Oxygen: A User's Perspective
Conservers & Cannulas
The information here provided is for
educational purposes only and it is not intended nor implied to be a
substitute for professional medical advice. Always consult your own
physician or healthcare provider with any questions you may have
regarding a medical condition.
pulse-type conserver (also called a demand
oxygen delivery device (DODD)) is a device that senses the beginning of
a breath and delivers oxygen only when the user inhales. Some
conservers are battery powered (electronic
) whereas others are
powered by gas pressure ( pneumatic
). Electronic conservers use
a single lumen cannula. Pneumatic conservers require a dual lumen
Some conservers deliver oxygen on every inhalation (every-breath
conservers) whereas others may skip one, two,
or three inhalations (intermittent-breath conservers ).
Conservers designed to work only with compressed oxygen cylinders are
usually donut shaped so they fit over the neck of the cylinder.
Conservers for liquid oxygen are usually built into the tank.
The focus of this section is on conservers, wherein we try to
understand how to deal with oxygen that is metered to us in
doses. What we want from a conserver is to make our portable
system the lightest in weight, one that, like the Energizer
bunny, keeps going and going, and one that keeps us from becoming
breathless. But, I am getting ahead of myself. Let's start with the
We breathe to allow our lungs to exchange old air for new, oxygen for
carbon dioxide. Each one of us breathes more or less automatically at a
rate that is uniquely our own. The waveforms in Figure 1 show that we
inhale for about one-third of each breath (the graph above the
horizontal axis), then exhale for about two-thirds (the graph below the
Figure 1 shows, most work inhaling occurs
during the first half second of an inhalation. It would make sense that
this is the time period when supplementary
oxygen should be provided in order to be most effective. As you will
see later in this section, that is the time period
where conservers do most of their work.
Waveforms of Three Breathing Rates*
|* Assumes a lung capacity of 520
Source: Valley Inspired Products, LLC at
In this section and the one
following I will use graphs developed by Robert McCoy
and Peter Bliss of Valley Inspired Products, LLC of Burnsville, MN.
Peter Bliss graciously allowed me to modify and use the graphs that he
developed as part of his research into breathing patterns and conserver
waveforms. Whatever your connection with
oxygen therapy, you should be very grateful the work that Valley
Inspired Products has done. To see more of their work, please visit
All conservers have the
following common elements:
- Regulators are required for compressed oxygen systems.
Regulators may be separate or built into the donut shaped conserver
which fits over the cylinder's valve. Regulators have two jobs. The
first is to reduce pressure as the oxygen leaves the cylinder to a
usable 22 or 50 psi (pounds per square inch). Its second job is to set
the rate of continuous flow. The gauge on the regulator records the
amount of oxygen remaining in the cylinder. By the time the pointer on
the gauge reaches the red area, the pressure within the cylinder has
decreased to a point where the rate
of flow of oxygen maybe below your prescribed flow. For this reason,
you should replace the cylinder when the pointer enters the red area.
- Most electronic conservers have a switch that toggles
between pulse and continuous flow to set the conserver to continuous
flow when there is a conserver or battery failure.(Pneumatic conservers
automatically default to continuous flow when the conserver
malfunction.) The flow selection switch is
a two-position switch used to select between continuous and pulsating
flow. Continuous flow on most conservers is factory set to
2 Lpm. Manufacturers recommend that you keep this switch in the
pulsating flow position. Only in an emergency, such as a dead battery
or conserver malfunction, should the switch be set to
continuous flow. Be aware that continuous flow at 2 Lpm can empty
a full M6 cylinder in 1.4 hours. Should you find it necessary to
switch to continuous flow because you feel you are not getting enough
oxygen, you need to discuss your prescription and your settings with
your physician and your oxygen provider's respiratory therapist
- Batteries are required in some conservers to provide
electrical power. There is an indicator, usually a light, which changes
from green to amber to red as the battery weakens. Replace the battery
when the indicator turns amber. Do not wait until the indicator turns
red. Ask your oxygen provider to supply you with extra batteries.
Always carry a
backup set with you.
- Conservers have a rotary switch that is used to select the
size or frequency of a pulse. It may be a five-position switch with
markings 0, 1, 2, 3, and 4. It may be a seven-position switch with
markings 0, 1, 2, 3, 4, 5, and 6. It may be a twelve-position switch
with markings 0, .25, .5, .75, 1, 1.5, 2, 2.5, 3, 4, 5, and 6.
