ABSTRACT
A low-flow system refers to a single breathing system in which the fresh gas flow is 3L/min or less. There are only two low-flow breathing systems: the Waters to-and-fro system and the circle system.
The Waters system The Waters system consists of an expiratory valve T-piece for fresh gas, sodalime canister and reservoir bag connected in series. Although widely used in the past, numerous advances have led to its virtual abandonment. The apparatus is bulky and needs to be placed close to the patient’s head, causing traction on the endotracheal tube or facemask and so restricting surgical access. There is progressive increase in dead-space as soda-lime nearest to the patient is exhausted. Settlement of soda-lime granules may lead to the formation of a channel between the uppermost part of the soda-lime and the well of the canister through which gas can pass without removal of carbon dioxide. There is furthermore a risk of soda-lime dust inhalation as a consequence of the proximity of the canister to the patient’s airway.
