natural ventilation of health care facilities · natural ventilation general building design •...
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Natural Natural VentilationVentilation of Health Care of Health Care FacilitiesFacilities
HOSPITAL NACIONAL
“DOS DE MAYO”
Dr Rod Escombe MD DTM&H PhDHonorary Research Fellow, Wellcome Centre for Clinical Tropical Medicine & Department of Infectious Diseases & Immunity, Imperial College London, UK.Senior Investigator, Asociación Benéfica PRISMA, Lima, Perú. GP Registrar, St Mary’s Hospital, London, UK.
Engineering Methods for the Control of Airborne Infections: An International Perspective
Harvard School of Public Health20th July 2008
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1.Bonifacio N. Emerg Inf Dis 2002;8:747 2.Joshi R. PLoS Med 2006; 3:494 3.Drobniewski F. PLoS Med 2007; 4:55
MDR, XDRHIV-TB
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• Dilutional ventilation is the mainstay of environmental control measures for airborne infections
• Aim to reduce the concentration of infectious airborne particles
• Reduce exposure of patients, staff and visitors
Ventilation and control of airborne Ventilation and control of airborne infection in health care facilitiesinfection in health care facilities
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0
20
40
60
80
100
0 1 2 3 4
Time (hours)
Con
cent
ratio
n (c
fu/m
3 )
1 ACH2
48
Measuring ventilation: Measuring ventilation: Air Changes per Hour (ACH)Air Changes per Hour (ACH)
Effect of ACH on concentration of airborne particles
Freshair
=
33:67%
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Wells-Riley equation:
C=S(1-e –Iqpt/Q)
C= new cases S=susceptiblesI =number of infectors q=infectious quanta produced per hourp=pulmonary minute ventilationt=duration of exposureQ=absolute ventilation (= ACH x room volume)
Modelling Modelling effect of ventilation on effect of ventilation on airborne infectionairborne infection
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Effect of dilutional ventilation on risk of Effect of dilutional ventilation on risk of airborne infectionairborne infection
Ventilation rate (h-1)
0 10 20 30Quanta
generation (quanta/m
in)
0
10
20
Risk
0
0.5
1
Yuguo Li
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MechanicalMechanical ventilationventilation
• Air changes diluteinfectious particles
• Negative pressure
• Standard of care
CDC Guidelines 2005: 6-12 ACH for high-risk areas
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Natural ventilationNatural ventilation
• Passive supply of outdoor air to a building interior for ventilation and cooling
• Historically all buildings employed natural ventilation
Pantheon, Rome – 120 AD
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Natural ventilation in health care facilities
“The very first canon of nursing, the first and the last thing upon which a nurse’s attention must be fixed, the first essential to the patient, without which all the rest you can do for him is as nothing, with which I had almost said you may leave all the rest alone, is this: to keep the air he breathes as pure as the external air, without chilling him”
Notes on Nursing – What it is and what it is not. 1860. London
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TB sanatoriaTB sanatoria• Pre-antibiotic era• Fresh air therapy
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Midhurst, Sussex, UK
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With modern building design, advent of HVAC, natural ventilation fell from favour
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Renewed interest in Renewed interest in natural ventilationnatural ventilation
General building design• Need to reduce energy costs: “green buildings”
Health care facilities• TB & HIV epidemics, emergence of drug
resistance and recognition of nosocomial spread1
• TB prevention low resource settings. WHO 19992
• TB Infection control in era of HIV. WHO 20073
• Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care. WHO Interim guidelines 20074
Evidence base so far is slim
• Data from Peru
1. Gandhi, N.R., et al. XDR-TB in South Africa. Lancet, 2006. 368:1575-80. 2. http://www.who.int/docstore/gtb/publications/healthcare/PDF/WHO99-269.pdf3. http://whqlibdoc.who.int/hq/1999/WHO_TB_99.269_ADD_eng.pdf4. http://www.who.int/csr/resources/publications/WHO_CD_EPR_2007_6/en/
World Health Organization
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Natural ventilationNatural ventilation
• Simply opening windows• Low cost• Maintenance free• Climate dependant
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Natural ventilation Natural ventilation –– basic principlesbasic principles
Cross ventilation Stack effect
Hot air rises
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Natural ventilationNatural ventilation –– basic principlesbasic principles
Poor Improved
Layout
WHO guidelines
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Martin Yag
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Paul Jensen
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Natural ventilation in Lima hospitalsNatural ventilation in Lima hospitals• 8 hospitals
– 5 old-fashioned design built pre-1950– 3 modern hospitals built 1970-90
• 70 naturally ventilated rooms
– Respiratory isolation rooms– TB, respiratory, infectious disease, HIV, general medical wards– Emergency departments– Out-patient clinics and waiting rooms
• 12 mechanically ventilated respiratory isolation rooms
– Built in 2000, renovated by Wellcome Trust in 2004