ASHRAE RESEARCH PROPOSAL
02/16/16
MILTON GOLDMAN
ISSUES CONCERNING OPERATING ROOM MECHANICAL SYSTEMS
Proper operating room airflow parameters are not clearly defined.1 Solutions to the
questions of OR airflow are critical because they are part of the larger questions of how
to prevent surgical site infections and how to prevent the spread of infectious disease into
and out of the operating room.2 Occurrence and spread of infections are influenced by
many factors other than HVAC systems. Some of these factors are patients’ nutrition
and resistance to infection, the type of surgery being performed3, surgical technique4,
health of operating room personnel, operating room traffic5, proximity of the OR to other
hospital areas, OR cleaning procedures, OR clothing6, adherence to sterile technique and
others. 7 ASHRAE can suggest standards only in the area of mechanical systems. Before
coming to conclusions of optimal mechanical standards, it is imperative that ASHRAE’s
research be in consultation with and in coordination with the efforts of other disciplines
concerned with the overall problem of operating room infections.
1) CFM vs. ACH
Smaller OR’s sized on the basis of ACH may receive less optimal airflow as more people
are added to the room.8 On the other hand, as more people and more equipment are
added the small OR, a significant volume of the OR is taken up by space occupying
matter and, the de facto air change rate increases, a compensatory phenomenon. For
instance, a draped patient and operating table occupy 36 to 40 cubic feet and people each
occupy 3 to 4 cf, thereby reducing the volume of air to be changed. Whether delivered
on the basis of CFM or on the basis of ACH, our sizing criteria should take into
consideration the size of the room, the type of surgery being performed, the amount of
equipment in the room, the number of people allowed into the room, the experience of
“Ventilation and Exhaust Air Requirements for Hospitals – Part I: Standards”, Chaddock, J.B., ASHRAE
Tranactions 3000 (RP-312) 350-371.
1
“Importance of Air Quality and Related Factors in the Prevention of Infection in Orthopedic Implant
Surgery”, Gosden, P.E., MacGowan, A.P., et al; Journal of Hospital Infection (1998) 39, 173-180
2
“The Relationship of Genitourinary Tract Procedures and Deep Sepsis After Total Hip Replacements”,
Irvine, Robert; Surgery, Gynecology & Obstetrics ; 139:701, November, 1974.
3
4
“The Surgical Isolation Bubble System”, Scott, F. Brantley; Lecture (1984) & personal communication.
“Guideline for Prevention of Surgical Site Infection, 1999”, April, 1999; Infection Control and Hospital
Epidemiology; 20:4 p. 247-278
5
“Reducing Wound Infections: Improved Gown and Drape Barrier Performance”, Moylan, J.A., et al;
Archives of Surgery (1987) 122, 152-157.
6
7
Hospital Infections, Third Edition, Bennett, J.V. Ed; Little, Brown and Company (1992)
“Health Care Ventilation Standard: Air Changes Per Hour or CFM/Patient?” Marshall, J.E; ASHRAE
Journal (Sept 1996) 27-29
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people in the room [inexperienced and untrained people who may be less familiar with
sterile technique are more apt to contaminate in a confined space], and whether the room
is used for teaching and/or for innovative procedures. It is therefore necessary to classify
OR’s more closely to the above concerns so that we may better determine the amount and
the quality of air optimal for each classification.
2) OR CLASSIFICATION
The present method of classifying operating rooms (colony forming units per cubic
meter) does not take into consideration many of the issues that should influence air
quality and amount.9 The likelihood of cfu “impaction” is a more accurate prognosticator
of infection than cfu’s per cubic meter. Better definitions and better measuring
techniques are necessary to settle this question.10 Consultation and coordination with the
medical community are the necessary first steps. The American College of Surgeons
classification system is as follows: Class 1- Max 1 bacterial particle per cf; Class 5- Max
5 bacterial particles per cf; & Class 20- Max 20 bacterial per cf. This does not indicate to
us (ASHRAE), to surgeons, to hospital administrations nor to architects the ventilation
methods needed for various types of operating rooms. Classification is the most critical
operating room ventilation topic and begs for definition. Liaison should be established
with The American College of Surgeons as soon as practicable.
3) SURGICAL SITE INFECTION
An important step in determining the efficacies of various airflows as they pertain to
surgical site infection is to determine if a problem actually exists.11 The CDC does not
have data on surgical site infections other than that already reported in the literature.12
Statistics regarding surgical site infections are difficult to obtain. Many institutions
consider their infection rates to be proprietary information and will not divulge their data.
Prosthetic infections are generally prevented by antibiotic irrigation during surgery and
by antibacterial impregnated implants, techniques not mentioned in the classic “air flow
vs. infection” literature. This question can be approached on several fronts:
A) A national hospital survey can be performed.
