An oxygen conserving device (OCD) is a specialized regulator accessory used with supplemental oxygen systems, primarily portable compressed gas cylinders or liquid oxygen units. Its function is to deliver oxygen to the user more efficiently than a standard continuous flow regulator by reducing the amount of wasted gas. This efficiency is achieved by delivering oxygen only when the user is actively inhaling, instead of supplying a constant stream of gas. By minimizing the oxygen lost during the exhalation phase, the device significantly extends the duration of the portable oxygen supply.
The Science of Pulsed Delivery
The fundamental science behind oxygen conservation is known as demand flow or pulsed dose delivery. This method is a direct response to the physiological reality that the body can only effectively absorb oxygen during the initial phase of inhalation. Oxygen supplied through a traditional continuous flow system is simply released into the air and wasted during exhalation or the pause between breaths.
A conserving device uses a highly sensitive electronic or pneumatic sensor to detect the precise moment a patient begins to inhale. The start of inhalation causes a slight pressure swing or vacuum within the nasal cannula tubing, which the device immediately registers. Upon detection, a valve instantly opens to release a precisely measured burst, or bolus, of oxygen into the nasal passages. This bolus is delivered within the first approximately 250 milliseconds of the inspiratory cycle, ensuring the concentrated oxygen reaches the lungs when gas exchange is most productive.
The volume of this oxygen bolus is typically measured in milliliters per breath, rather than the liters per minute used in continuous flow settings. The device then closes the valve for the remainder of the breath cycle, preventing oxygen from being wasted. This synchronization means that a setting on the conserver, such as “2,” corresponds to a specific volume of oxygen delivered per breath, not a continuous flow rate. This pulsed delivery can reduce oxygen usage by 50% or more compared to continuous flow.
Categorizing Oxygen Conserving Devices
Oxygen conserving devices can be broadly categorized based on their mechanism of action, which determines how they sense the breath and control the valve. The most common categories are electronic and pneumatic conservers, representing the spectrum from high-tech precision to mechanical simplicity. Electronic conservers are battery-powered and use sophisticated sensors and logic circuitry to detect the subtle pressure changes associated with inhalation. These devices offer high precision in controlling the bolus size and often include features like alarms for low battery or failure to detect a breath.
Pneumatic conservers are simpler and use the pressure changes of the breathing cycle itself to mechanically trigger the oxygen release valve. They do not require batteries, making them lighter and requiring less maintenance than their electronic counterparts. However, pneumatic devices may be less sensitive and can sometimes delay the oxygen pulse, which could reduce the efficiency of oxygen uptake in some users.
Beyond these active, demand-flow devices, a simpler, passive form of conservation is offered by reservoir cannulas, such as the pendant or mustache style. These systems incorporate a small pouch or reservoir into the tubing that collects a small volume of oxygen during the exhalation phase. When the user inhales, they pull in a mixture of room air and the concentrated oxygen that has been stored in the reservoir. Although less efficient than electronic demand-flow systems, these reservoir cannulas can still provide a conservation ratio ranging from 2:1 to 4:1 by enabling a reduction in the required oxygen flow setting.
Enhanced Mobility and Supply Longevity
The primary practical benefit of using an oxygen conserving device is the substantial increase in the duration of a portable oxygen supply. By eliminating wasted gas, these devices allow a patient to use a smaller, lighter oxygen cylinder for the same duration, or use a standard tank for a significantly longer period. This conservation efficiency, often described as a ratio of 3:1 up to 7:1 compared to continuous flow, translates directly into supply longevity.
This extended duration directly enhances patient mobility and independence, addressing the challenges of using supplemental oxygen outside the home. Patients can participate in extended activities, travel, or run errands without the constant worry of an oxygen tank running empty. The ability to use smaller, lighter cylinders reduces the physical burden on the user. Furthermore, conserving gas reduces the frequency of necessary tank deliveries or refills, which can result in economic savings.