Nuts
and bolts of hyperbaric oxygen therapy
Hyperbaric
oxygen therapy
consists of breathing 100% oxygen while
inside a therapy chamber. The chamber is compressed to a pressure
higher than you are breathing now and can increase oxygen levels in
your body up to 15 times.
Hyperbaric chambers range in size and operational principles. Smaller
units provide individualized therapy whereas larger hospital settings
can treat a dozen or more patients simultaneously.
There are two ways of increasing the pressure inside a
hyperbaric chamber.
Oxygen
flow-through
chambers
Compressing a hyperbaric chamber with pure medical grade oxygen
provides the most efficient, safe and comfortable treatment. Oxygen
flows through the chamber at a rate of up to 500 liters/min.
Continuously replenishing the inside atmosphere assures a clean oxygen
environment with a well controlled temperature.
Oxygen is absorbed
through both lungs and skin for maximum therapy efficiency. This can
reduce the overall number of therapy sessions required.
The most
comfortable oxygen flow-through chambers are made of special clear
acrylic
glass allowing full view of your surroundings. These are ideal for
people having issues with
confinement anxiety.
In an oxygen flow-through chamber nitrogen does not present a risk of
decompression sickness when the therapy ends.
Air compressed
chambers
Alternatively, the chamber can be compressed with air and oxygen is
inhaled through a mask or a hood.
Oxygen is now absorbed almost
exclusively through the lungs while the skin is exposed to excessive
high concentrations of nitrogen.
The “oxygen therapy” does not start
until the mask or hood is applied with a sufficient oxygen flow
(>15 l/min).
Breathing compressed air inside the chamber exposes the patient to
undesirably high concentrations of nitrogen effectively diluting the
oxygen therapy (
ref). This makes the air filled
chambers less efficient than the oxygen chambers.
The total therapy time is therefore usually longer and more sessions
are needed to achieve results comparable to the oxygen chamber.
Air compressed chambers come in a variety of sizes and shapes with
larger “multiplace” chambers being the hospital standard.
They allow for specially trained health care professionals to attend
patients inside the chamber.
As the air inside the chamber is compressed the environment
becomes warm and humid with a potential risk of bacterial buildup and
patient cross contamination.
This mandates strict chamber cleaning procedures and careful screening
of the patients.
Reducing the air pressure at the end of therapy has to be done
carefully to minimize the risk of developing decompression sickness.
Comparing
therapy options
Three factors determine the efficiency of oxygen therapy:
- Duration
of oxygen exposure
- Pressure
and gasmixture inside the chamber
- Frequency
of therapy
Research in hyperbaric medicine is generally performed with
90
min of oxygen exposure at pressures ranging from
2.0
to 3.0 atmosphere
(ATA) or 27 to 41 psi. Therapeutic
momentum is maintained with
daily
sessions.
There are several different
styles of hyperbaric chamber technologies. They are listed below from
low to high maximum operating pressure:
Topical chambers:
An acrylic box with an opening for an arm or a leg to extend
into
a pressurized chamber. A tight rubber seal around the
extremity
allows the box to maintain a very modest increase in pressure inside.
The box is filled with oxygen or
oxygen enriched air however the maximum pressure is limited by the
constricting body seal. Unfortunately this reduces blood
flow to the limb thereby counteracting the therapeutic effect of the
therapy.
Typically
the maximum pressure is less than 1 psi above
standard
atmospheric pressure making it a total of only 1.07 ATA. As
implied by the name a “topical” chamber only exposes the
surface
of the skin to oxygen. This severely limits the amount oxygen
that can be delivered to the body. Furthermore a dry wound surface is
fairly impermeable to oxygen thus rendering the therapy even less
efficient.
Inflatable bag:
This technology
found its way from mountaineering sports where it was used for sleeping
at altitudes in close to normal oxygen conditions to prevent altitude
sickness. Among hyperbaricists it is called “mild
hyperbaric”, given its limitations in treatment pressure.
It is compressed with air
or
oxygen enriched air with maximum pressure limited by fabric and closing
device - typically 2 to 3 psi above standard atmospheric pressure (~1.2
ATA).
Having such low operating pressure, bags currently do not have
to comply with certification requirements by PVHO standards (Pressure
Vessel for Human Occupancy) and can be used in small scale offices and
homes, provided that the operators have obtained proper
knowledge to safely operate pressurized equipment designed for therapy
Air compressed chambers -
monoplace are designed for single person breathing
oxygen from a mask or
a hood. The chamber wall is steel with port windows for
external
view and can either have a cockpit style reclined seat
or a stretcher for laying down completely.
The operating
pressure
is typically limited to less
than 14.7
psi above standard atmospheric pressure (2 ATA).
Some air compressed
chamber types carrying a
Health
Canada Medical Device License can reach pressures up
to 3 ATA. Those will have to comply with
certification requirements by
PVHO
standards (Pressure Vessel for Human Occupancy).