“Importance of Air Quality and Related Factors in the Prevention of Infection in Orthopedic Implant
Surgery”, Gosden, P.E., MacGowan, A.P., et al; Journal of Hospital Infection (1998) 39, 173-180
9
“Ventilation and Exhaust Air Requirements for Hospitals – Part I: Standards”, Chaddock, J.B.,
ASHRAE Tranactions 3000 (RP-312) 350-371.
10
11
“Laminar Airflow and Surgical Wound Infections”, Belkin, N.; AORN Journal (1998) 68:2 273-275.
“Guideline for Prevention of Surgical Site Infection, 1999”, April, 1999; Infection Control and Hospital
Epidemiology; 20:4 p. 247-278.
12
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This would be quite tricky. The survey would have to be short in order to be
answered. The data would have to be statistically valid. A professional polling
firm should set up the survey and professional statisticians should analyze the
data.
B) Contact should be made with the major hospitals and academic institutions that
SP-91 members have special relationships with such as Duke and Massachusetts
General. These institutions are at the apex of medical care in this country and are
forthright with nothing to hide.
C) Thorough search of the medical literature, specifically the orthopedic
literature regarding control of surgical infections is needed. Much of the data we
are using is from the same institutions, some of which seem to be “selling” their
techniques.13
D) Contact and coordination with the American College of Surgeons and with
major orthopedic societies is necessary to determine the extent of the airflow
problem and if environmental measures have a further contribution to make
toward the control of surgical site infections.
E) ASHRAE could sponsor an interdisciplinary conference on surgical site
infection.
4) SQUAMES
Many questions arise concerning surgical site infections. Infections are caused by
bacteria that get into the wound/surgical site. The bacteria are carried through the air on
“squames”. Squames are small groups of dead skin cells shed by the thousands by people
all the time, including operating room personnel.
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How large are squames?14 [Important filtration information]
How dense are squames? [Floatation]
Are pathological bacteria spread independently of squames?
Do different people shed squames at different rates?
Do people with dry skin shed squames more readily than do people with oily skin?
Do people shed more squames in dry climates vs. humid climates, in cold climates vs.
hot climates?
 Do people shed squames immediately after a shower at the same rate that they shed
them four hours later?
“Prevention of Airborne Infection During Surgery”, Howorth, F.H.; ASHRAE Transactions
CH-85-06 No. 2.
13
“Airborne Particulates in the OR Environment”, Edmiston,C., Sinski, S., et al; AORN Journal (June
1999) 69:(6) 1169-1183.
14
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 Could squame shedding be significantly reduced by having the operating room
personnel shower immediately prior to a sensitive case?
 Would bath oil after the showers reduce squame shedding?
 Are bacteria introduced into the OR with equipment being brought into the room
during surgery? If so, could the equipment be effectively sterilized by passage
through an ultra violet light chamber?15 For how long? An ozone chamber?
 Particles remain in the room after cleaning. Would “streamlining” equipment,
removing sharp edges, cavities and crevices, affect easier and therefore more
thorough cleaning of surfaces? Would rounding or coving all corners of the room
affect better cleaning?16
Perhaps the answers to these questions are already answered in the dermatology and/or
nursing literature, and, perhaps not. A finding of decreased desquamation by OR
personnel after showering might influence the architecture of surgical suites. The point is
that surgical site infections are a multi-faceted problem and should be approached in
coordination with several disciplines and institutions. These institutions and disciplines
should include The American College of Surgeons, the CDC, NIH, AORN, AHA,
infectious disease specialists, orthopedists, microbiologists, dermatologists, the AIA and
ASHRAE.
5) OR AIRFLOW RESEARCH
Questions regarding operating room airflow are as follows:
 What is the optimal velocity of turbulent air flowing over the operative site to prevent
impaction of squames and bacteria?17 Is there a critical degree of turbulence?18 Can
a formula or a dimensionless fraction be developed to define an acceptable degree of
turbulence?19
 Can laminar airflow reach the surgical site?20 Is laminar flow preferable?21
15
“Highlights of CDC’s Guidelines on Surgical Infection”, OR Manager (July 1999) 15:7 9-15.
16
Guidelines for Construction and Equipment of Hospitals and Medical Facilities; (1992-93) The
American Institutes of Architects Press.
“Importance of Air Quality and Related Factors in the Prevention of Infection in Orthopedic Implant
Surgery”, Gosden, P.E., MacGowan, A.P., et al; Journal of Hospital Infection (1998) 39, 173-180.
17
“Assessment of Airborne Bacterial Contamination of Clean Wounds: Results in a Tissue Model”,
Taylor,G.J.S.; Leeming, J.P., et al; Journal of Hospital Infection (1992) 22, 241-249.
