We examined the efficiency of an adult circle system with adult bellows to deliver minute ventilation (V(E)) to an infant test lung model. A Narkomed 2B system (North American Drager, Telford, PA) using three modes of ventilator setup were used: A = time-cycled, volume-controlled using bellows excursion to control delivered volume; B = time-cycled, pressure-controlled using inspiratory pressure limit adjustment to control delivered volume; C = time-cycled, pressure-controlled using the inspiratory flow adjustment to control delivered volume. V̇E was measured with two compliances (normal and low) and four endotracheal tube (ETT) sizes (2.5-, 3.0-, 3.5-, and 4.0-mm inner diameter). V̇E was measured at peak inspiratory pressures (PIP) of 20, 30, 40 or 50 cm H2O while respiratory rate (RR) was held constant at 20 breaths/min. V̇E was measured as RR was set at 20, 30, 40, or 50 breaths/min while target PIP was held constant at 20 cm H2O. Data were analyzed using the multiple regression technique. With the low compliance model, V̇E was nearly identical regardless of the ventilator setup. With the normal compliance model, minor differences in V̇E were observed, especially at the highest RR and PIP. V̇E was dependent on RR, PIP, and lung compliance. Overall, the ventilator setup resulted in minor changes in V̇E. Very high PIPs were required to deliver V̇E to the low compliance model. ETT size did not affect V̇E when lung compliance was low; however, smaller ETT size was a factor when test lung compliance was normal, decreasing delivered V̇E at higher PIP and RR. We conclude that with a Narkomed 2B adult circle system V̇E is dependent on PIP, RR, and lung compliance, but not on mode of ventilator setup. Implications: The results of this laboratory investigation indicate that when an adult circle system is used during infant anesthesia, the ventilation delivered depends primarily on the respiratory rate, peak inspiratory pressure, and the compliance of the lung being ventilated, rather than on the specific mode of ventilator setup.
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine