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Design of Hospital Operating Room Ventilation using Computational Fluid Dynamics
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.ORCID iD: 0000-0002-9361-1796
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Utforma operationssalars ventilationssystem med hjälp av beräkningsströmningsmekanik (Swedish)
Abstract [en]

The history of surgery is nearly as old as the human race. Control of wound infection has always been an essential part of any surgical procedure, and is still an important challenge in hospital operating rooms today. For patients undergoing surgery there is always a risk that they will develop some kind of postoperative complication.

It is widely accepted that airborne bacteria reaching a surgical site are mainly staphylococci released from the skin flora of the surgical staff in the operating room and that even a small fraction of those particles can initiate a severe infection at the surgical site.  Wound infections not only impose a tremendous burden on healthcare resources but also pose a major threat to the patient. Hospital-acquired infection ranks amongst the leading causes of death within the surgical patient population. A broad knowledge and understanding of sources and transport mechanisms of infectious particles may provide valuable possibilities to control and minimize postoperative infections.

This thesis contributes to finding solutions, through analysis of such mechanisms for a range of ventilation designs together with investigation of other factors that can influence spread of infection in hospitals, particularly in operating rooms.

The aim of this work is to apply the techniques of computational fluid dynamics in order to provide better understanding of air distribution strategies that may contribute to infection control in operating room and ward environments of hospitals, so that levels of bacteria-carrying particles in the air can be reduced while thermal comfort and air quality are improved.

 A range of airflow ventilation principles including fully mixed, laminar and hybrid strategies were studied. Airflow, particle and tracer gas simulations were performed to examine contaminant removal and air change effectiveness. A number of further influential parameters on the performance of airflow ventilation systems in operating rooms were examined and relevant measures for improvement were identified.

It was found that airflow patterns within operating room environments ranged from laminar to transitional to turbulent flows. Regardless of ventilation system used, a combination of all airflow regimes under transient conditions could exist within the operating room area. This showed that applying a general model to map airflow field and contaminant distribution may result in substantial error and should be avoided.

It was also shown that the amount of bacteria generated in an operating room could be minimized by reducing the number of personnel present. Infection-prone surgeries should be performed with as few personnel as possible. The initial source strength (amount of colony forming units that a person emits per unit time) of staff members can also be substantially reduced, by using clothing systems with high protective capacity.

Results indicated that horizontal laminar airflow could be a good alternative to the frequently used vertical system. The horizontal airflow system is less sensitive to thermal plumes, easy to install and maintain, relatively cost-efficient and does not require modification of existing lighting systems. Above all, horizontal laminar airflow ventilation does not hinder surgeons who need to bend over the surgical site to get a good view of the operative field.

The addition of a mobile ultra-clean exponential laminar airflow screen was also investigated as a complement to the main ventilation system in the operating room. It was concluded that this system could reduce the count of airborne particles carrying microorganisms if proper work practices were maintained by the surgical staff.

A close collaboration and mutual understanding between ventilation experts and surgical staff would be a key factor in reducing infection rates. In addition, effective and frequent evaluation of bacteria levels for both new and existing ventilation systems would also be important.

Abstract [sv]

Tidigt i mänsklighetens utveckling har kirurgin funnits med i bilden. Hantering av infektioner har genom tiderna varit en oundviklig del av alla kirurgiska ingrepp, och finns kvar ännu idag som en viktig utmaning i operationssalar på sjukhus. För patienter som genomgår kirurgi finns alltid en risk att de efter ingreppet utvecklar någon behandlingsrelaterad komplikation.

Allmänt accepterat är att de luftburna bakterier som når operationsområdet huvudsakligen består av stafylokocker frigjorda från hudfloran av operationspersonalen i operationssalen, och att endast en liten del av dessa partiklar behövs för att initiera en allvarlig infektion i det behandlade området. Sårinfektioner innebär inte bara en enorm börda för hälso- och sjukvårdsresurser, utan utgör också en betydande risk för patienten. På sjukhus förvärvad infektion finns bland de främsta dödsorsakerna i kirurgiska patientgrupper.. En bred kunskap och förståelse av spridningsmekanismer och källor till infektionsspridande partiklar kan ge värdefulla möjligheter att kontrollera och minimera postoperativa infektioner. Denna avhandling bidrar till lösningar genom analys av en rad olika ventilationssystem tillsammans med undersökning av andra faktörer som kan påverka infektionsspridningen på sjukhus, främst i operationssalar.

