
Aim to: • Facilitate cleaning • Minimise dust-collecting areas •
Minimise areas that may remain contaminated between patients • Facilitate
patient care and comfort.
Preferred features include: • Continuous impervious surfaces such as welded
vinyl, epoxy coatings or similar durable surfaces. • Welded vinyl floors
cover up the walls, and wall finishes that are durable and easy to clean (for
Example welded vinyl). The use of carpet is discouraged because it is difficult
to clean. • Guard rails to protect the walls from damage by beds and mobile
equipment.
• Epoxy-coated or stainless steel joinery, which is
easier to clean than uncoated timber. • Windows designed to avoid pelmets
and dust collection areas. • Washable curtains. • A wall-hung toilet
pan and basin with non hand-operated taps.
The writer is officer in charge hospital projects at army
hospital, New Delhi
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