Oxygen is inhaled through a mask or a hood with a neck seal and the
therapy time counts only
during oxygen breathing. See more below.
Operators have to be trained and certified as hyperbaric technicians
(CHT).
Oxygen compressed
chambers - monoplace
are designed for full oxygen exposure of one person.
These chambers are
typically made
of large clear double cylinders Plexiglass tubes allowing full in and
outside view.
The operating pressure is limited to 3 ATA or
29.4
psi
above atmospheric pressure as safe and efficient maximum oxygen
exposure.
The chamber requires chamber certification according
to
PVHO
standards (Pressure Vessel for Human Occupancy) as well
as
Health
Canada Medical Device License.
These chambers offers the most efficient oxygen therapy by delivering
oxygen systemically
through the lungs
and through the
skin. In comparison, therapy in air
compressed chamber will exposed the skin to high concentration of
nitrogen
given its 80-20 percentage ratio of nitrogen and oxygen (
ref).
Multiplaced air
compressed chambers
are designed for simultaneous treatment of groups of people
breathing oxygen from masks or hoods. These chambers are
usually
situated within hospital
settings because of their operating economy and need for internal
operators, usually doctors or nurses trained in hyperbaric medicine.
Furthermore, a multiplace chamber requires fairly large scale
external support systems, such as
storage of emergency air banks (supply), compressors, backup systems,
etc. as well as standby operators, external technicians and medical
personnel.
A
multiplace chamber typically has the capability to reach pressures
beyond up to 6 ATA for acute treatment of decompression sickness in
divers.
This requires the chambers to comply with strict safety guidelines by
PVHO
standards (Pressure Vessel for Human Occupancy) as well
as
Health
Canada Medical Device License.
Given
that multiple people share a relatively confined space these chambers
require careful cleaning procedures and patient screening to minimize
risk of cross contamination of infectious diseases.
Air
vs.
oxygen compressed chamber
Oxygen
flow-through
chambers
Oxygen
compressed chambers are both the most effective and safest
hyperbaric chamber technology available for two reasons:
- The
only external gas source for oxygen compressed chambers is oxygen and
as such it maximizes the
potential absorption of oxygen. Exposing both lungs and skin
to oxygen provides the fastest and most
efficient way of increasing oxygen concentration in the body (ref).
- By virtue of its operating principal oxygen
compressed chambers eliminates exposure to gases other than oxygen.
Nitrogen exposure is a concern in air filled chambers where additional
nitrogen increases the risk of developing decompression sickness at
the end of the therapy especially if the chamber pressure is reduced
too rapidly.
In contrast, the oxygen compressed chamber will decrease the nitrogen
concentration in the body and therefore allow for a safe decompression
at any rate and any time during the therapy.
Air compressed
chambers
As
indicated above there are other significant differences affecting
the choice of hyperbaric chamber.
- Air compressed chambers will have a hot and humid inside
atmosphere
during compression and will require thorough disinfection procedures to
minimize risk of patient cross contamination. In contrast the
oxygen compressed chamber will annihilate anaerobic bacterias inside
the chamber during every therapy, to some degree a "self cleaning"
process.
- Therapy sessions in air filled chambers are
longer (approximately 2 hours) to include non-oxygen breathing periods
during compression and decompression. They may also require
more
sessions to obtain results similar to those achieved with the oxygen
compressed chamber.
- Air compressed chambers minimizes the use of
oxygen but are, however, mechanically more complex given the
requirement of
external air compressors, backup units, air storage and safety
systems.
Furthermore, it is crucial for air compressed chamber
installations to have a
clean air supply and oil-free compressors with a reliable power source
to deliver the
pressure. Any pollutant in the air intake will be magnified
by
the higher pressure inside the chamber.
- By contrast, the oxygen filled chambers constantly
ventilate the inside
atmosphere with pure oxygen and will continue to do so regardless of
electrical power failures. The chamber remains operational
as long as the oxygen source maintains a pipline pressure.
Buyers beware
When looking for hyperbaric services ask questions about equipment
certifications, treatment protocols and personnel training.
- Health
Canada requires a Medical Device License on all
therapeutic equipment
imported and distributed in Canada. Very few
chamber types are
approved
(see www.mdall.ca
and search for Device Name: hyperbaric chamber)
- Local safety authorities will
require Operational
Licenses to be issue for individual chambers and facility
installations.
It is mandatory to have Operational Licenses on display at the
facility similar to any applicable business licenses.
- Academically accepted treatment
pressure ranges from 2 to 3
atmosphere of pure oxygen.
Small soft-shell inflatable bags marketed as “hyperbaric chambers” or
"mild hyperbaric" are
generally not capable of reaching therapeutic pressures (a
write-up on why these bags don't fit in the category of
hyperbaric oxygen therapy.)
- Therapy
time counts only during oxygen exposure.
Breathing air under
pressure will dilute the effect of oxygen and increase the amount of
absorbed nitrogen.
- Effective therapy requires daily
sessions to initiate the
body’s own healing response.
