Portable oxygen concentrators (POCs) have made supplemental oxygen therapy more manageable. These devices use a pulse dose delivery system, providing oxygen in short bursts, or a “bolus,” only when the user begins to inhale, unlike continuous flow. This demand-flow mechanism conserves oxygen, allowing the unit to be smaller and the battery to last longer. Correctly setting the pulse dose is paramount to ensure adequate blood oxygen saturation ($S\text{pO}_2$) is maintained during rest and activity. Because pulse dose settings are not standardized, a setting on one manufacturer’s machine will not deliver the same volume of oxygen as the same setting on another brand’s machine.
Translating the Oxygen Prescription
The primary challenge in setting a pulse dose machine is that prescriptions are frequently written in terms of continuous flow, typically measured in liters per minute (L/min). This constant flow rate, such as 2 L/min, is structurally different from the intermittent delivery of a pulse dose device. Pulse dose settings are usually represented by a number and are calibrated by the manufacturer in milliliters (mL) per breath or in milliliters per minute (mL/min).
Since there is no direct, universal conversion from L/min to a pulse dose setting number, patients must consult their equipment provider or the device’s technical specifications. Manufacturers often provide a chart to approximate the continuous flow requirement to a pulse setting based on a standardized breathing rate. This theoretical conversion provides the starting point for titration, but the actual oxygen volume received depends on the device’s specific bolus size and the user’s breathing pattern, which changes throughout the day.
Titrating the Baseline Setting at Rest
The process of determining the correct resting setting is called titration and requires the use of a pulse oximeter, which measures the percentage of oxygen saturation in the blood ($S\text{pO}_2$). The goal is to find the lowest pulse dose setting that maintains the target $S\text{pO}_2$ level specified by the prescribing physician. For most patients, this target is typically 94–98%, though saturation above 90% is generally considered safe. Patients with chronic obstructive pulmonary disease (COPD) may have a lower target range, often 88–92%, to avoid complications.
The titration process should begin by sitting quietly at rest for at least five minutes to establish a stable baseline $S\text{pO}_2$ reading without supplemental oxygen. Once the baseline is noted, the portable concentrator should be turned on and set to the initial pulse setting determined from the conversion chart. Wait 10 minutes after starting the oxygen or changing the setting before taking a new $S\text{pO}_2$ reading, allowing the body’s oxygen levels to stabilize.
If the measured saturation is below the physician’s target, the pulse dose setting should be increased by one level, and the patient should wait another 10 minutes before rechecking. Conversely, if the saturation is consistently above the target, the setting can be decreased to find the minimum effective dose. This methodical adjustment ensures the patient receives adequate oxygen without over-oxygenation. The resulting setting that maintains the target $S\text{pO}_2$ is established as the baseline resting setting.
Adjusting Pulse Settings for Activity
The baseline setting determined during rest is rarely sufficient for periods of physical exertion because activity increases the body’s metabolic demand and respiratory rate. When a person moves, they breathe faster and often shallower, which can cause the $S\text{pO}_2$ to drop quickly below the target threshold. Therefore, the pulse dose setting must be tested and adjusted while performing common daily activities.
To find the correct setting for activity, the user should wear the pulse oximeter and perform a task such as walking a certain distance or climbing a flight of stairs. If the $S\text{pO}_2$ drops below the lower limit of the target range, the activity should be paused immediately. The pulse dose setting must then be increased by one level, and the activity resumed to see if the new setting maintains the target saturation.
This process should be repeated for different levels of activity until the lowest effective pulse setting is identified for each specific task. Patients should keep a record of these personalized settings, noting, for example, that “Walking the dog requires Setting 4” or “Light housework requires Setting 3.” This documentation ensures consistent and appropriate oxygen delivery during all waking hours. If the device is used overnight, the setting may need separate titration for sleep or the device may need to be placed in a specific sleep mode.
Monitoring and Troubleshooting
The accuracy of pulse dose delivery relies heavily on the concentrator’s ability to sense the beginning of an inhalation, known as the triggering mechanism. If the device fails to detect a breath, it will not deliver the oxygen bolus, leading to inadequate saturation. Shallow breathing, mouth breathing, or a poorly positioned nasal cannula can interfere with this mechanism.
Regular maintenance is necessary for consistent performance. This includes checking the cannula for kinks or twists and ensuring the tubing is securely connected. The device’s air intake vents must remain unobstructed to prevent overheating and maintain oxygen purity. Any change in the sound of the device or the appearance of a warning light should prompt a check of the user manual for troubleshooting steps.
If the patient follows the titration protocol and finds they cannot maintain the prescribed $S\text{pO}_2$ even at the highest pulse dose setting, they must immediately contact their physician or equipment provider. This indicates the portable concentrator may not be capable of delivering the required volume of oxygen, or the patient’s respiratory needs have changed significantly. In such cases, the patient should switch to a backup oxygen source as directed by their care team.