Gas for labour pain

What is gas and how does it work?

'Gas' refers to forms of breathable, light anaesthetics that can be used for pain relief during the labour and sometimes for giving birth. Gas can also be used occasionally by the woman, for certain medical interventions that may require a level of pain relief.

Nitrous oxide (also known as 'laughing gas') is currently the most commonly used gas for pain relief in labour. It is a colourless, odourless gas, that when diluted (usually by half or 50%) with oxygen, provides a level of pain relief. In higher levels (usually up to 78%) it can be used as part of a general anaesthetic.

Nitrous oxide is the same gas used by dentists for pain relief during dental work. Other types of gases that can occasionally be used in labour (or have been used in the past) are methoxyflurane (or Penthrane) trichloroethylene, enflurane and isoflurane. The latter gases have moved out of vogue because of their perceived side effects. These side effects include increased drowsiness, relaxation of the uterus (increasing bleeding after the birth) and possibly kidney damage for the woman. In Australia it would be unusual to find these other gases being used for pain relief in labour.

Nitrous oxide is absorbed into the woman's blood stream through her lungs and moves rapidly to her brain (within 10 to 15 seconds). Once reaching the brain the nitrous oxide 'depresses' the brain's normal function, changing how the woman perceives her pain. It also has a sedative and at times an amnesic effect. Nitrous oxide is excreted through the woman's lungs as she breathes out. Once she takes the mask away and breathes room air, the nitrous oxide levels rapidly lower with every breath she takes, until none is left in her system after a minute or two.