Home after 15 days in hospital when 02 dropped to 77. On 5 l now which means tanks. How do you know how may to take with you? Think about getting caught out and not having enough. Prayerfully I will continue to get better, and go back to 2 l. Also I seem to be focusing a lot on my breathing so I can control when it starts to decline down walking. I don’t understand the pursed breathing, maybe I am just focusing too much on breathing. Does any know if they make a portable at 5l