A COMPARISON OF 3 MODES OF VENTILATION WITH THE USE OF AN ADULT CIRCLE SYSTEM IN AN INFANT LUNG MODEL

We examined the efficiency of an adult circle system with adult bellow s to deliver minute ventilation ((V) over dot E) to an infant test lun g model. A Narkomed 2B system (North American Drager, Telford, PA) usi ng three modes of ventilator setup were used: A = time-cycled, volume- controlled using bellows excursion to control delivered volume; B = ti me-cycled, pressure-controlled using inspiratory pressure limit adjust ment to control delivered volume; C = time-cycled, pressure-controlled using the inspiratory flow adjustment to control delivered volume. (V ) over dot E was measured with two compliances (normal and low) and fo ur endotracheal tube (ETT) sizes (2.5-, 3.0-, 3.5-, and 4.0-mm inner d iameter). (V) over dot E was measured at peak inspiratory pressures (P IP) of 20, 30, 40 or 50 cm H2O while respiratory rate (RR) was held co nstant at 20 breaths/min. (V) over dot E was measured as RR was set at 20, 30, 40, or 50 breaths/min while target PLP was held constant at 2 0 cm H2O. Data were analyzed using the multiple regression technique. With the low compliance model, (V) over dot E was nearly identical reg ardless of the ventilator setup. With the normal compliance model, min or differences in (V) over dot E were observed, especially at the high est RR and PIP. (V) over dot E was dependent on RR, PIP, and lung comp liance. Overall, the ventilator setup resulted in minor changes in (V) over dot E. Very high PIPs were required to deliver (V) over dot E to the low compliance model. ETT size did not affect (V) over dot E when lung compliance was low; however, smaller ETT size was a factor when test lung compliance was normal, decreasing delivered (V) over dot E a t higher PIP and RR. We conclude that with a Narkomed 2B adult circle system (V) over dot E is dependent on PIP, RR, and lung compliance, bu t not on mode of ventilator setup. Implications: The results of this l aboratory investigation indicate that when an adult circle system is u sed during infant anesthesia, the ventilation delivered depends primar ily on the respiratory rate, peak inspiratory pressure, and the compli ance of the lung being ventilated, rather than on the specific mode of ventilator setup.