Since 1965 an awareness as to contaminated ventilating machines
causing infections to subsequent patients has resulted in a
universal acceptance to use filters to protect the patients, staff
and machinery. Filters and Heat Moisture Exchangers (HME) have
developed since then not only to prevent bacterial and viral
contamination but to also compensate for bypassing the upper airway
during anaesthesia or intubation.
The blood born virus advisory panel of the Association of
Anaesthetists of Great Britain and Ireland recommended that an
appropriate filter should be placed between the patient and the
breathing system, with a new filter being used for each patient.
This protection may be achieved by two different filtration
methods, either by mechanical filtration, or by electrostatic
charge filtration.
Mechanical filters, also known as pleated paper filters, have a
tightly packed medium with a hydrophobic coating providing a small
pore size membrane that physically stops the passage of organisms.
Typically these filters have very high levels of efficiency and
their hydrophobic properties also provide a degree of
humidification for the patient. Electrostatic filters use a medium
that is loosely woven and given a charge that holds onto
micro-organisms allowing filtration in a small, light casing.
Properties of Filters and
HMEF's
When considering filters a number of important properties should
be taken in to account and these are:
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1. Filtration
Efficiency
As many as 10-15% of intubated patients develop pneumonia at a
level of 1-3% per day of intubation. These pneumonia's may prolong
hospital stays by 4-9 days and contribute to as many as 15% of all
hospital deaths.
From this it is evident that filtration efficiency is paramount to
protect the patients and ventilators from cross contamination.
Flexicare filters provide protection against bacteria and viruses
at a very high level of efficiency. This level of effectiveness is
independently tested and verified by the Applied Centre for
Microbiology and Research at Porton Down Salisbury, giving
confidence in our filter properties. Flexicare filters will
maintain the specified level of efficiency for the full recommended
period of use.
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3. Humidification
Abilities
To counteract the risk of actelectasis, epithelial damage
and reduction of mucocillary transport, adequate humidification
should be provided to long term intubated patients. HMEF's may not
only act against these factors by providing humidification, their
use is also thought to reduce the incidence of late onset
Ventilator Associated Pneumonia compared to heated wire
systems.
It is recommended that HMEF humidification levels should be at
least 30mg/L H2O at an inspired air temperature of 30oC. All
Flexicare HMEF's exceed this minimum by providing a maximum
moisture output performance of 32.3mg/L H2O as independently tested
and verified by the Medical Device Agency (MDA).
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2. Light Weight
and Ergonomically Shaped
Flexicare Filters and HMEF's designs provide a rounded ergonomic
shape to prevent pressure marking or discomfort for the patient.
They are of light weight design thus reducing drag on breathing
systems and are made of clear material allowing visual observation
in terms of potential obstructions. |
4. Minimal Dead
Space and Minimal Pressure Drop
Design of the filter housing must provide the smallest dead space
possible whilst at the same time allowing a good gas flow with
minimal resistance (pressure drop) through the filter media. The
design of Flexicare Filters and HMEF's has incorporated a balance
of these critical requirements to create a filter with minimal
resistance to flow while maintaining a low dead space. |