18
“Operating Room With Turbulent Airflow”, Zamuner, N.; ASHRAE Tranactions (1986) 92-2A, 343349.
19
20
“Ultraclean Laminar Airflows”, Friberg, B.; AORN Journal 67:4 841-851.
“Ultraclean Air and Antibiotics for Prevention of Postoperative Infection”, Lidwell, O.M., et al; Acta
Orthopaedica Scandinavica (1987) vol. 58, p. 4-13.
21
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 Does laminar flow increase impaction22 and resulting infection?23
 Do the possible benefits of laminar flow warrant its higher first cost and its increased
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energy consumption?24
What is the optimal direction or directions of airflow to prevent impaction or settling
of squames and bacteria?25
What is the optimal arrangement of supply and return to prevent impaction and
settling?26
Can OR airflow be stratified to prevent particles27 below table level from migrating
or from being blown upward?28
Can the plume described by Dr. John Woods be utilized for particle removal?29 Can
laser and electrocautery plumes be removed with such a system?30
Can the anesthesia screen or a specially shaped anesthesia screen be used as an airfoil
to direct airflow upward and away from the field into a strategically placed return?31
Can a nozzle be used to direct air in an optimal direction over the field?32 ,33
“Infection Rates After 3175 Total Hip and Knee Replacements Performed With and Without a
Horizontal Unidirectional Filtered Air-Flow System”, Salvati,E.A, Robinson,R.P., et al; Journal of Bone
and Joint Surgery (1982) 64-A:(4) 525-535.
22
“Infection and Interposition Between Ultraclean Air Source and Wound”, Taylor, G.J.S., Bannister,
G.C.;Journal of Bone and Joint Surgery (1993) 75-B, 503-4.
23
“Ventilation Requirements in Hospital Operating Rooms – Part II: Energy and Economic Implications”,
Woods, J.E., et al; ASHRAE Transactions 3002 (RP-202) 427-449.
24
“Zoned Exponential, Vertical and Horizontal Ultra-clean Laminar Airflows”, Friberg, B., Acta
Orthopaedica Scandinavica (1998) 69 (2) 169-172.
25
26
“Operating Room Air Distribution Effectiveness”, Lewis, J.R.; ASHRAE Transactions DE-93_22-2.
“Airborne Particulates in the OR Environment”, Edmiston,C., Sinski, S., et al; AORN Journal (June
1999) 69:(6) 1169-1183.
27
“Zoned Exponential, Vertical and Horizontal Ultra-clean Laminar Airflows”, Friberg, B., Acta
Orthopaedica Scandinavica (1998) 69 (2) 169-172.
28
“Ventilation Requirements in Hospital Operating Rooms – Part I: Control of Airborne Particles”,
Woods, J.E., et al; ASHRAE Transactions 3001 (RP-202) 396-426.
29
“Bacteriophage -174 as an Aerobiological Marker for Surgical Plume Generated by the
Electromagnetic Field Focusing System”, Price, J.A., et al; Journal of Hospital Infection (1992) 21, 39-50.
30
“Inefficiency of Upward Displacement Operating Theatre Ventilation”, Friberg, B., et al; Journal of
Hospital Infection (1996) 33, 2163-272.
31
“Air Control in Operating Theatres- Comparison and Evaluation of Attainable Germ Counts in the Air”;
Schmidt, Dr.-Ing Peter; HKH vol. 38:3, p. 145-153.
32
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 Can such a nozzle be suspended from the ceiling and be moved to optimal positions
in the same manner that the operating lights are moved?34
 Does positive pressure in the OR potentially push dangerous organisms into the
hospital environment?35 Should clean cases be done in positive pressure rooms and
dirty cases in negative pressure rooms? Or, should all operating rooms have
anterooms negative to both the OR and to the hallway?
 Is there an unobtrusive and relatively inexpensive way of measuring particle settling
and movement during actual surgery?36 Could such a method be used universally for
quality control?37,38
These questions and many others can be answered and valid standards established with well
controlled [medical/statistical sense of “control”], integrated, multi-parameter and reproducible
research.
The following is a recommendation for a facility that could answer many of the above questions.
A chamber simulating an operating room should be built in a laboratory and
retained after the research is concluded so that future ideas can be tested
in the same environment. The chamber should be able to contain moving models
of people and equipment so that the interior environment most simulates that of
an actual operating room.
The chamber should have visual capability of observing and recording airflow;
particle generators, various methods of counting particles such as electronic and
radio isotope means as well as the classic culture techniques; humidity control;
temperature control; velocity measurement and control; and, pressure
measurement and control. Capability of simultaneously measuring various
parameters, and, simultaneously measuring them in multiple locations are
“Measurement of Germ Counts and Spread of Air Bourne Bacteria in Operating Theatres Equipped with
the Air Control System ‘Air Supply Ceiling with Supporting Flow’”, Renger, P.; Weiss Technik GMBH,
D-6301 Reiskirchen.
