FIO₂ course when using 1 L/min air in a circle breathing system with an anesthesia machine without active inspired hypoxic guard. If an adult breaths air from a circle breathing system primed with 21% O2, a 1L/min fresh gas flow of air will cause FIO2 to decrease to 12 (twelve) % within 2 min.

FIO₂ course when using 1 L/min air in a circle breathing system with an anesthesia machine with an active inspired hypoxic guard. If an adult breaths air from a circle breathing system primed with 21% O2, a 1L/min fresh gas flow of air will cause FIO2 to decrease below 21%. An active inspired hypoxic guard will reverse this situation. The video starts when FIO2 has already decreased to 21%. Note: the default low FIO2 alarm of 25% has intentionally been lowered to 20% for didactic purpo

FIO₂ course when using 0.7 L/min O₂/N₂O with 29% O₂ in a circle breathing system with an anesthesia machine with an active inspired hypoxic guard. If an adult breaths O2/N2O  from a circle breathing system with a 0.7L/min fresh gas flow with 29% O2, rebreathing will cause FIO2 to decrease below 21%. An active inspired hypoxic guard reverses this situation. The video starts when FIO2 has already decreased to 22%. Note: the default low FIO2 alarm of 25% has intentionally been lowered to 20% for didactic purposes.