1995 OPEN FORUM Abstracts
RESPONSE TIMES OF PEDIATRIC/NEONATAL PRESSURE-SUPPORT VENTILATORS
Paul Holbrook, CRTT; Stan Guiles, RRT. Children's Hospital & Health Center, San Diego CA.
Many infants and neonates can only generate very small inspiratory efforts. The object of this study was to evaluate responsiveness of several infant/pediatric ventilators to weak inspiratory efforts at various pressure support (PSV) levels.
Methods: A Newport E100 was used to drive one compartment of a Michigan TTL, set to generate peak inspiratory flowrates of 2LPM (neonatal effort) and 5LPM (pediatric effort) in the dependent compartment. A two-channel recorder allowed simultaneous comparison of pressure changes, which were monitored at the proximal pressure ports of each ventilator's circuit. All ventilators were tested with the same circuits (1 infant, 1 pediatric). Lung model was connected to 2.5, 3.5, 4, and 5 mm ETT. Compliance was set at 1mL/cm H_2O (2.5, 3.5 ETT) and 3mL/cmH_2O (4, 5 ETT). Response time (Tr) was defined as the interval between pressure rise in the drive compartment and the return to baseline from a negative deflection in the dependent compartment. The Siemens SV300, Newport E200, and Bird VIP were tested at PSV levels of 3, 10, 20cm H20 at CPAP of 3cmH20. Sensitivity was maximized in each ventilator while avoiding auto-trigger phenomena.
Results: Aggregate data are presented for each ETT size in milliseconds as mean (SD).
SIEMENS SV300 NEWPORT E200 BIRD VIP
2.5 ETT 84.45 (4.25)49.43 (3.72)147.43 (4.75)
3.5 ETT 87.75 (9.22)63.17 (11.06) 126.77 (1.62)
4.0 ETT 85.39 (13.33) 68.53 (11.32) 138.7(9.86)
5.0 ETT 92.65 (22.81) 85.13 (23.45) 146.48 (8.17)
Various definitions of Tr have been used. Tr as used here was significantly different than other published data (Martin et al ANESTHESIOLOGY 1989;71:977-81 and Nishimura RESP. CARE 1993;38:1253). Including a return to baseline pressure in the definition of Tr, and attachment of a lung model is more indicative of a ventilator's responsiveness to patient efforts. VIP inconsistently triggered breaths during 2.5, 3.5 ETT testing. SV300 performance for 4, 5 ETT was best in 'Adult' mode. Generally the E200 responded more quickly than the SV300 or VIP. CONCLUSION: VIP's discrete sensitivity settings appear to provide a significant limitation to triggering of PSV breaths. Continuously adjustable pressure triggering coupled with proximal pressure monitoring minimizes Tr.