Manufacturers have demonstrated through research that these numbers are
"equivalent to" continuous flow rates with the same number. Keep the
switch in the 0 or off position, when not in use. Settings at 1 or
above provide a pulse. Settings less than 1 usually provide continuous
Conservers are designed
to provide a series of oxygen pulses that
your breathing. The design concept is simple—turn on the oxygen while
you inhale and turn it off when you exhale. Some conservers do just
that. They deliver a constant stream
of oxygen for about one second, beginning when an inhalation is
detected. Figure 2 shows the waveform of such a conserver at settings 2
and 4 (e.g., settings equivalent to continuous flow at 2 and 4
| Figure 2
Waveforms at 2 and 4 Lpm of a
|Source: Valley Inspired Products,
LLC at www.inspiredrc.com
conservers deliver oxygen for about 1 of
3 seconds, so they have a 2:1 savings ratio. Research studies support
the oxygen savings but most fail to support the efficacy of this type
As mentioned before, conservers are either electronic or
Electronic conservers may be either intermittent-breath or
every-breath conservers. The solenoid of an every-breath conserver
opens each time the sensor signals. The length of time it remains open
depends on the pulse volume setting, selected by the user. The higher
the pulse volume setting, the longer
the solenoid remains open. The solenoid of an intermittent-breath
conserver may skip one, two or three signals, depending on
the pulse frequency setting selected by the user.
Figure 3 shows the waveforms of two electronic conservers.
- At the left in Figure 3 you see the waveform of an
intermittent-breath conserver which has a fixed pulse volume and a
variable frequency. At setting 1, an intermittent-breath conserver
skips three breaths before delivering a pulse. The pulse at setting 2
occurs on every other breath whereas at setting 4, it occurs on every
breath. Typically, the volume of this pulse is between 35 and 40
- At the right in Figure 3 is the waveforms of an
every-breath conserver which has a fixed pulse frequency (every breath)
and a variable volume. Typically, the volume of this pulse is 15 to
17.5 ml at 1 Lpm and a multiple of this at higher settings.
Waveforms of Electronic Conservers
|Source: Valley Inspired
Products, LLC at www.inspiredrc.com
pneumatic conserver delivers oxygen
the user's inhalation. It delivers a pulse of about 1.2 ml at the
of an inhalation, followed by continuous flow until it senses the
beginning of exhalation. Figure 4 shows the 20 bpm user's waveform of
two pneumatic conservers.
Waveforms of Two Pneumatic Conservers*
|*20 bpm user
Source: Valley Inspired Products, LLC at
conservers typically use a dual lumen
cannula. This is necessary so that the end of an inhalation can be
detected and the oxygen flow cut off. The waveform you see in the
Figure 4 is of a 20 breaths per minute (bpm) user. The wave forms for
other breathing rates would be identical
except the tale of the metered flow would be correspondingly longer or
in the following table are the
discussed in this section, along with the amount of oxygen released
an inhalation, and the reported savings in oxygen as compared with
Output and Advertised
Over Continuous Flow
Your breathing rate
contributes significantly to the amount of oxygen
you receive from continuous flow or through one of the conservers shown
in the above table. One of the above conservers is said to last 7.78
hours for a 20 bpm user and
9.84 hours for an 18 bpm user. That means the slower breather gets 25
percent less oxygen.
conservers have a switch with four positions,
which permits the user to select how often a pulse occurs.
Conservers of this type include:
Therapeutics' OM 301, OM
302 "Sequoia" and OM 401
settings on these conservers do the following:
pulse volume is the same at all four settings. For the Sequoia and
Oxymatic 401, it is 40 ml. For the Oxymatic 301 and Impulse
models, it is 35
ml. (All but the Oxymatic 301 have a six-position
positions 5 and 6 on these conservers, pulses occur on every breath at
a slightly higher volume.).
- At setting 1, oxygen pulses during
one of four
- At setting 2, oxygen pulses on
- At setting 3, oxygen pulses during
three of every four inhalations.
- At setting 4 or higher, pulses occur
during every inhalation.
These conservers require a flashlight
and have a visual "low battery" indicator. Oxygen will stop flowing
when the battery is dead, when the conserver malfunctions, or when the
oxygen is depleted. In such emergencies, users of the Impulse
and Oxymatic 401 can switch to continuous flow at 2 Lpm.