Syftet med arbetet är att med hjälp av CFD-teknik (Computational Fluid Dynamics) få bättre förståelse för olika luftspridningsmekanismers betydelse vid ventilation av operationssalar och vårdinrättningar på sjukhus, så att halten av bacteriebärande partiklar i luften kan minskas samtidigt som termisk komfort och luftkvalité förbättras.

 Flera luftflödesprinciper för ventilation inklusive omblandade strömning, riktad (laminär) strömning och hybridstrategier har studerats. Simuleringar av luft-, partikel- och spårgasflöden gjordes för alla fallstudier för att undersöka partikelevakuering och luftomsättning i rummet. Flera viktiga parametrar som påverkar detta undersöktes och relevanta förbättringar  föreslås i samarbete med industrin.

Av resultaten framgår att mängden genererade bakterier i en operationssal  kan begränsas genom att minska antalet personer i operationsteamet. Infektionsbenägna operationer skall utföras med så lite personal som möjligt.

Den initiala källstyrkan (mängden kolonibildande enheter som en person avger per tidsenhet) från operationsteamet kan avsevärt minskas om högskyddande kläder används.

Av resultaten framgår också att ett horisontellt (laminärt) luftflöde kan vara ett bra alternativ till det ofta använda vertikala luftflödet. Ett horisontellt luftflöde är mindre känsligt för termisk påverkan från omgivningen, enkelt att installera och underhålla, relativt kostnadseffektivt och kräver vanligen ingen förändring av befintlig belysningsarmatur. Framför allt begränsar inte denna ventilationsprincip kirurgernas rörelsemönster. De kan luta kroppen över operationsområdet utan att hindra luftflödet. En flyttbar flexibel skärm för horisontell spridning av ultraren ventilationsluft i tillägg till ordinarie ventilation undersöktes också. Man fann att denna typ av tilläggsventilation kan minska antalet luftburna partiklar som bär mikroorganismer om operationspersonalen följer en strikt arbetsordning.

Bra samarbete och förståelse mellan ventilationsexperter och operationsteamet på sjukhuset är nyckeln till att få ner infektionsfrekvensen. Det är också viktigt med effektiva och frekventa utvarderingar av bakteriehalten i luften, för såväl nya  som befintliga ventilationssystem.

Place, publisher, year, edition, pages
Stockhomlm: KTH Royal Institute of Technology, 2016. , 74 p.
Series
TRITA-STKL, 2015:01
Keyword [en]
Computational Fluid Dynamics (CFD), Ventilation System, Hospital Operating Room, Bacteria Carrying Particle, Surgical Site Infection, Colony Forming Unit, Airborne Particle Control, Air Quality, Thermal Comfort, Active-Passive Air Sampling methods
Keyword [sv]
Computational Fluid Dynamics (CFD), ventilationssystem, operationssal på sjukhus, bakteriebärande partikel, infektion i samband med operation, kolonibildande enhet, kontroll av luftburna partiklar, luftkvalitet, termisk komfort, aktiva-passiva provtagningsmetoder för luft
National Category
Mechanical Engineering Environmental Engineering Architecture
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-181053ISBN: 978-91-7595-810-1 (print)OAI: oai:DiVA.org:kth-181053DiVA: diva2:898749
Public defence
2016-02-22, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20160129

Available from: 2016-01-29 Created: 2016-01-27 Last updated: 2016-02-17Bibliographically approved
List of papers
1. Influence of staff number and internal constellation on surgical site infection in an operating room
Open this publication in new window or tab >>Influence of staff number and internal constellation on surgical site infection in an operating room
2014 (English)In: Particuology, ISSN 1674-2001, E-ISSN 2210-4291, Vol. 13, no 1, 42-51 p.Article in journal (Refereed) Published
Abstract [en]

