Understanding the Dial on Large Volume Nebulizer Bottles

Large volume nebulizers are a cornerstone of respiratory therapy, designed to provide humidity to the airway over extended periods. This is especially important when using oxygen, as it is an anhydrous gas that lacks moisture and can dry out the airways. However, confusion often arises regarding the role of the dial on the nebulizer bottle, particularly when working with different air and oxygen sources.

In this post, we’ll outline three common scenarios where large volume nebulizers are used and clarify how the dial functions—or doesn’t—in each situation.

Scenario 1: Using an Oxygen Pipeline (High-Pressure)

In many clinical settings, oxygen pipelines serve as a high-pressure source, delivering oxygen directly to the nebulizer.

• How it works: The pipeline provides both the pressure and the oxygen content required for the nebulizer to generate cool humidity effectively.
• Role of the dial: The dial adjusts the FiO2 concentration delivered to the patient by mixing the high-pressure oxygen from the pipeline with room air through a Venturi effect. Manufacturers often specify flow meter settings (e.g., 5, 8, or 10 LPM) needed to achieve various FiO2 levels. After setting the flow meter, you turn the nebulizer dial to the desired FiO2. For example, if the flow meter is set to 8 LPM and the dial is set to 40%, the nebulizer will mix oxygen and room air to approximate 40% FiO2, even though 8 LPM alone would normally generate 52% FiO2.
• Best for: High-accuracy oxygen delivery with consistent humidification over extended periods.
• Key Takeaway: The dial plays a critical role in regulating FiO2 when using an oxygen pipeline (wall oxygen), as both the pressure and oxygen are integrated into the source.

Scenario 2: Using a 50PSI Compressor (with Oxygen Bleed-In)

A 50PSI compressor delivers high-pressure air without oxygen. In these cases, oxygen must be bled into the system separately to achieve the desired FiO2. This is the most common method we see in skilled nursing facilities and at home.

• How it works: The compressor provides the necessary pressure to create cool humidity, while oxygen is introduced through a bleed-in port.
• Role of the dial: In this scenario, the dial does not regulate FiO2. Instead, it controls the amount of humidity delivered to the patient, as the oxygen concentration depends entirely on the bleed-in rate. The lower the FiO2 you set on the dial, the less humidity the patient receives. We typically recommend setting the dial between 40% and 60% to balance effective humidity delivery with patient comfort. However, keep in mind that there is not a significant difference in the amount of humidity delivered when the large volume nebulizer bottle’s FiO2 dial is set anywhere between 28% and 100%.
• Best for: Settings where oxygen from a wall source is unavailable, but compressed air is accessible, and oxygen concentration needs to be customized. Note that most concentrators alone do not produce sufficient pressure to be connected directly to the nebulizer bottle (more on that later).
• Key Takeaway: When using a compressor, the dial is primarily a humidity regulator (albeit with minimal variation across settings), while FiO2 is controlled by the oxygen bleed-in rate. Additionally, there are two common locations for connecting the bleed-in valve:

The further the bleed-in valve is from the patient, the more the oxygen may be diluted before reaching them.

Scenario 3: Using a "High-Intensity" Oxygen Concentrator

Some oxygen concentrators market themselves as high-pressure sources, delivering both pressure and oxygen directly to the nebulizer. However, the reliability of these devices for consistent performance can be questionable.

• How it works: The concentrator provides both oxygen and pressure, theoretically eliminating the need for a 50PSI compressor. However, its ability to maintain the high pressure required to produce cool humidity is inconsistent. This inconsistency can result in inadequate humidity or fluctuating FiO2 delivery to the patient.
• Role of the dial: Theoretically, the dial adjusts the FiO2 concentration in the same way it does with a pipeline source, mixing oxygen with room air via a venturi effect. However, if the concentrator’s pressure output or oxygen purity fluctuates, the dial’s accuracy becomes unreliable.
• Best for: Low-demand settings or as a backup option when other high-pressure sources, like oxygen pipelines or compressors, are unavailable.
• Key Takeaway: Exercise caution with oxygen concentrators claiming high-pressure (50PSI) output. Use a FiO2 analyzer to verify the concentrator’s actual performance. The dial’s functionality—and the overall effectiveness of the nebulizer—depends heavily on the concentrator’s ability to maintain consistent pressure and oxygen purity.

When Does the Dial Matter?

The dial on a large volume nebulizer only comes into play when the device is connected to a 50PSI source that already contains oxygen—such as an oxygen pipeline (wall oxygen) or certain oxygen concentrators. When oxygen must be bled into the system, the dial’s primary function is to regulate the amount of humidity delivered to the patient, not the FiO2.

Final Thoughts: Matching the Source to the Scenario

Understanding the relationship between the oxygen source, the dial, and the desired outcome is critical for effective nebulizer use. Here’s a quick summary:

• Pipeline (50PSI Oxygen): Dial controls FiO2.
• Compressor (50PSI Air): The dial regulates humidity and airflow, while FiO2 is determined by the oxygen bleed-in rate.
• Concentrator (50PSI Oxygen): Dial theoretically controls FiO2, but reliability depends on the device’s performance.

By understanding these distinctions, you can ensure your patients receive both proper humidification and the oxygen they need to meet their clinical requirements.