I'm assuming you use N2 as a packing MAP gas? Carbon monoxide, to my knowledge is only toxic if inhaled. If present at low levels in MAP gas, I suspect it wouldn't be a health and safety issue for the consumer but the one thing which you might want to check is how it interacts with the food. For example, from my days reading crime novels as a teenager, it causes muscular flesh in people to turn a cherry red colour, this may be desirable from an appearance point of view if packing red meat but if I'm honest I have no idea if carboxyhaemoglobin (which is the chemical which causes it to be red) has any food safety implications or flavour impact?
All in all it's probably worth checking with your gas supplier on what their limits are and what legislation they work to on it, that would be a good starting point then the rest will depend on what you pack I would think.