Electronic Demand Pulsed-Dose oxygen delivery systems deliver oxygen to the patient by detecting the patient's inspiratory effort and providing gas flow during the initial portion of inspiration. This method reduces the amount of oxygen needed by 50 to 85% (compared to continuous flow) and significantly reduces the cost, the supplies needed, and the limitations on mobility caused by a limited oxygen supply.
As the patient initiates a breath, the cannula tip senses the flow, a solenoid valve opens, and a burst of oxygen is rapidly delivered to the patient. The size of the burst or flow varies among different manufacturers. The pulsed-dose system takes the place of a flowmeter during oxygen therapy and is attached to a 50 psig gas source. In most devices the operator can select the gas flow and the mode of operation (either pulse or continuous flow). A battery-powered fluidic valve is attached to a gaseous or liquid oxygen supply to operate the system.
Other methods used to further reduce oxygen usage when using the pulse-demand system is to reduce the dose of oxygen delivered to the patient during each pulsation and/or to deliver a burst only on the second or third breath instead of every breath. In addition, the size of the oxygen pulse dose will change with the flow setting with increases in flow delivering larger doses of oxygen and vice versa. All of the above variations will differ among the various manufacturers.
Potential problems encountered when using the pulse-demand system will include either no oxygen flow from the device or decreased oxygen saturations in the patient. If no oxygen flow is detected, then possible causes may include a depletion of the gas supply, an obstruction or disconnection of the connecting tubing, or an inability of the device to detect the patient's effort to breath. If the device cannot detect the patient's inspiratory effort, the sensitivity will need to be increased or the nasal cannula will need to be repositioned in the nares.
A decrease in the patient's oxgyen saturation should always be a cause for alarm and may indicate a change in the patient's medical status, tachypnea, or a failure in the device. In any case, a backup system should be available in order to verify whether the problem is with the device or with the patient.
Limitations of the Pulsed-Dose System:
- The high cost of the system.
- Technical problems may be associated with such a complicated device. This may include disconnections, improper placement of the device, and a possible device failure.
- The lack of accomodation for an increased need during exercise, stress, illness, ect.
- The operation of the device can vary if not properly setup.
- The size of the burst or flow varies among different manufacturers and should be taken into consideration when purchasing.