Rather, by allowing a steady flow of the inert gas into the bag, there will be no oxygen from the start. The flow of the inert gas into the bag also flushes away any exhaled carbon dioxide. As there is no build-up of carbon dioxide, there is no panic reaction.
Note: To recap, there is nothing special about the inert gas used in terms of whether it is Nitrogen, Helium or Argon. Indeed, any gas that does not react with the body and that is odorless and available in a compressed form, would be suitable. Most often the choice is determined by what is available.
Most compressed gases are only available in high pressure cylinders which are leased from commercial gas supply companies (such as BOC, Linde or Air Liquide). The drawback with accessing a compressed gas in this way is the paper trail that it generates. There is no anonymity. An additional deterrent is that the commercial compressed gas cylinders are often large, heavy and difficult to transport. Suspicion might arise if an elderly or very sick person is seen leasing a cylinder from their local gas outlet. There is an added complication in that if a friend were to collect the cylinder for them, this other person may become legally implicated in assisting in the suicide. These issues are disincentives to using a commercial supplier to lease a high-pressure, compressed inert gas cylinder.
Take-home cylinders of Nitrogen, Helium and Argon can often be purchased online and can be used effectively with the Exit Bag. It is the availability of inert gases in easy-to-acquire, purchase-outright, take-home cylinders that has led to renewed interest in the Exit Bag method.