Prediction of bacteria-carrying particle (BCP) dispersion and particle distribution released from staff members in an operating room (OR) is very important for creating and sustaining a safe indoor environment. Postoperative wound infections cause significant morbidity and mortality, and contribute to increased hospitalization time. Increasing the number of personnel within the OR disrupts the ventilation airflow pattern and causes enhanced contamination risk in the area of an open wound. Whether the amount of staff within the OR influences the BCP distribution in the surgical zone has rarely been investigated. This study was conducted to explore the influence of the number of personnel in the OR on the airflow field and the BCP distribution. This was performed by applying a numerical calculation to map the airflow field and Lagrangian particle tracking (LPT) for the BCP phase. The results are reported both for active sampling and passive monitoring approaches. Not surprisingly, a growing trend in the BCP concentration (cfu/m(3)) was observed as the amount of staff in the OR increased. Passive sampling shows unpredictable results due to the sedimentation rate, especially for small particles (5-10 mu m). Risk factors for surgical site infections (SSIs) must be well understood to develop more effective prevention programs.

Keyword
Air quality, Surgical site infection, Airborne particle control, Hospital operating room, Ventilation system
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-147065 (URN)10.1016/j.partic.2013.10.006 (DOI)000336114500004 ()2-s2.0-84899485124 (Scopus ID)
Note

QC 20140624

Available from: 2014-06-24 Created: 2014-06-23 Last updated: 2017-12-05Bibliographically approved
2. A numerical investigation of vertical and horizontal laminar airflow ventilation in an operating room
Open this publication in new window or tab >>A numerical investigation of vertical and horizontal laminar airflow ventilation in an operating room
2014 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 82, 517-525 p.Article in journal (Refereed) Published
Abstract [en]

The effectiveness of vertical and horizontal ventilation systems in terms of reducing sedimentation and distribution of bacteria-carrying particles in an operating room is investigated. The exploration is carried out numerically using computational fluid dynamics. Both airborne particle concentration and sedimentation are simulated under different ventilation flow conditions. Model validation is performed through comparisons with experimental data from the literature. Achieved results reveal that the preferred selection between vertical and horizontal ventilation scenario in an operating room is highly depend on internal constellation of obstacles, work practice and supply airflow rate. Improper positioning of operating room personnel may remarkably reduce the ventilation efficiency. Increasing the airflow rate reduces particle concentration in the surgical zone. Efficient ventilation, however, is not only a matter of increasing airflow rate. Inappropriate airflow rates result in flow pattern transition from laminar to less efficient turbulent mixing. A laminar and well-organized (unidirectional) flow pattern is retired for a good result. Innovative further solutions are suggested to be found in cross-disciplinary collaboration.

Keyword
Vertical-horizontal LAF ventilation system, Bacteria-carrying particle, Hospital operating room, Air quality, Active-passive air sampling, Colony-forming unit
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-160081 (URN)10.1016/j.buildenv.2014.09.013 (DOI)000346543500049 ()2-s2.0-84908128681 (Scopus ID)
Note

QC 20150225

Available from: 2015-02-25 Created: 2015-02-13 Last updated: 2017-12-04Bibliographically approved
3. Effect of a portable ultra-clean exponential airflow unit on the particle distribution in an operating room
Open this publication in new window or tab >>Effect of a portable ultra-clean exponential airflow unit on the particle distribution in an operating room
2015 (English)In: Particuology, ISSN 1674-2001, E-ISSN 2210-4291, Vol. 18, 170-178 p.Article in journal (Refereed) Published
Abstract [en]

The effects of a mobile laminar airflow unit on the concentration, deposition and distribution of bacteria-carrying particles in an operating room are investigated. The exploration is carried out using numerical calculation schemes (computational fluid dynamics approach). The model validation was performed through result comparisons with published measurement data from literature. Two types of mobile screen units were evaluated as an extension of turbulent-mixing operating-room ventilation. Airborne particle concentration/sedimentation was recorded with and without a screen unit on the operating table and two instrument tables. Both active and passive air sampling were examined and the results are compared. It was found that the additional mobile ultra-clean laminar airflow unit reduces the counts of airborne bacteria and surface contamination to a level acceptable for infection-prone surgeries.

