I've heard women say it before and I remember thinking it myself in labour......the breathing techniques are working brilliantly but I'd love a bit of gas & air.....how on earth do I combine the two? Breathing techniques for labour often encourage breathing in through the nose; to warm, moisten and cleanse the air (as well as slowing the breath), and out through the mouth. Gas & air use requires mouth breathing.
You don't have to breathe in through the nose and out through the mouth for labour breathing to be effective, particularly if you have nasal congestion (which can occur at the end of pregnancy) or nasal polyps. However, many women do find the regular rhythm of 'in through the nose/out through the mouth' helpful. This can cause some confusion when trying to combine it with using gas & air (entonox). One Mum told me that she used some choice language about me in labour when she found herself temporarily confused by this very issue! Apparently she forgave me after working out a method that worked for her :).
Most women will be offered a mouth piece to use for gas & air. They put their lips around the flat, white tube, making an air tight seal, and breathe deeply in through their mouth to receive the gas & air. So to combine labour breathing with gas & air, simply use mouth breathing. Another mother told me that she just breathed out into the tube as well and it made a low 'moo-ing' sound that she found very comforting; that sound became her focus and worked a treat for her! Mamas are amazing warrior women who freestyle in labour and find their own best way.
But! Back to the topic: Gas & air has a short lag before it works, of about 30 seconds, and is out of the woman's system within a couple of minutes; so women have found it helpful to take 3 or 4 deep lung fulls of the gas & air right at the start of a contraction and then just use their usual labour breathing to breathe through the rest of the contraction. Strong contractions in established labour last 60 - 90 seconds on average; hence just breathing the gas & air through the first 30 seconds should give a good level of pain management through the remainder of the contraction. As gas & air is out of a mother's system so fast, this method should mean the mother feels alert during the gap between contractions; ensuring she's ready to sense the next contraction coming in and can take the gas & air as soon as it starts.
I like this article for an overview of the pros and cons of gas and air, plus a nice pic of the mouth piece! https://www.motherandbaby.co.uk/pregnancy-and-birth/birth/getting-ready-for-birth/natural-pain-relief-is-gas-and-air-your-best-option-in-labour