A user of the Oxymatic
301 with a defective system or no new battery can change to
continuous flow only by disconnecting the conserver from the regulator
and cannula, and reconnecting the cannula directly to the regulator.
Users may find this changeover process stressful since it requires
several physically difficult
steps, all conducted with no oxygen. (See Q & A .)
|NOTE: Chad may have
discontinued sale of the Oxymatic 301,
Decker Medical, Inc. continues to market a look-alike as its React
Conserving Device (Model RCD 101). Airsep may have discontinued sale of
the Impulse Select. and is
marketing the Impulse Elite in
its place. Should your oxygen provider offer you either the Oxymatic 301 (or its look-alike) or
the Impulse Select, consider
negotiating for a more up-to-date conserver.
To avoid damaging the electrical
system, use caution
when removing the battery from the Oxymatic 301 . Be sure to
remove the battery so that it does not catch and stretch the coiled
battery spring. When stretched too far the spring will separate from
the circuitry at its base.
If the problems of the Oxymatic 301, described above,
are of concern to you, contact your oxygen provider and request an
Oxymatic 401 as a replacement. This donut-shaped unit can be easily
switched between pulse and continuous flow. Its new casing may also
have corrected the battery removal problem.
The Impulse Select
has audible warnings when no inhalation is detected. The Mode switch of
the Impulse Select is located in its battery compartment. To
change the mode, remove the
battery and, with a small slotted screw driver, move the white
switch in the center of the blue plastic housing to its left side for
Mode A or to its right side for Mode B. In Mode A the Impulse
Select is the intermittent-breath conserver, as described in this
section. In Mode B it is the every-breath conserver described in the
next section. (The Impulse Elite is an every-breath conserver
in both modes.)
conservers that provide a pulse of oxygen on every breath
Therapeutics' OM 411
The Oxymatic 411 is the
every-breath version of the
intermittent-breath Oxymatic 401 .
Elite (Modes A and B )
PulseDose, Models EX2000D and EX2005
Penox's Escort ( See the section "Liquid
Spirit (See the section "Liquid Oxygen.")
The Impulse Elite
(Modes A and B) user controls the volume
with a six-position switch that is preprogrammed to one of two modes.
In Mode A, the amount
of oxygen ranges from 8.75 to 52 ml and in Mode B between 16.5
and 99 ml. These modes are set with a toggle switch located in
the conserver's battery compartment.
- Both provide the equivalent of
between 10, 20, or 30
ml per breath, at settings 1, 2, or 3, respectively. For example, at
setting 2 the user of the Oxymatic 401 will receive a 40 ml
pulse on alternate inhalations while the Oxymatic 411 user
will receive a 20 ml pulse on every inhalation.
- Both deliver a pulse of 40, 50 or 60
ml on every
breath at settings 4, 5 or 6, respectively.
About the Impulse, Jim of Long Beach, CA
About a year ago my oxygen provider equipped me with
an AirSep Impulse conserver together with a supply of M6
cylinders. Once getting the proper setting, the Impulse
has performed flawlessly as it was designed. The unit itself is
convenient, flexible and easy to use. The carrying bag needed some
tinkering for accessibility and a new padded shoulder strap to make it
comfortable to wear over the shoulder. These are available in many
sporting goods stores.
The Impulse Select has two modes of operation. I
chose Mode A. You should work closely with your oxygen provider in
the right one for you. Insist that they explain to you how the unit
and how these modes are different. Care should be taken not to
accidentally move the slide switch on the side that sets the unit to
continuous flow. It moves much too easily. When the switch is in the
continuous flow position and the cylinder valve is open, your oxygen
cylinder will quickly empty.
The Wave 6200
is a rectangular conserver that attaches through
a tube to the regulator on an oxygen cylinder. Its manufacturer
recommends a cannula of length no more than 4 feet. To change to
continuous flow, the cannula must be removed from the conserver and
attached directly to the regulator.
Like both the Impulse and PulseDose
conservers, the Wave 6200 has audible and visual warnings that
indicate the battery needs replacing, the cylinder is empty, and
breathing is not detected. The PulseDose and Wave 6200
are the only conservers I have come across that have alarms reporting
an empty cylinder. These features may be particularly appealing to a
caregiver who needs help monitoring a patient.
