
I have been asked this question several times so I hope I can answer it well in my blog post today.
There are1500 litres of oxygen in a D cylinder and 3,400 litres of Nitrous Oxide in a D cylinder.
So there is twice as much Nitrous Oxide.
In practical terms most people (but certainly not all) often have nitrous Oxide Sedation at approximately 30% Nitrous Oxide and 70% Oxygen. This is a generalisation which is always a mistake, but with this in mind at 30-40% N₂O and 70-60% oxygen, plus oxygenation at the end of the procedure at 100% Oxygen, this should be no less than 3-5 minutes, you will probably run out of O² before N₂0.
Ideally it is best to keep a spare cylinder of both so you don’t run out at all .The concern of not having both gases is what limits the availability of using Nitrous oxide sedation. By always having a spare it becomes less of a burden and you will tend to use it more, hence benefiting the patient to get their treatment done.