My dad died in front of me

My dad died in front of me

Before he died, he scribbled me a note. They were his last words. I decided not to open it till I was ready. A year later, I opened it and this is what is said, "You are stepping on my oxygen line".

Edit: Holy macaroni with a side of O2, thank you so much for 190 votes!!!

Edit 2: My, my, carbon dioxide, thank you all so much for 370 votes!!!