The pulse of these conservers may not
be easily felt
or heard by the user, particularly at lower flow levels and in noisy
surroundings. The Impulse Select has audible alerts when no
inhalation is detected.
Each conserver permits the user to
flow when the battery is dead or the conserver malfunctions. On the
PulseDose a technician sets it to the user’s flow rate, up
to 6 Lpm. Continuous flow is factory preset at 2 Lpm on the other
conservers are every-breath conservers which operate on
oxygen pressure and require no batteries. All are donut-shaped and slide onto the cylinder
valve. Each has a contents gauge that displays the amount of oxygen
remaining in the cylinder.
Pneumatic conservers have a rotary selection knob with numerical
- At settings greater than 1, oxygen is delivered
as a pulse at each inhalation.
- At settings less than or equal to 1, oxygen may
be delivered in continuous flow.
Most pneumatic conservers have a continuous flow setting.
- When there is a continuous flow setting is on the rotary
selection knob, the flow rate is factory set at 2 Lpm.
- When there is a separate toggle switch to select between
pulse and continuous, the flow rate for continuous can be set with the
rotary selection knob.
Some pneumatic conservers automatically revert to continuous flow when
either inhalations are not detected or when the conserver fails.
Unlike electronic conservers, pneumatic conservers vent excess oxygen.
To minimize the accumulation of oxygen, you should use the approved
carrying bag and never carry the system under your coat.
Pneumatic Conservers with
The purpose of the second tube of the
cannula is to sense the end of an inhalation so that oxygen can be
provided during the entire inhalation period. One tube of this
cannula is attached to the conserver's sensing port and
the other to the oxygen port. There are two types of dual cannulas
available. One type commits one nostril to sensing and the other to
oxygen delivery. The other type allows nostrils to share these tasks.
If you use the former type and have a deviated septum or runny nose,
you may find the sensing
tube frequently becomes clogged. When this occurs, reverse the
of the tubes.
Of the conservers reported here, some require a cannula with
a single tube whereas others require a dual lumen cannula. The
operational difference is basically this--single lumen conservers
provide a pulse for a fixed duration, as electronic conservers do,
whereas those with dual lumen cannulas provide oxygen until the end of
an inhalation is detected.
Bennett's Helios 300
Helios (image) is discussed in the Liquid
section of this website.
Puritan Bennett's CR 50
CR-50 (image) is a 1.1 lb. pneumatic conserver that
requires a dual cannula. It attaches to a cylinder by slipping it over
the cylinder's neck and tightening it in place. The CR-50 comes
with carrying bag for
the cylinder and conserver that you are encouraged to use for two
reasons. First, it holds the cylinder in a vertical position, its best
operational position. Second, the bag is constructed to reduce the
oxygen. that vents from the conserver during its operation.
The CR-50 has a selection knob with numbered settings--0
(or Off), 0.25, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 4, 5, and 6. At settings
less than 1, the conserver delivers continuous flow.
At settings 1 or greater the conserver delivers a pulse at the
beginning of an inhalation, followed by continuous flow at the same
rate until exhalation is detected. For example, when set to 2, the
conserver delivers a 12 ml pulse followed by continuous flow at 2 Lpm.
By using a CR-50 , a 20 bpm, 2 Lpm user can make a cylinder
last about twice as long as the same cylinder set to continuous flow.
The CR-50 does not have a continuous flow setting. It defaults
to continuous flow when no inhalation is detected and when there
is any other conserver failure. The user can set the conserver to
continuous flow by momentarily covering the vent port, located
between the two cannula ports.
Victor Medical's O2N Demand II
The O2N Demand II (image) is a 1 lb. 6 oz. pneumatic conserver that
slips over the cylinder's neck and requires a dual cannula. It has a
toggle switch to set the flow to either pulse or continuous. It has a
rotary switch with eleven
user-selectable positions--0(or Off), 1, 1,5, 2, 2.5, 3, 3.5, 4, 4.5,
5, 5.5, and 6. The rotary switch controls the size of the pulse when
toggle switch is set to pulse and the continuous flow rate when
the toggle switch is set to continuous. When the toggle switch
is set to conserver and the rotary switch to 2, the 20 bpm user can
a pulse of about 46 ml.
The manufacturer offers a variety of carry bags, including those which
stand the cylinder vertical and those which permit the cylinder
to lie horizontal. With the toggle switch set to pulse.
the user can expect the attached cylinder to last twice as
long than when the toggle switch is set to continuous.
