Gas is usually available in all delivery suites and most birth centres. It is either attached to the wall of the birthing room, administrated through a machine that pre-mixes the nitrous oxide with oxygen, at adjustable concentration levels, or is wheeled to where the woman is labouring in the room or bathroom, in a portable pre-mixed (50:50) cylinder.
For women planning a homebirth, Nitrous oxide and Oxygen can be hired in pre-mixed cylinders (50:50, called Entonox), usually for the month around the due date of the baby. You will need a letter of authorisation from your local doctor (or GP). Presenting this letter to a medical gas company should enable you to hire your cylinder with a regulator, tubing and mask (and / or mouthpiece).
Some women will hire Entonox 'just in case' they need it for their homebirth, but may or may not use it. Others (especially if they have used gas in a previous labour) will know that this is what they want to use. Discuss this option with your caregiver. Bear in mind that homebirth midwives in England, working as part of the public health system (the NHS), carry cylinders of Entonox with them as part of their standard equipment.
Statistics for the use of gas Australia wide are not published. The NSW Department of health publishes statistics on the use of gas. The rates for 2000 range from about 23.8% to 66.6%, depending on the hospital.
NOTE: Nitrous oxide can separate from the oxygen component of the gas mix inside the gas cylinder at temperatures of less than minus 7oC to minus 8oC. (Not that this is usually much of a problem in Australia!) The danger is that the nitrous oxide can sink to the bottom of the cylinder, meaning that pure nitrous oxide can be inhaled by the woman as a potent general anaesthetic. As a safety precaution, always try and store the cylinder at more than 10oC and lay the cylinder on its side until needed.