Medical gas flowmeter overview vector illustration

Medical Gas Flowmeters: An Overview (2024)

by | Updated: Mar 14, 2024

Flowmeters play a crucial role in healthcare settings, ensuring the precise delivery of medical gases to patients.

These devices are essential for maintaining patient safety and ensuring the effectiveness of medical procedures.

From oxygen to medical air, the accurate control of gas flow rates is paramount in healthcare facilities.

In this article, we will delve into the importance of medical gas flowmeters, their various types, and their indispensable role in modern medicine.

What is a Flowmeter?

A flowmeter is an essential device used in oxygen therapy to regulate and measure the flow rate of oxygen that is delivered to a patient. It is a crucial component of oxygen delivery systems, which can include oxygen cylinders, concentrators, and hospital piping systems.

Oxygen Flowmeter Thorpe Tube Vector
The primary objective is to ensure the precise amount of oxygen is administered to meet the patient’s therapeutic needs, thereby optimizing the effectiveness of the treatment while minimizing potential complications.

Flowmeters come in various designs, but they all have the same fundamental function: regulating oxygen flow in a range that usually varies between 0 to 15 liters per minute (LPM).

The settings can be adjusted according to the patient’s specific medical condition, age, and treatment plan, as prescribed by a healthcare professional.


A typical flowmeter consists of a control valve and a calibrated scale.

The control valve is used to adjust the flow rate, and the scale provides a visual indication of the flow rate in LPM.


Flowmeters are used in various clinical settings, including hospitals, clinics, and home care environments.

They are indispensable in treating conditions that affect oxygenation, such as chronic obstructive pulmonary disease (COPD), asthma, pneumonia, and during surgical procedures requiring anesthesia.

Incorrect flow rates can lead to hypoxemia, which can be life-threatening; therefore, the importance of a reliable and accurate flowmeter cannot be overstated.

Types of Flowmeters

Flowmeters come in various forms, each suited to specific applications and requirements.

The three primary types of flowmeters used in medical settings include:

  1. Flow restrictor
  2. Bourdon gauge
  3. Thorpe tube

Flow Restrictor

Flow restrictors are the simplest form of flowmeters designed for low-cost and low-maintenance situations.

They operate on a fixed orifice calibrated to allow a specific flow rate of gas through, which is determined by the pressure differential across the restrictor.

While they don’t offer the adjustability of other flowmeters, flow restrictors are reliable and ideal for use in systems where a constant flow rate is sufficient.

Bourdon Gauge

The Bourdon gauge is a flowmeter that measures the pressure of gas within a curved tube, which straightens as pressure increases.

The movement of the tube’s end is translated into a dial reading that indicates the flow rate.

This type of gauge is particularly robust and can measure higher pressures accurately, making it suitable for use with gases that require such conditions.

Thorpe Tube

The Thorpe tube, a staple in many medical environments, is known for its precision and adjustability.

It consists of a vertically mounted, tapered tube with a float inside that rises or falls with the gas flow rate, providing a direct reading of the flow.

This type can be connected to a central gas supply system and is often used for delivering oxygen therapy, as it allows healthcare professionals to adjust the flow rate according to the patient’s needs.

Note: The selection of a flowmeter type depends on various factors, including the required precision, the nature of the medical gas being used, the necessary flow rate range, and the specific healthcare application.

Selecting the Appropriate Type of Flowmeter

A flow restrictor is commonly utilized for supplying a fixed flow of air or oxygen to a medication nebulizer.

When combined with an oxygen E cylinder, an adjustable flow restrictor can tailor the flow to various devices, including oxygen delivery systems, medication nebulizers, or resuscitation bags.

It’s critical to note that any constriction or kinking in the oxygen tubing leading to these devices can impede the flow of gas.

The Bourdon gauge is preferable in situations where a flowmeter cannot be kept vertical, such as when transporting a patient with an oxygen E cylinder.

It’s essential to be aware that any narrowing or kinking in the oxygen tubing may decrease the flow of gas, even though the flow reading on the Bourdon gauge may not indicate this change.

For precise gas flow measurements, especially with devices that have high resistance, a compensated Thorpe tube is recommended over a Bourdon gauge.

Therefore, flow meters that can quickly connect are typically installed on most oxygen and air outlets in areas where patients are treated.

FAQs About Flowmeters

What is a High-Pressure Reducing Valve?

A high-pressure reducing valve is a device designed to lower the pressure of gases from high-pressure cylinders to levels that can be safely used in medical applications.

This valve is critical for ensuring that the gas flow is delivered at a consistent and manageable pressure, suitable for direct therapeutic use or for further regulation by medical gas flowmeters.

What is the Best Type of Flowmeter?

The “best” type of flowmeter depends on the specific medical context and needs.

For precise control and measurement of gas flow, especially in critical care or respiratory therapy, the Thorpe tube is widely regarded for its accuracy.

However, for robustness and mobility, the Bourdon gauge is often preferred.

Ultimately, the best flowmeter is one that aligns with the required medical standards, the type of gas being used, and the specific needs of patient care.

What is a Green Flowmeter Used For?

A green flowmeter is typically associated with the delivery of oxygen.

The color-coding is standardized to help prevent medical errors by ensuring that healthcare providers can quickly identify the correct gas type.

Green flowmeters, therefore, are used to control and monitor the flow of oxygen to patients in a variety of medical settings.

What is a Yellow Flowmeter Used For?

A yellow flowmeter is generally used for delivering medical air.

Medical air, which is filtered and free from moisture, is used in a variety of treatments such as nebulized drug therapy.

Similar to the green flowmeter for oxygen, the yellow color-coding helps distinguish it easily to prevent the incorrect administration of gases to patients.

What is a Medical Gas Cylinder?

A medical gas cylinder is a specially designed container used to store and transport gases for medical use, such as oxygen, nitrous oxide, and medical air, under high pressure.

These cylinders are made of materials that can safely contain the pressurized gas and are equipped with valves to control the release of gas as needed.

They are essential in healthcare settings for various applications, including anesthesia, respiratory care, and emergency medical services.

Final Thoughts

A flowmeter is a key device in oxygen therapy used for precisely regulating and measuring oxygen delivery to patients.

Its role is critical in ensuring that the therapy is both effective and safe, tailored to individual patient needs.

As technology continues to advance, newer types of flowmeters are expected to provide even more accurate and reliable measurements, further enhancing the quality of medical gas therapy.

John Landry, BS, RRT

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Davidson J, Gazzeta C, Torres LC, Jardim JR, Nascimento OA. Precision and accuracy of oxygen flow meters used at hospital settings. Respir Care. 2012.
  • Gurudatt C. The basic anaesthesia machine. Indian J Anaesth. 2013.

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