Entonox (gas and air) in the endoscopy unit

Entonox is a mixture of a gas called nitrous oxide and oxygen. It is also called gas and air.

You can breathe in Entonox to control pain and anxiety during some medical tests and procedures. This is a simple way to help with pain and anxiety. It is quick to work and the effect wears off in minutes. You do not lose consciousness.

You breathe in the gas mixture through a mouthpiece and can control how much pain relief you have.

Entonox is often used to treat pain during childbirth. The ambulance service and hospitals also use it for different procedures and conditions. In the endoscopy unit, we might offer you Entonox to help with pain during some bowel tests.

Who can use Entonox

Before your procedure, we record your blood pressure, pulse and the amount of oxygen in your blood using a special machine. We also ask some questions to make sure that Entonox is suitable for you.

Please tell us if you:

  • have recently used Entonox for a procedure
  • currently have, or recently had, an ear infection
  • recently had an operation on your ears
  • recently had eye surgery
  • recently had a head injury, which meant that you had to go to hospital
  • have recently been scuba diving
  • are pregnant or think that you might be pregnant
  • recently had a condition that caused sudden or severe breathing problems, such as a chest injury or a collapsed lung
  • have emphysema (a lung condition) or long-term breathing problems, such as bronchitis or asthma
  • have been told that your level of vitamin B12 is low

In these cases, Entonox should not be used.

How to use Entonox

If Entonox is suitable for you, we show you how to use it. 

We explain how to hold the mouthpiece firmly in place to make a good seal. 

We then ask you to breathe deeply for 1 to 2 minutes. This allows us to check that you feel the effects of Entonox before we start the procedure.

Entonox flows when you breathe in. The deeper you breathe, the better Entonox can help your pain.

Side effects of Entonox

Entonox is generally very safe, but there are a few possible side effects.

  • You might feel dizzy or drowsy (sleepy). If you become very sleepy, you might drop the mouthpiece. This prevents you from breathing in too much gas. When you start breathing in normal air, you wake up again. It is important that only you hold the mouthpiece.
  • Entonox might make you feel sick (nausea).
  • Breathing in the gas can make you light-headed and give you a tingly feeling (usually in your fingers).

To reduce these side effects, breathe slowly and calmly when you use Entonox. The side effects quickly improve when you stop breathing in the gas.

If you use Entonox for longer than 6 to 8 hours, this might cause:

  • anaemia (when you do not have enough healthy red blood cells to carry oxygen to your body's tissues)
  • a lack of vitamins in the body
  • bone marrow that does not work well (this is the soft tissue inside bones that makes new blood cells)

These side effects are very rare. Procedures like a flexible sigmoidoscopy and colonoscopy (tests to check inside your bowels) only last for about 30 minutes. 

Other options to Entonox

If Entonox is not suitable for you, we can talk about other options to control your pain.

Intravenous sedation is when we give you pain medicine through a small plastic tube called a cannula into a vein. You have a mixture of a painkiller and sedative. This makes you feel sleepy and relaxed.

Risks of using Entonox

There are very few risks to using Entonox for pain relief.

Entonox is not always suitable for people with some respiratory (breathing) conditions because the gas may get trapped in the body. We assess you before we decide to give you Entonox. 

Leaving hospital

As the effects of Entonox wear off quickly, you can leave hospital when you feel ready. 

For your safety, we recommend that a responsible adult takes you home. We also recommend that you do not drive until you have fully rested.

Resource number: 3874/VER3
Published date: June 2022
Review date: June 2025

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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