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Covid Air Management System For Reducing Transmission of Covid-19 in Hospitals
CAMS, previously known as Air Dynamics Management, ADM
The current pandemic of Covid-19 is mainly spread by inhaling
droplets from infected people who are within two metres or less, and to some
extent by aerosols of virus particles, which may persist in air for 30 minutes
or more.
Several studies have shown that a significant number of Covid-19 cases were
acquired in hospital.
This paper looks at a way in which the hospital route of transmission
may be significantly reduced.
The transmission risk from Covid-19 cases
People in hospitals who are known to be infected with
Covid-19 are putting out droplets containing the Sars-CoV-2 constantly and in
large amounts when they cough and speak, especially in the first week since
symptoms began.
The exhaled air from patients on respirators and CPAP is not
a problem, as their air is usually or always in a closed circuit, but milder
Covid-19 cases who are receiving oxygen delivered via nasal cannula or mask
will be continually exhaling droplets into the hospital environment. The air in
their vicinity and in their room will contain a considerable quantity of virus,
both as droplets and as aerosols.
Bed coverings and the floor within a couple of metres will be
hosting significant amounts of virus. This virus will feed back onto the
patient, continually re-infecting them every time they breathe in, or when they
touch their face after letting their hands rest on their sheets. The floors can
be cleansed at frequent intervals, but the bed linen presents an infection risk
to anyone who handles it.
The air in the vicinity of the patient poses a health and
safety risk to anyone who enters the room or indeed breathes air in the
vicinity of the room. PPE is used to reduce this risk, but PPE does not present
an impenetrable shield, and 649 healthcare workers (including 36 doctors) have
died from Covid-19 contracted while giving care.
Systems to manage expired air
The above source of potential infection will be reduced significantly
if all the exhaled breath from a Covid-19 sufferer is withdrawn and sterilised.
It may be the case that in some hospitals air from the
general vicinity of the patient is already “scavenged” by an induction tube
located at a distance from the patient, but this will not produce 100% capture
of droplets.
The simplest way to capture expired air is by means of a
hood positioned over the head. Air will be withdrawn from the hood through a
tube positioned above the head at a rate in the region of 6 litres/minute that
will prevent any expired air from escaping. The material of the hood will be of
transparent plastic that can be sterilised. This hood will produce an upward
flow of air across the face, and all expired air will be safely collected. See
Fig 1 below.
Figure 1 – Air Management Hood (see on foot of this post)
Simple mask with exhaust tube
A mask may be used instead of a hood. It will be provided
with and input and output tube. This means that much of the oxygen supplied
will pass immediately into the exhaust air system, rather than passing into the
air in the vicinity of the patient.
Mask with alternating flow
In another embodiment the mask may be designed so that
oxygen is supplied when the patients are in the inspiratory stage of their
respiratory cycle and cut off when the patients are in the expiratory stage of
their respiratory cycle. Conversely the exhaust air duct will open with the
expiratory phase of the respiratory cycle and close when they are in the
inspiratory phase of the respiratory cycle.
This reciprocating flow may be produced by a simple valve
design that will allow the patient to adjust the rate of the delivery cycle.
The plan may be obtained from the author on request.
Assisted respiration
Alternatively, for patients with severely compromised
respiration, electrically actuated valves could be provided which would be
controlled by information from sensors sited on the patient’s chest which would
allow synchronised delivery and extraction of gases. The patient would receive useful
assistance in respiration from this arrangement. This is available as Positive
End-Expiratory Pressure (PEEP).
Management of removed air
If the hospital or nursing home has only one or two patients
with Covid-19, the air removed from the hood may simply be passed through a
HEPA filter in the patient’s room.
If there are several patients in the building, it may be
better if each tube from the Covid-19 patient will be connected to a manifold,
and the total air removed from all Covid-19 patients in a hospital (or nursing
home) will be passed through a unit that will apply effective sterilisation by
chemical means (e.g. sodium hypochlorite mist), physical means (e.g.
ultraviolet light or heat) , or a combination of both, before venting to the
atmosphere.
Many modern hospitals have a centralised (integrated) vacuum
cleaning system that might be adapted to serve as a starting point for the air
extraction ducts. The system will of course have to be modified to sterilise it
of all pathogens.
Heat exchangers may be added to minimise heat loss from the
establishment in colder months.
Using these simple technologies, hospital acquired Covid-19
infections, whether by other patients or by front-line staff, will be greatly
reduced.
Discussion
Cost
There will be a small capital cost attached to fitting these
air management tubes, fans, and sterilising facilities, but the costs will be
recouped from decreased expenditure caused by hospital acquired infections
affecting staff and even other patients.
It is possible that Government may be persuaded to subsidise
these technologies in order to help to suppress the pandemic.
Apparatus will not have to be scrapped when the Covid-19 pandemic
is over. Pandemics are arising more and more
frequently as shown in this table:
Table 1
HIV/AIDS ~1940
Ebola 1976
Sars 2002
Mers 2012
Covid-19 2019
It can be seen that the interval between emergence of new
infections is decreasing with time, and we can safely infer that new pandemics
will occur from time to time, and therefore the demand for air quality management
equipment will be sustained and increased.
Effect on the patient
Since patients are breathing and coughing out viral
particles, they will be re-infecting
themselves each time they breathe in and each time they touch their face. It is
arguably the case that ADM will reduce the viral load that their immune system
has to deal with, and therefore will aid recovery. It will be possible to test
this hypothesis by reviewing patient outcomes a few weeks after the technology
has been installed by auditing outcomes on patients treated with Covid Air Management.
Other
measures
Air Management must
be seen as one component of a systematic response. Hands, face and space must
be continued alongside air dynamics management.
Noise
Attention must be given to the problem of noise associated
with air management. Tubes will be of smooth
bore rather than corrugated. Any valves will be made of soft material, and the points
of impact of valves will be designed to avoid noise. Air flow will be laminar,
and as slow as is possible compatible with amounts required for respiration.
Safety
There is a serious responsibility undertaken in managing air
containing large amounts of Sars-CoV-2. System integrity is vital since leaks
in delivery tubes could result new infections. Potential breakdown in the
system of exhaust air management must be monitored with regular checks.
Conclusion
The advantages of the Covid emissions control system are:
- Lessened
risk of infection to front line staff - doctors, nurses, paramedics, and
cleaners - entering the C19 patient’s room
- Lessened
risk of infection in those breathing air drifting from the vicinity of C19
patients
- Lessened
stress and anxiety in front line staff
- Possible
faster recovery times for C19
patients as they will have less viral reinfection load from re-breathing
their own air and touching and ingesting virus from their bed sheets
- Less
cost to hospital from staff losses due to self-isolation and staff illness
- Less
risk of litigation from individuals who contract Covid-19 in hospital
There is a strong case, both from a public health and a
financial viewpoint, for hospital management to install Air Dynamics Management
systems for Covid-19 patients.
Richard Lawson MB BS, MRCPsych rlawson@gn.apc.org 29/09/2020
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