title: Inspiratory work imposed by demand valve ventilator circuits.
abstract: The inspiratory work (WI) imposed by three commonly used demand valve ventilator circuits was studied using a lung model to simulate spontaneous ventilation. The CPU-1 and Engstrom Erica circuits recorded WI of 379 mJ/l and 190 mJ/l respectively. A negative WI of -32 mJ/l was recorded for the Servo 900C, denoting that the circuit performed work on the lung. The demand valves recorded a time delay between inspiratory effort and onset of gas flow, of 300 ms (CPU-1), 190 ms (Servo 900c) and 160 ms (Engstrom Erica). Both the Servo 900C and Engstrom Erica demand valves were able to generate a high inspiratory gas flow response, but the CPU-1 lacked such a flow compensation. Expiratory work was also greatest with the CPU-1 (156 mJ/l) with 141 mJ/l and 90 mJ/l recorded for the Servo 900C and Engstrom Erica. Of the three ventilators studied, the Servo 900C appears to be the ventilator circuit of choice for spontaneous ventilation.
authors.affiliation: Department of Anaesthesia and Intensive Care, Chinese University of Hong Kong, Prince of Wales Hospital, Shatin.
authors.forename: T E
authors.initials: TE
authors.lastname: Oh
authors.forename: E S
authors.initials: ES
authors.lastname: Lin
authors.forename: S
authors.initials: S
authors.lastname: Bhatt
mesh_terms: D006801:Humans; D008168:Lung; D008961:Models, Structural; D012122:Ventilators, Mechanical; D014939:Work of Breathing