Limited information is available concerning the use of rise time percentage (%) on the SERVO 300 ventilator (Siemens Medical, Danvers, MS)in the VCV mode. We compared various rise time settings during VCV to determine which setting resulted in the lowest TPWOB using a two-compartment mechanical lung model to simulate spontaneous breathing.
WOB was first measured on lung B alone using the Ventrak 1550 (Novametrix Medical Systems, Wallingford CT) at tidal volumes of 200, 400, and 600 mL while peak flow was varied from 40, 60, 80, and 100 L/min with a sine wave flow pattern. Then WOB was measured at these volumes for lung B to drive lung A at normal compliance (0.05 L/cmH2O) and resistance (2.7 cmH2O/L/sec), decreased compliance (0.02 L/cmH20), and increased resistance (17.6 cmH2O/L/sec) while lung A received assistance through an 8.0 endotracheal tube from either VCV of 600 or 800 ml at I:E ratios of 1:3, 1:2, and 1:1, while the rise time % setting was varied from 0 to 10. TPWOB was calculated using the following formula: [TPWOB= WOB(B+A) – WOBB]
A rise time % setting of 0 (1.02±0.46 J/L) resulted in a significantly (p<0.05) lower mean TPWOB compared to a setting of 2 (1.11±0.46 J/L), 5 (1.16±0.43 J/L), 8 (1.17±0.43 J/L), or 10 (1.18±0.42 J/L) across all lung conditions; however, there was no relationship between rise time and TPWOB at high demand flows.
When using VCV and demand flows did not exceed the ventilator’s set flow, a rise time % setting of 0 resulted in the lowest TPWOB.
Rise time % may influence TPWOB during VCV and higher rise time settings may increase WOB in some patients.
D.L. Vines, None.