Ultra clean ventilation for operating theatres

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Hospital Ventilation

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Operating Room Ventilation
The supply of air to an operating room has four main functions:
• To dilute airborne contamination.
• To control air movement within the suite such that the
transfer of airborne contaminants from less clean to cleaner
areas is minimised.
• To control the temperature and, if necessary, the humidity of
the space.
• To assist the removal of, and dilute, waste anaesthetic gases.

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Typical Operating Room Ventilation System
Air Handling Unit (AHU)

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ULTRA-CLEAN OPERATING ROOM

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Inventors of Ultra Clean Ventilation
• In the early 1960s
Howorth Air
Technology Ltd,
working closely with
Sir John Charnley,
developed the world’s
first UCV

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Ultra Clean Ventilation
• UCV – Ultra Clean Ventilation
• Laminar (Unidirectional) Air Systems
• Ultra Clean Operating Room
• Ultraclean Air Systems
• Clean Air Canopy
• Ultra Clean Canopy
• Cleanroom
• Charnley-Howorth System
Common Names

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Ultra Clean Air - Definition
“Ultra-clean air is defined
as that containing not more
than 10 CFU/m3 ”
Generally Accepted Definition
Colony-forming unit (CFU) is a measure of viable
bacterial or fungal numbers, CFU measures only
viable (live) cells
(0.3 CFU/ft3)

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Where are UCVs Used?
• Orthopaedics
• Ophthalmology
• Cardiothoracic Surgery
• Neurosurgery
• Transplant Surgery
• Endoscopy
• Plastic Surgery
• Various Day Surgeries
• Any invasive “Clean” Surgery
What types of surgery are performed
under Ultra Clean Ventilation Systems?

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UCV use in Orthopaedic Surgery
• UCV systems are used extensively in orthopaedic operating
rooms
• Although Arthroplastic procedures are where UCVs are most
frequently employed. Other types of orthopaedic surgery,
including, spinal surgery and the repair of major fractures
also utilise ultra clean air systems

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The World’s 1st UCV System
• Charnley’s solution was the
Ultra Clean Ventilation (UCV)
system
• Known affectionately as the
“greenhouse”, the system
enclosed both the patient and
the surgical team
• Where they were bathed in a
constant supply of filtered
clean air

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Ultra Clean Ventilation Systems

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Types of UCV System in Common Use
• Horizontal Systems have been largely discredited and are
only very occasionally used
• Vertical systems fall into two main classes…
• Utilise main ventilation air with no
additional fans
• Low number of air changes per hour,
typically 15 – 30 ACH
• Downflow velocity typically low, i.e.
less than 0.2 m/s (40 fpm)
Low Flow Systems
• Supplement the main ventilation air
supply with auxiliary fans
• High number of air changes per
hour, typically >100 ACH
• Downflow velocity medium to high,
i.e. 0.2 – 0.5 m/s (40 - 100 fpm)
High Flow Systems

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Air Curtain UCV
• The best systems utilise a central laminar air diffuser surrounded on all
four sides by an air curtain diffuser
• Many systems are low flow and therefore suffer from not being able to
provide adequate dilution

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Air Curtain UCV

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Comments
• Developed from a cleanroom system
• Canadian design to Canadian & US Standards
• Relatively Low Velocity in centre, below HTM-03-01
requirements
• High velocity of air curtain air causes entrainment. (See
smoke pattern below)
• No examples in UK although being considered for project in
Ireland

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Partial Wall UCV with Low Level Returns
• Can provide good performance, providing they have a sufficiently large
area and adequate levels of flow are employed
• Low flow systems and undersized systems can suffer from entrainment
and poor levels of dilution

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Partial Wall UCV - Low Level Returns

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Partial Wall UCV - Low Level Returns

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Comments - Partial Wall UCV with Low Level Returns
• Principally European design
• Low velocity systems that need upgrading to match HTM requirements
• Low level recirculation ducts around theatre cause obstruction, infection
control issues, and can themselves be obstructed by theatre equipment
• Usually square, but can be made to different configurations
• Tend to utilise nylon CG screens as diffuser which are difficult to clean
and therefore present another potential infection control issue
• Usually a 50% recirculation of supply air means higher running costs
• Several units have integral cooling coils to combat air buoyancy to
achieve HTM compliance
• Can be costly to install due to increased infrastructure & service
requirements i.e. additional recirculation ductwork, cooling coils, chilled
water pipework etc.

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Fully Enclosed UCV
• Provides very good protection providing suitable flow rates are utilised
• Obvious disadvantage is the restricted work area for the surgical team
• Rarely seen in modern operating rooms

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Closed UCV

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Comments
• Excellent downflow & non-entrainment characteristics.
• Lower CFU count at wound site than standard UCVs
• Extremely constricting for the theatre staff and for
equipment usage.

