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)

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.

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