Overview of oxygen connector types

The tapered, barbed connector is a commonly encountered component for connecting oxygen delivery devices to flowmeters (e.g. flowmeter on a portable oxygen concentrator, cylinder or wall connected flow meter). This connectors is sometimes referred to as a ‘Christmas (fir) tree connector’ because of its shape and sometimes green color.

This connector comes in plastic or metal and simply screws on by hand (and can be damaged by over tightening).

Low pressure smooth bore oxygen tubing is connector to the barbed end of this adapter, as discussed in the next section.

CAUTION: this connection is not secured and accidental disconnect is common (especially if not applied with adequate force or if pressure is high)

Smooth bore oxygen tubing is an essential piece of oxygen delivery equipment. It is designed to be used with low pressure oxygen sources. This tubing comes in different colors (green or clear) and lengths and is often integrated into the delivery devices (e.g. nasal cannula or facemask). To connect smooth bore oxygen tubing to the oxygen source, the end of the tubing with a tapered opening is simply pushed over the tapered, barbed connector of the source by hand.

Two-sided, tapered, barbed plastic adapters may be obtained to connect smooth bore oxygen tubing extensions when needed.

Oxygen tubing must adhere to many specifications to ensure safety – these include transparency, strength, anti-kink design and other features.

(Use the slider at the top left of this page to see more advanced information on oxygen tubing)

A number of devices and techniques are used for splitting one oxygen source to multiple delivery devices. Not all are recommended and some can be dangerous for both patients and providers. Always consult the manufacturer’s specifications.

Oxygen connectors are often improvised in resource-constrained settings (see image below), but this practice can be very dangerous.

Devices that are often used for splitting include:

• Flowmeter stands (aka flowmeter stations or assemblies) – these boxes allow input from one oxygen source and then split that source into multiple outlets, each controlled by an independent flowmeter. These can be costly and require clear labeling of flowmeter-bed to avoid inadvertent titration for the wrong patient. These can be connected to an oxygen concentrator, though max total flow will be limited by the output of the oxygen concentrator.
• Dual flowmeters – as the name implies, this is a flowmeter with input from one oxygen source but output to two flowmeters. These require a high pressure oxygen source.
• Plastic flow splitter – this may be as simple as a y-connector. Setups using plastic flow splitters may result in unequal distribution of oxygen to patients due to limited ability to measure and control flow

There are multiple types of humidification systems and many can be placed in a low pressure oxygen delivery setup. The most common is the non-heated bubble humidifier. These simple devices come as either single use or reusable units and connect directly to a flowmeter. These devices require sterile or distilled water and are generally not efficient as compared to heated humidification systems (for full discussion, see Respiratory care humidifications systems)

Bubble humidifiers reduce the dryness of the oxygen supplied by bubbling the gas through water at room temperature. They must be filled with clean water at least once a day (distilled water, sterile or tap water that has been boiled and cooled) and the water level should be checked twice daily.  The humidifier equipment must be washed and disinfected regularly to prevent bacterial colonization.

Humidification is likely indicated with higher O2 flow rates through nasal prongs (>1 L/min for a neonate, >2 L/min for an infant, >4 L/min for an older child or adult) or with devices that bypass the humidifying nasal passages (e.g. nasopharyngeal catheter).

There is not standard definition for intermediate pressure oxygen. Here we define ‘intermediate pressure’ as oxygen pressure at ~3.45 bar (50 psi).  Many oxygen delivery devices require this pressure for safe function. In other words they will not function with unregulated, high pressure directly from a cylinder, and would also not work with low pressure from a portable oxygen concentrator. Of note, some ventilators, CPAP/BIPAP/NIPPV machines, and high flow nasal cannula have built in turbines or compressors that may allow them to function without an intermediate pressure oxygen source.

There are more than a dozen ‘standards’ for high pressure oxygen hose or wall fitting around the world. Unfortunately, many countries and regions have created their own standards which are not cross compatible. In some regions, especially in low and middle-income countries, it is common to encounter multiple different types of connectors. In Canada and the US, new construction uses the CGA DISS connector, though multiple ‘quick connect’ styles are commonly found. These quick connect devices may provide convenience but at a potential cost for durability and reliability.