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Partial Wall Style of UCV
• This type of system is used extensively in the UK and many parts of
Europe
• This system utilises a partial wall and ceiling mounted returns to develop
the air flow pattern

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Partial Wall UCVs

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Partial Wall UCVs

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Comments
• Fully compliant with HTM 03-01
• Recognised standard in all orthopaedic ORs in UK
• Usually available in 3.5 x 3.5 m, 3.2 x 3.2m, 2.8 x 2.8m clean
zones. Although other sizes can be made to order.
• Side screens prevent entrainment although can be restrictive
to OR equipment choice. Sliding screen options are available
to combat this problem.
• Usually steel perforated diffusers which are easily cleaned
• No requirement for low level recirculation
• Modular construction of UCV allows speedy installation
• Performance well understood by validation engineers

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Screenless Canopy – Low Level Recirculation
• This type of system is used extensively in Europe, but as yet is largely
unproven in the UK
• This system utilises low level recirculation to develop the air flow pattern

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Screenless Canopy – Low Level Recirculation

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Low Level - Return Air Ducts
Return Duct
Inlets
Fan Housing

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Comments
• Principally European design
• Low velocity systems that need upgrading to match HTM requirements
• Low level recirculation ducts around theatre cause obstruction, infection
control issues, and can themselves be obstructed by theatre equipment.
• Usually square, but can be made to different configurations. See image
• Tend to utilise nylon CG screens as diffuser which are difficult to clean
and therefore present another potential infection control issue
• Usually a 50% recirculation of supply air means higher running costs.
• Several units have integral cooling coils to combat air buoyancy to
achieve HTM compliance.
• Can be costly to install & maintain due to increased infrastructure &
service requirements i.e. additional recirculation ductwork, cooling coils,
chilled water pipework etc.
• Lack of side screens improves equipment selection.

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Screenless Canopy – Integrated Recirculation
• The partial wall(screened) version of this system used throughout the UK
• This improved screenless system requires no partial wall or low level
recirculation ducts. It utilises ceiling mounted returns & patented coanda
technology to develop the air flow pattern

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Screenless Canopy – Integrated Recirculation

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Comments
• Fully compliant with HTM 03-01
• Developed & improved from standard UCV technology
therefore maintenance, running costs are low and reliability
is proven
• Fully integrated system i.e. no need for low level
recirculation ducts, additional fans or cooling coils.
• Independently validated
• Patented coanda technology ensures no entrainment
• Lack of side screens improves equipment selections
• Unique system to market, designed & manufactured in the
UK.

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Modular or Integrated UCV System
Operating Room

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Remote UCV System
Operating Room

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Exflow – Exclusive Benefits
• Unique Exponential airflow
pattern
• No entrainment, even
without full side walls
• Up to 500 air changes an
hour
• Larger clean zone protects
instruments
• Graded air flow, higher
central velocity overcomes
thermal plumes

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Exflow – Further Benefits
• Greater patient protection
• Improved OR staff comfort
• Reductions in post-operative
infection
• Less revision surgery
• Improved OR utilisation
• Reduced litigation risk

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Performance Validation
• Air velocity measurements
• Air flow balancing
• Flow Visualisation
• Entrainment testing
• Acoustic testing
• Temperature & humidity
• Particulate Monitoring (viable
& non-viable)
• Microbiological testing (settle
plates, swab testing, etc)
Common UCV Performance Testing

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Body Exhaust Systems & Surgical Helmets

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Body Exhaust Systems
• Originally invented by Sir John Charnley & Hugh Howorth at
the same time as the first UCV
• Designed to remove contaminants from the
immediate vicinity of the surgeon before
they become airborne
• Works by generating a local vacuum, pulling
in shedded skin cells through a distribution
pipe worn on the body
• The pipe is connected back to the UCV

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Body Exhaust Systems
• A more advanced version
incorporates a mask &
helmet
• This improves patient
protection & adds a comms
system
• It also affords the surgeon a
level of protection from
blood splatter & flying bone
debris

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Body Exhaust Systems
• Numerous trials have indicated that the body exhaust
system can provide an enhanced level of operating room air
cleanliness
• In use with Howorth’s Exflow system, level of less than 1
CFU/m3 have been measured

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Microbiological Air Sampling – Typical Results
1
10
100
CFU/Cubicmeter
Normal OR Exflow Exflow + OC Exflow + BEX
OR - Operating Room BEX – Body Exhaust
OC – Occlusive Clothing CFU – Colony Forming Unit
Key
50 - 250
5 - 10
< 5
1

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Relevant Guidelines, Legislation
& Standards

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Relevant European Guidelines
• HTM 03-01, Specialised ventilation for healthcare premises
− A UK Guideline that is extensively followed, Revised in 2007
• VDI 2167, Building services in hospitals, HVAC Code of
Practice
− A German standard also adopted in some other European Countries
• DIN 1946 T4
− A German standard also adopted in some other
European Countries, has just had a major rewrite
and has adopted many aspects of HTM-030-01

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RELEVANT REGULATIONS / GUIDELINES
• HTM 03-01 (ventilation)
• HTM 02-01 (Medical gases)
• HTM 06-01 (Electrical Installation)
• HTM 08-01 (Acoustics)
• HTM 64 (Sanitary Ware)
• HTM 63 & HTM 70 (Fitted Storage
Furniture)
• HTM 58 (Internal Door Sets)
• HBN 26 (Facilities for Surgical
Procedures)
• HTM 2027 (Domestic Water Supplies)
• MODEL ENGINEERING SPECIFICATION
CO4
• MODEL ENGINEERING SPECIFICATION
CO2
• BRITISH STANDARDS
• BUILDING REGULATIONS (Particularly L2)
• 17TH EDITION ELECTRICAL REGULATIONS
• CIBSE GUIDELINES