Keyword
Computational fluid dynamics, Bacteria-carrying particle, Surgical-site infection, Hospital operating room, Air quality, Active-passive air sampling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-162970 (URN)10.1016/j.partic.2014.06.002 (DOI)000349730200020 ()2-s2.0-84922815866 (Scopus ID)
Note

QC 20150331

Available from: 2015-03-31 Created: 2015-03-26 Last updated: 2017-12-04Bibliographically approved
4. Surgical clothing systems in laminar airflow operating room: A numerical assessment
Open this publication in new window or tab >>Surgical clothing systems in laminar airflow operating room: A numerical assessment
2014 (English)In: Journal of Infection and Public Health, ISSN 1876-0341, Vol. 7, no 6, 508-516 p.Article in journal (Refereed) Published
Abstract [en]

This study compared two different laminar airflow distribution strategies - horizontal and vertical - and investigated the effectiveness of both ventilation systems in terms of reducing the sedimentation and distribution of bacteria-carrying particles. Three different staff clothing systems, which resulted in source strengths of 1.5, 4 and 5 CFU/s per person, were considered. The exploration was conducted numerically using a computational fluid dynamics technique. Active and passive air sampling methods were simulated in addition to recovery tests, and the results were compared. Model validation was performed through comparisons with measurement data from the published literature. The recovery test yielded a value of 8.1 min for the horizontal ventilation scenario and 11.9 min for the vertical ventilation system. Fewer particles were captured by the slit sampler and in sedimentation areas with the horizontal ventilation system. The simulated results revealed that under identical conditions in the examined operating room, the horizontal laminar ventilation system performed better than the vertical option. The internal constellation of lamps, the surgical team and objects could have a serious effect on the movement of infectious particles and therefore on postoperative surgical site infections.

Keyword
Active-passive air sampling, Bacteria-carrying particle, Colony-forming unit, Computational fluid dynamics, Operating room, Surgical site infection
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-161780 (URN)10.1016/j.jiph.2014.07.011 (DOI)000354964200007 ()25155072 (PubMedID)2-s2.0-84911001560 (Scopus ID)
Note

QC 20150317

Available from: 2015-03-17 Created: 2015-03-17 Last updated: 2016-01-29Bibliographically approved
5. Three distinct surgical clothing systems in a turbulent mixing operating room equipped with mobile ultraclean laminar airflow screen: A numerical evaluation
Open this publication in new window or tab >>Three distinct surgical clothing systems in a turbulent mixing operating room equipped with mobile ultraclean laminar airflow screen: A numerical evaluation
2016 (English)In: Science and Technology for the Built Environment, ISSN 2374-4731Article in journal (Refereed) Published
Abstract [en]

Two types of mobile screens producing ultraclean local laminar airflow were investigated as an addition to turbulent mixing operating room ventilation. The exploration was carried out numerically using computational fluid dynamics. Surface and volumetric particle counts were simulated on the operating and instrument tables with and without the additional mobile airflow screen. Three different source strengths (the mean bacteria-carrying particle value emitted from one person per second) due to staff clothing variety were considered. Model validation was performed through result comparisons with experimental data from the literature. Results confirmed that the mobile screen units reduced the airborne bacteria to an acceptable level for infection-prone surgeries. No significant particle concentration differences existed in the periphery of the operating room. Lower source strength resulting from a clothing system with high protective capacity reduced particle concentration.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
National Category
Mechanical Engineering Medical Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-181055 (URN)10.1080/23744731.2015.1113838 (DOI)000375862900010 ()
Note

QC 20160127

Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2016-06-03Bibliographically approved
6. Thermal comfort of the surgical staff in an operating theatre: a numerical study on laminar and mixing ventilation systems
Open this publication in new window or tab >>Thermal comfort of the surgical staff in an operating theatre: a numerical study on laminar and mixing ventilation systems
2016 (English)In: Proceeding  the 14th international conference of indoor air quality and climate (Ghent, Belgium July 3-8 2016), 2016Conference paper, Published paper (Refereed)
National Category
Medical Engineering Medical Engineering
Identifiers
urn:nbn:se:kth:diva-181054 (URN)
Conference
Indoor Air 2016
Note

NQC 201601

Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2016-02-22Bibliographically approved

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