Additional information – Entonox

What is Entonox?

Entonox is the trade name for the mixture of 50% Oxygen and 50% Nitrous Oxide, also known as ‘gas and air’. It is a fairly strong pain killer which works very quickly. It is often used to treat pain during childbirth, trauma and wound care. An advantage of this method of pain relief is that it is fully removed by the lungs within a few minutes after you have stopped breathing it. Entonox is safe for use in pregnancy and breast-feeding mothers.

How does Entonox work?

The exact way Entonox works is not fully understood. It is believed that once it is inhaled, Entonox travels to the brain and the spinal cord where it stops the pain from being felt.

Why is Entonox used during endoscopic procedures?

Endoscopic procedures such as flexible sigmoidoscopy and colonoscopy involve the passage of a smooth, flexible tube which has a camera on the tip, into the bowel so that the lining can be inspected. In order that the Endoscopist can view the lining, it is necessary to introduce air into the bowel through the endoscope. This can be uncomfortable and even painful for short periods. Inhaling Entonox can help to make these procedures more manageable. It may be used on its own, or in addition to intravenous (injected) sedation and analgesia if required.

What are the benefits of using Entonox?

Entonox is an effective analgesic (painkiller) which also has sedative and amnesic effects. This means that in addition to relieving pain when used for short periods, it makes the user feel temporarily drowsy, and reduces the memory of the uncomfortable experience.
Entonox puts you in control of your pain relief, because it is self-administered.

Entonox wears off quickly, starting to leave your system as soon as you stop inhaling it. It has very few, mild side effects and leaves the user fit to drive within half an hour after it is last used. This can make Entonox an attractive alternative to injected sedation for those who have commitments such as work or childcare to consider.

Entonox works quickly; you may begin to feel some effect after your first few breaths. It normally takes about two minutes for Entonox to begin to work. After inhaling the gas for a couple of minutes, effective levels of pain relief should be experienced to help you cope with the discomfort of your procedure. The nursing staff will support you in the safe, continued use of Entonox as you require it during your endoscopy.

How is Entonox given?

The Endoscopy nursing staff will show you how to use the Entonox effectively and monitor and support you while you are using it. Before your procedure begins, you will be given a mouthpiece which is attached to a cylinder of Entonox gas. It is important that you hold the mouthpiece firmly between your lips to form a good seal. The nurse will moisten your lips if they are dry to help you do this. You will need to breathe deeply for one to two minutes before there is enough Entonox in your body for it to work. Entonox will only flow when you breathe in, therefore the deeper you breathe, the better your pain relief will be. You do not need to breathe Entonox for your entire procedure; only at times of pain or discomfort.

What are the risks of using Entonox?

Entonox should only be used when prescribed by a healthcare professional. There are minimal risks associated with its short-term use. If it is used repeatedly or continuously for long periods (> six to eight hours) it can affect the user’s blood count, leading to anaemia or vitamin B12 deficiency, or reduce bone marrow function. These problems are very rare and not applicable in this setting.

When Entonox is used for short periods, the main concern is that the gas may become trapped in parts of the body. This is only likely to cause problems for those with specific medical conditions. The nurses will ask you for details of your medical history and carefully assess whether it is safe for you to use Entonox. You should not use Entonox if you have:

  • A recent or current ear infection, or an operation on your ears
  • Recent eye surgery where injections of gas have been used
  • Recently been scuba diving (within 48 hours) or have decompression sickness
  • A collapsed lung or pneumothorax
  • Lung disease or breathing difficulties (unstable asthma, emphysema)
  • A head injury (or suspected or known increased pressure on the brain)
  • A known problem with air trapped in the body (e.g., in an artery)
  • A severely bloated stomach
  • Injuries to the face and jaw
  • Paraquat poisoning (a weedkiller)

What are the side-effects of using Entonox?

Entonox can make you feel dizzy or nauseous (sickly) but these side-effects usually settle if you slow your breathing down or stop using the gas. Some people complain of parasthesia (a tingling sensation) and light-headedness while using the gas

If you keep breathing Entonox continuously, you will eventually become drowsy and unable to hold the mouthguard to your lips. The nursing staff supervising you will give you some oxygen while the effects wear off, and you will wake up naturally as this happens.

Use of Entonox will also be discontinued if you start to complain of earache, if you find the side-effects unpleasant or persistent, or if you are not finding it helpful, in which case alternative pain-relieving medication may be used.

Are there any restrictions after using Entonox?

You will be monitored for half an hour after you have stopped using Entonox, until the nursing staff are happy that you have recovered and are safe to be on your own and resume your normal activities, such as driving and working.