A Comparison of Two Ventilators Using Volume Guarantee Modes for Ventilation of the Neonate Using a Lung Model

Background: Volume guarantee modes (VG) are used with increasing frequency for the neonatal population in an attempt to minimize lung injury and hypocarbia due to unintentional hyperventilation. Ventilator manufacturers utilize different proximal flow sensor technology and software to achieve VG, and investigation of the behavior of each ventilator is useful. This ex vivo experimental design evaluated the Vti, Vte, and PIP delivered during VG modes with the Vyasis Avea (Avea) and Drager VN500 Babylog (VN500) using the IngMar Medical ASL 5000 electronic lung simulator (ASL 5000). Methods: The ASL 5000 was programmed to model a 1-3 kg body weight neonate with normal to moderately affected lungs. ASL 5000 settings: Cst 1.5 mL/cm H2O, Raw 70 cm H2O/L/s, Pmus 0 cm H2O (passive), f zero. The EST on the Avea, and circuit check on the VN500, were completed prior to testing; the proximal flow sensors were zeroed on each ventilator. Trials were conducted at ambient temperature and humidity. Constant settings on the Avea: 30 breaths/min, PEEP 6 cm H2O, flow trigger 0.5 L/min, FIO2 0.21, Rise 5. Constant settings on the VN500: 30 breaths/min, PEEP 6 cm H2O, FIO2 0.21, slope 0.20 seconds, Pmax 50 cm H2O. Variable settings on each ventilator were: inspiratory time 0.25, 0.30 and 0.35 seconds and tidal volume to simulate an 800 g, 1 kg, 2 kg and 3 kg infant at 5 mL/kg (4, 5, 10 and 15 mL). Each ventilator was tested with each variable setting for a total of two minutes using the ASL 5000. After a stabilization period of 15 breaths, delivered Vti, Vte, and PIP were recorded continuously by the ASL 5000. The results for each parameter were then averaged over a 1-min period, and the standard deviation was calculated for each measurement. Results: The Avea and VN500 delivered similar volumes and pressures as recorded by the ASL 5000 with less than ± 0.02 standard deviation for each parameter. The Avea demonstrated wider standard deviation due to periodic spikes in Vti and PIP. The VN500 consistently delivered lower tidal volumes as measured by the ASL 5000 compared to the Avea, usually at lower measured PIP. This delta varied with each breath. Conclusions: The VN500 and Avea deliver consistent Vti, Vte, and PIP in a passive model. Measured values higher than set VG on both ventilators, and lower Vti and Vte on the VN500, may be due to variances in how each ventilator deals with the compressible volume of the breathing circuit and temperature and saturation of the inspired gas.