Guide to Prescribing Conserving Device Technology

Guide to Prescribing Home Oxygen

by Thomas
L. Petty, M.D.


Key to Prescibing Home Oxygen


to Successful Treatment

Oxygen Options

Conserving Device

and Reimbursement

Considerations in Selecting Equipment

Thomas L. Petty, M. D.

Conserving Device Technology

Conserving Devices; Demand vs. Pulse

Oxygen conserving devices can substantially increase the range of a
liquid portable or small high- pressure gas system. Some devices are
mechanical/pneumatic and others are battery powered. The initiation of
inspiration causes a pulse flow of oxygen to be delivered. Not all
conserving devices deliver the same amount of oxygen. Checking for
adequacy of oxygenation by the use of pulse oximetry, particularly during
exercise, should be done when conserving devices are used. The
classification of conservers is often misleading. Some conservers are
referred to as demand devices because they are triggered by patient demand
even though they only deliver a fixed pulse. In reality, there are two
general classifications of oxygen conservers. Those that deliver a fixed
volume per breath are classified as pulsing devices. Those that deliver a
variable volume (commensurate with the length of inspiration) are demand
devices. Other demand devices deliver for a fixed time that is
approximately the length of inhalation.

Pulse Devices

Some pulse devices deliver every breath, others on alternate breaths.
The alternate breath devices deliver a fixed volume (36 ml) 3 out of 4
breaths at a setting of 3, 2 out of 4 at a setting of 2 and 1 out of 4 at
a setting of 1 and activate with each breath on a setting of 4. Other
devices in this category deliver a fixed volume of up to 16 ml times the
setting number (1 through 4) each time the conserver is triggered.

All pulse type devices share some common characteristics:

  • They deliver fixed volumes for each flow setting each time a pulse
    is triggered.
  • They do not deliver any more or less volume as the length of the
    patient’s inspiration time varies.
  • They tend to deliver less than prescribed of oxygen per minute
    volume at low breath rates but can deliver more at high breath rates,
    e.g., during exercise.
  • They tend to require more patient attention to conserver function to
    permit manually switching from conserver mode to continuous flow in case
    of conserver malfunction.

The settings used on the flow control may or may not provide the same
delivered minute volume during inspiration as that provided by continuous
flow. This is particularly true of pulse type devices.

Control device on top of oxygen containerDemand

By comparison, demand devices will vary the amount of oxygen delivered
on each and every breath consistent with the length of time the patient
inhales. Demand type devices such as the Puritan-Bennett C550 and CR50
deliver a 12ml bolus followed by continuous flow throughout the remainder
of inspiration. No oxygen is delivered during exhalation.

Demand devices also exhibit other shared characteristics:

  • Following the initial bolus they deliver at the equivalent flow rate
    of continuous flow for the remainder of the inspiration.
  • They deliver a variable volume at each flow setting depending on the
    length of inspiration.
  • They have lower levels of savings at low breath rates but at a given
    setting can save as much as or more than pulse devices at high breath
    rates and high I.E. ratios.
  • They tend to deliver volumes equal to or greater than those received
    with continuous flow therapy for most settings.
  • They generally revert automatically to continuous flow without
    patient interaction in the event of conserver malfunction.