Air handling in intensive care units

[John Ferguson]

Dear All

Our ICU for some time has been on a full exhaust mode – this came about at the time when we faced up to an ongoing MRAB outbreak. We had some evidence (not strong) that the ventilation system might have played a role.

However this process is wasteful, particularly in the summer and it makes control of humidity very tricky – some days , we cannot bring the humidity below 80% given the grunt within the air con system

I would be interested to know :

a) What sort of ventilation is used in your ICU

b) Do you recirculate air?

c) Is it filtered prior to recirculation? If so how filtered?

d) What humidity levels do you experience in the icu through the year?

Thanks !

Kind regards
John

Dr John Ferguson
Director, IPC, Hunter New England Health
Infectious Diseases & Microbiology
+61 428 885573

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[Michael Wishart]

Hi John

Below in the reply from our facilities manager. We don’t tend to have problems with humidity in our 16 bed unit, depsite being in Brisbane

Michael

The ICU runs with a normal minimum fresh air setting of approx. 40%

The system has got Temp & humidity control with terminal HEPAs in all the patient areas

There is an automatic economy cycle that increases the fresh air & starts a variable speed extract fan.

The economy cycle is based on the external enthalpy(combined temperature & humidity) being lower than the room set point.

Both the damper & fan speed are auto adjusted to minimise chilled water use for cooling & de-humidification.

There are also two negative pressure rooms with a proper air lock however this is used as a store & staff enter the rooms directly off the main ICU

Michael Wishart
Infection Control Coordinator
Holy Spirit Northside Private Hospital
627 Rode Road, Chermside, Qld 4032
t: (07) 3326 3068 | f: (07) 3326 3523
e: Michael.Wishart@hsn.org.au
w:www.holyspiritnorthside.org.au
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Dear All

Our ICU for some time has been on a full exhaust mode this came about at the time when we faced up to an ongoing MRAB outbreak. We had some evidence (not strong) that the ventilation system might have played a role.

However this process is wasteful, particularly in the summer and it makes control of humidity very tricky some days , we cannot bring the humidity below 80% given the grunt within the air con system

I would be interested to know :

a) What sort of ventilation is used in your ICU

b) Do you recirculate air?

c) Is it filtered prior to recirculation? If so how filtered?

d) What humidity levels do you experience in the icu through the year?

Thanks !

Kind regards
John

Dr John Ferguson
Director, IPC, Hunter New England Health
Infectious Diseases & Microbiology
+61 428 885573

MESSAGES POSTED TO THIS LIST ARE SOLELY THE OPINION OF THE AUTHOR, AND DO NOT REPRESENT THE OPINION OF ACIPC.

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[Thomson, Rachel EA]

Hi John,

I forwarded these questions to our guru engineering people and received the following reply. I have included the initial preamble too as I think these comments are relevant to the overall answers.

Kind regards
Rachel

Rachel Thomson

Nurse Unit Manager
Infection Prevention & Control Unit
Royal Hobart Hospital
E: rachel.thomson@dhhs.tas.gov.au

To give an accurate understanding of how the mechanical systems work in our ICU it is important to understand that there is on old section and a new infill section, both of which have new (but separate) plant. There are several (6 off) units that serve both areas. This does not include the isolation room, which really is a separate item.

I’ll start by qualifying that Hobart’s ambient conditions are fairly different from NSW, not just in temperature, but in humidity. When we have warmer conditions, we are usually very dry (10-50% RH). In winter we also experience low RH, unless it’s raining. We therefore rarely require dehumidification and don’t design for it.

Another thing to note is that Tasmania has ideal ambient conditions for economy cycle, the practice of using 100% outdoor air (OA) if it is between 13-18C when the system calls for cooling.

For the old ICU ward (and offices, waiting, reception, etc.) and the new ICU bed bays we are running air to air heat exchangers on a 100% outdoor air system. Each zone has its own exhaust system, which balances the system so as to not recirculate the bed bay air into the general communal spaces.

These units contain heat exchanges (HX) to counter the less efficient practice of utilising 100% OA, and the HX is packaged into a single, larger, unit with the fan and associated heating and cooling coils. These systems contain in duct steam humidifiers to give more moisture to the supply air, when required (most of the time).

The new ICU corridor, write-up room, office, pharmacy, sterile store and equipment rooms are serviced by a multi zone, common return air handling unit. It uses the multi zone unit to achieve better internal thermal comfort with different thermal profiles. This unit also utilises economy cycle if the conditions are correct.

All of the units supplying the new and old ICU areas have the following filtration:

Pre-filter on OA and exhaust air; Grade G4;

Deep bed supply air filter: Grade F8;

And to the sterile store, a terminal HEPA filter (Grade H13 from memory).

Hopefully this helps answer John’s queries:

What sort of ventilation is used in your ICU? Multiple Air Handling Units, mostly 100% OA.

Do you recirculate air? Only for a small percentage of the areas.

Is it filtered prior to recirculation? If so how filtered? Yes, pre-filter and deep bed, plus local HEPA where required.

What humidity levels do you experience in the ICU through the year? Relatively dry, so humidification is required.

Kind regards

Scott Ellis
Facilities Assets & Projects Officer
Facilities & Engineering
Tasmanian Health Organisation – South

Dear All

Our ICU for some time has been on a full exhaust mode – this came about at the time when we faced up to an ongoing MRAB outbreak. We had some evidence (not strong) that the ventilation system might have played a role.

However this process is wasteful, particularly in the summer and it makes control of humidity very tricky – some days , we cannot bring the humidity below 80% given the grunt within the air con system

I would be interested to know :

a) What sort of ventilation is used in your ICU

b) Do you recirculate air?

c) Is it filtered prior to recirculation? If so how filtered?

d) What humidity levels do you experience in the icu through the year?

Thanks !

Kind regards
John

Dr John Ferguson
Director, IPC, Hunter New England Health
Infectious Diseases & Microbiology
+61 428 885573

MESSAGES POSTED TO THIS LIST ARE SOLELY THE OPINION OF THE AUTHOR, AND DO NOT REPRESENT THE OPINION OF ACIPC.

The use of trade/product/commercial brand names through the list is discouraged by ACIPC. If you wish to discuss specific reference to products or services by brand or commercial names, please do this outside the list.

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