ABSTRACT
The patient exhales and the dead space volume is expelled into the breathing system. The anaesthetist squeezes the bag and fresh gas from the distal tubing is forced into the patient and a variable amount of gas from the reservoir enters the patient. There are three main objectives when using a breathing system: to supply O2 to the patient; to allow removal of CO2 from the system and avoid rebreathing; and to supply anaesthetic gases to the patient. The patient exhales and the dead space volume is expelled into the breathing system, passing down the tubing and fills the reservoir bag again. If the fresh gas flow is too high, the fresh gas flow will fill the bag to a degree and dead space gas will be vented along with alveolar gas. While this avoids rebreathing, it is wasteful and inefficient.