The O2Xpress is a 1 lb. every-breath pneumatic
conserver that requires a dual cannula. It has a built-in yoke that
fits over the neck of an oxygen cylinder. It comes with a carry
bag that positions the cylinder in a vertical position. It has a pulse
selection knob with settings 0 (or
Off), 0.50, 0.75, 1, 1.5, 2, 2.5, 3, 4, 5, and 6. At all settings
oxygen is delivered as a pulse during the first third of an inhalation.
This conserver has a savings ratio of 3:1.
Medica's OPA 830
830 is a 22 oz. pneumatic conserver that uses
a dual cannula. It is donut-shaped and slips over the cylinder's neck.
The carrying bags offered with this conserver allow the cylinder to
stand vertically or lie on its side. It has a contents gauge, a
continuous/pulse toggle switch, and a rotary selection knob with
numbered settings 1/2, 1, 2, 3, 4,and 5. When the toggle switch is set
to pulse, the selection knob controls the size of the pulse. At Setting
2 the pulse is 40 ml. When the toggle switch is set to continuous, the
selection know controls the rate of flow of continuous oxygen. At
Setting 2 the rate of flow is 2 Lpm. The OPA 830 has a savings
ratio of 2.5:1, meaning that when the toggle switch is set to pulse the
cylinder will last 2.5 times longer than when set to continuous.
Conservers with Single Cannulas
The Cypress (image)
pneumatic conserver which weighs 14.8 oz. and requires a single lumen
cannula.It's donut-shaped and slips over the cylinder's neck. It comes
with its own carrying bag. The bag encourages the user to keep the
Cypress in an upright position so it can function effectively. It
comes with a contents gauge and a pulse selection knob. When the
gauge's pointer is within the red area on the gauge, the
pressure within the cylinder is below 200 psi and the cylinder must be
The pulse selection knob has an Off, a CF (continuous flow), and 6
pulse settings positions.
- When set to CF, the Cypress delivers continuous flow
oxygen at a fixed rate of 2 Lpm.
- When set to a numbered position (1, 2, 3, 4, 5, or 6),
oxygen is delivered in a pulse at the beginning of each inhalation. At
setting 2, for example, the Cypress delivers a 32 ml pulse as
soon an inhalation is detected. At setting 1 the pulse is half that (16
ml) and at setting 4, twice that (64 ml). A user with a breathing
rate of 20 bpm can expect a cylinder to last three times longer than on
Medical's Easypulse (Model 8511
The Easypulse (image) is a 12.7 oz. pneumatic conserver
that requires a single lumen cannula. It comes with a carry bag that
orients the cylinder in a vertical position--the optimum operating
The Easypulse slips over the neck of an
oxygen cylinder. It has a needle gauge.which displays the amount of
oxygen remaining in the cylinder. When the needle is in the red
area, it is time to replace the cylinder with a full one.
Its flow control knob has seven
positions--Off, continuous flow, and five numbered positions (1, 2, 3,
4, and 5)..
- When set to continuous
flow, the conserver will deliver continuous flow at the factory set
rate of 2 Lpm. .
example, when set to 2, the conserver delivers 560 ml of oxygen per
minute.. At this setting, the 10 bpm patient receives ten
35 ml pulses and the 20 bpm patient receives twenty 28 ml. pulses.
The manufacturer claims that Easypulse will make a cylinder last
3 to 4.4 times longer than if the cylinder were on continuous flow at
the same rate. Thus, an M6 (B) cylinder, which empties in 1.4 hours on
continuous flow, should empty in 4.2 and 6.2 hours
the 2 Lpm user with a breathing rate of 20 bpm.
- When set to a numbered position,
the conserver will
deliver a fixed amount of oxygen during each minute.Patients with
slower breathing rates receive larger pulses than will patients with
faster breathing rates so, that after a minute, both receive about the
same amount of oxygen.
Is a "Pulse-Type"
Conserver For Me?
You may be among the many users of supplementary oxygen who use a
portable system that has a pulse-type conserver. This type of
conserver is used with both compressed and liquid portable systems.
This device delivers oxygen only when you inhale, thereby saving oxygen
for later use. Manufacturers claim that conservers can double or triple
an oxygen container's life when compared with continuous flow oxygen.
This means you can carry smaller oxygen containers or change (or fill)
your container less frequently.
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modified: July 20, 2012