Here we summarize the most common 18 high pressure hose and piped terminal oxygen connector – DISS, NIST, Puritan Bennett, Japanese Style, British Standard, German DIN, AGA Swedish, Italian UNIFOR, Ohmeda quick connect, DISS, Chemetron, Oxyequip, French AFNOR, Australian SIS, Schrader and more.

Connecting to an intermediate pressure (3.45 bar/50 psi) source requires specializes oxygen tubing to ensure safety. The smooth bore oxygen tubing described above is not sufficient – the tubing is not able to maintain integrity and would not remain securely connected to the source during intermediate pressure.

Rubber tubing that is reinforced (often braided polyester yarn coated in rubber) and intended for medical use is required. Color coding of such tubing and end connectors will vary by region. The working pressure of the hose may vary by the gas it was intended to be used with – ie make sure you are using the correct type of gas hose. Always check with local manufacturer’s and standards.

High pressure (in the context of clinical oxygen delivery systems) is most commonly defined as oxygen pressure at 100-200 bar (>2000 psi) or higher.  This pressure is unsafe to deliver to patients and must by regulated to a lower pressure before connecting to medical equipment or oxygen delivery devices.

Cylinder regulators serve to modulate pressure from a high pressure (100-200 bar) oxygen source to provide a reduced and stabilized intermediate outlet pressure (usually 3-6 bar). Importantly, properly functioning regulators enable the outlet pressure/flow to remain near constant regardless of fluctuations in pressure of the oxygen cylinder. Regulators which provide a stabilized flow output (otherwise known as flow gauges) have a flowmeter integrated into the same mechanical fitting. It is also possible to connect a flowmeter to the outlet port of a regulator stabilizing pressure to supply oxygen directly to patients (see image below).

Regulators which provide a stabilized pressure are used in conjunction with equipment (i.e., anesthesia machines, ventilators, high flow nasal oxygen delivery devices, etc.), while regulators which provide a stabilized outlet flow can be used to supply oxygen directly to patients.

There are multiple types of regulators, including:

• Single gauge regulator – has a set pressure output and displays pressure of the source content. Can be connected directly to a patient via a flowmeter
• Dual gauge regulator – with one gauge (‘inlet gauge’) showing the pressure of the source content and the second gauge showing the reduced outlet pressure which can be controlled with a knob or screw.

It is important to ensure a regulator outlet pressure is in the desired range and fits the cylinder (i.e. gas type).

Bourdon gauges measure the pressure of a gas contained in a compartment (e.g. cylinder). They are the most commonly used pressure gauges in medical gas equipment. Of note, Bourdon gauges display ‘gauge pressure’ which is not the same as ‘absolute pressure’ which includes atmospheric pressure, so Bourdon gauges function similarly at any altitude.

Dial (click) meters are calibrated to deliver a set flow at a constant pressure (3.45 bar, 50 psig). The flow is selected via an adjustable dial which displays the flow in a small window. Dial (click) meters come in various ranges of flow depending on the patient care need. Importantly, dial (click) meters are only accurate at their rated pressure.

This type of valve has an integrated pressure regulator and flowmeter and are found more commonly on smaller cylinders.

Pin index/yoke valves utilize the Pin Index Safety System (PISS) which is designed to ensure the correct connection via a unique pin arrangement by gas type. For example, pin index/yoke valves for cylinders containing oxygen have the specific pin arrangement displayed above (*click on Pin index/Yoke valve image to display).

In the US and Canada, CGA 580 is considered standard for industrial use while CGA 540 and 810 are considered standard for medical use.

Handwheel valves

Leaks in oxygen infrastructure and delivery devices are common. Common causes to include:

• User error – e.g. using excess flow
• Not turning off devices that are not in use (e.g. anesthesia machines or flowmeters)
• Incorrectly secured fitting from cylinders
• Leaks in high or low pressure tubing due to lack of adequate maintenance

There are many ways to conserve oxygen, including through regular inspection and routine maintenance.

1. WHO-UNICEF technical specifications and guidance for oxygen therapy devices. Geneva: World Health Organization and the United Nations Children’s Fund (UNICEF), 2019 (WHO medical device technical series). License: CC BY-NC-SA 3.0 IGO.
2. Frank’s Hospital Workshop. Frank Weithöner, 2022. frankshospitalworkshop.com