33
“The Effect of a Portable HEPA-Filtered Body Exhaust System on Airborne Microbial Contamination in
a Conventional Operating Room”, Infection Control and Hospital Epidemiology (July 1996) 17:7 419-422.
34
“Transport of Surgically Produced Aerosols in the Operating Room”, Buchanan, C.R., Dunn-Rankun,
D.; American Industrial Hygiene Association Journal (1998) 59, 393-402.
35
“Aerobiology in the Operating Room – A Review”, Hambraeus, A.; Journal of Hospital Infection (1988)
11 (Supplement A), 68-76.
36
“Correlation Between Surface and Air Counts of Particles Carrying Aerobic Bacteria in Operating
Rooms with Turbulent Ventilation”, Friberg, B.; Journal of Hospital Infection (1999) 42: 61-68.
37
“Inconsistent Correlation Between Aerobic Bacterial Surface and Air Counts in Operating Rooms with
Ultra-clean Laminar Airflows: Proposal of a New Bacteriological Standard for Surface Contamination”,
Friberg, B., Journal of Hospital Infection (1999) 42: 287-293.
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necessary. Electronic data storage and access is also necessary.
Any and all airflow configurations could be tested in such a chamber.
The chamber should be to the ASHRAE committee on hospitals what
wind tunnels are to the aerospace industry.
Correlation should be made with the various methods of measurement
so that the most accurate and economical method that would be least intrusive to
actual surgery can be determined.
A smaller microbiological chamber could be constructed (or a microbiological
hood adapted) to measure float vs. settling parameters of various bacteria,
particles and squames during various velocity and turbulence conditions.
If findings from the above facilities yield fruitful information and this information
is to be utilized for determining standards, a second facility with independent
investigators should be commissioned to confirm the findings of the first
facility.[Koch’s postulates]
The two facilities should be at different altitudes in case air density influences the
float vs. settle characteristics of various particles. A correction factor could
possibly be developed.
6) COMPUTER ANANLSIS
A computer model of an operating room incorporating all of the above
characteristics and correlated with the above findings should be developed with
the intent of eventually reducing the need for physical research.
7) COORDINATION
The above studies should be coordinated and conducted simultaneously so that
the findings in one arena can influence the direction of research in the other
arenas. This would produce unified research, would produce timely data and
would reduce unnecessary research thereby reducing costs.
Coordination with other ASHRAE technical committees is advisable to answer
whether 100% outside air with heat exchange capability is preferable for
operating rooms. Can ultraviolet radiation and/or ozone generation be used to
reduce the need for HEPA filtration?
Industry should be allowed to participate in this program in a manner designed by
ASHRAE. Special and/or new equipment may be required for testing. New
products may result from these studies. Industry may be willing to invest in the
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program if allowed to benefit from the results. The American College of
Surgeons, The Association of Operating Room Nurses, The American Hospital
Association, the NIH and similar international organizations may be interested,
indeed anxious, to participate in such overall and conclusive research.
NOTE:
The references cited herein are often presented as suggested reading on a topic or as the
stimulus for a question rather than as direct authentication of a statement. Below is a
condensed list of suggested references:
Guidelines for Construction and Equipment of Hospitals and Medical Facilities; (1992-93) The
American Institutes of Architects Press.
“Guideline for Prevention of Surgical Site Infection, 1999”, April, 1999; Infection Control and
Hospital Epidemiology; 20:4 p. 247-278.
Hospital Infections, Third Edition, Bennett, J.V. ed; Little, Brown and Company (1992).
“Operating Room Air Distribution Effectiveness”, Lewis, J.R.; ASHRAE Transactions DE-93_222.
“Ventilation and Exhaust Air Requirements for Hospitals – Part I: Standards”, Chaddock J.B.,
ASHRAE Tranactions 3000 (RP-312) 350-371.
“Ventilation and Exhaust Air Requirements for Hospitals – Part II: Odors”, Chaddock J.B.,
ASHRAE Tranactions 3000 (RP-312) 372-395.
“Ventilation Requirements in Hospital Operating Rooms – Part I: Control of Airborne Particles”,
Woods, J.E., et al; ASHRAE Transactions 3001 (RP-202) 396-426.
“Ventilation Requirements in Hospital Operating Rooms – Part II: Energy and Economic
Implications”, Woods, J.E., et al; ASHRAE Transactions 3002 (RP-202) 427-449.
ASHRAE Standard 62-1989.
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