Portable Oxygen: A User's Perspective
Conservers & Cannulas

A 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 cannula. 

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 basics.

How We Breathe

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 axis). 

As 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. 

Inside a Conserver

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 (RT).

• 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 oxygen flow.

How Conservers Work

Conservers are designed to provide a series of oxygen pulses that coincide with 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 Lpm). 

Such 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 of conserver. 

As mentioned before, conservers are either electronic or pneumatic. 

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 ml. 

• 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.

A pneumatic conserver delivers oxygen throughout the user's inhalation. It delivers a pulse of about 1.2 ml at the beginning 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. 

Pneumatic 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 shorter. 

Listed in the following table are the conservers discussed in this section, along with the amount of oxygen released during an inhalation, and the reported savings in oxygen as compared with 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.

Intermittent-breath conservers have a switch with four positions, which permits the user to select how often a pulse occurs. 

Conservers of this type include:

Chad Therapeutics' OM 301, OM 302 "Sequoia" and OM 401

The settings on these conservers do the following:

• At setting 1, oxygen pulses during one of four inhalations. 
• At setting 2, oxygen pulses on alternate inhalations. 
• At setting 3, oxygen pulses during three of every four inhalations. 
• At setting 4 or higher, pulses occur during every inhalation. 

The 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 switch. At positions 5 and 6 on these conservers, pulses occur on every breath at a slightly higher volume.).

These conservers require a flashlight type battery 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, but Cramer 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.)

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Every-Breath Conservers

Electronic conservers that provide a pulse of oxygen on every breath include: 

Chad Therapeutics' OM 411
Airsep's Impulse Elite (Modes A and B ) 
Devilbiss' PulseDose, Models EX2000D and EX2005 
CPI's Wave 6200
Penox's Escort ( See the section "Liquid Oxygen.")
Caire's Spirit (See the section "Liquid Oxygen.") 

The Oxymatic 411 is the every-breath version of the intermittent-breath Oxymatic 401 .

• Both casings look alike. 

• 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. 

 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.

About the Impulse, Jim of Long Beach, CA writes: 

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 choosing the right one for you. Insist that they explain to you how the unit operates 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 select continuous 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.

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Pneumatic Conservers

Pneumatic 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 settings.

• 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 Dual Cannulas

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 ports of the tubes.

Puritan Bennett's Helios 300
Helios (image) is discussed in the  Liquid section of this website.

Puritan Bennett's CR 50
The 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 accumulation of 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 the 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 expect 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.

Salter Lab's O₂Xpress (Model 8511)
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.

Western Medica's OPA 830
The OPA 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.

Pneumatic Conservers with Single Cannulas

Chad's  OM-511 Cypress
The Cypress  (image) is a 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 replaced.

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 continuous flow.

Precision 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 position

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 labeled 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. .

• 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.  

For 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 for the 2 Lpm user with a breathing rate of 20 bpm.

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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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Last modified: July 20, 2012