Volume Guaranty (VG) Mode Reduces The Percentage of Too High or Too Low Tidal Volume (VT) During Conventional Mechanical Ventilation in Neonates 1735

Abstract

Our hypothesis was that control of VT must have limited too high VT(overinflation) and too low VT (ineffective ventilation). During pressure controlled (PC) mode, VT is not controlled. During VG mode, now available, VT measured at the level of the Y piece, is controlled by adaptation of the positive inspiratory pressure (PIP) to deliver a target VT. The aim of this study was to compare VT and PIP during PC and VG modes. VT and PPI were measured over one three-hour period during each mode, at a rate of 1/10 sec. Five newborn infants (GA 29.8 ± 4.4 w, BW 1590 ± 680 g, PNA 14± 8 days) were studied with Babylog 8000plus et 5 newborn infants (GA 32.3 ± 6.5 weeks, weight 1940 ± 1270g, postnatal age 9.7± 9.4 days) with Evita 4 neoflow. The ventilator setting was performed to maintain TcPO2 and TcPCO2 at a predefined level. Each newborn was studied twice. We thus compared 10 paired 3-hour periods in PC mode and VG mode using the Wilcoxon Signed-Rank test. Variability was defined by the following formula: 100* SD/mean and was expressed in percent. The results are expressed as the mean (SD) in PC vs VG mode. With Babylog: PIP mean did not differ 19.2(2.5) vs 19.7(2.5) mbar (NS). Variability in PIP increased during VG, 6.4(3.6) vs 24.4 (8.5)% (p<0.01). VT was respectively 5.6 (2.2) vs 5.0 (2.3) ml/kg (p=0.05). Variability in VT decreased during VG mode from 18.7(4.9) to 11.9(4.4)% (p<0.01). The percent of very high VT (above 1.2 * mean VT) or very low VT (under 0.8* mean VT) decreased from 24.0 (10.2) to 6.6 (5.0)%,(p<0.01). Respiratory rate, minute ventilation and FiO2 did not differ. With Evita 4: PIP did not differ: 24.9 (5.8) vs 25.9 (6.0) mbar (NS). Variability in PIP increased VG mode from 8.0 (4.4) to 19.4 (5.3)%(p<0.01). VT did not differ 6.3 (2.1) vs 6.6 (2.0) ml/kg (NS). Variability of VT was 16.2 (7.3) vs 11.8 (7.2)% (p=0.06). The number of very high or low VT decreased during VG mode from 25.0 (18.2) to 5.6 (6.6)%, (p=0.01). Respiratory rate, minute ventilation and FiO2 did not differ significantly Thus, in this studied population, the variability of VT was high during PC mode. During VG mode, the variability of VT decreased, and the number of very high or very low VT was reduced four-fold but with a large increase in PIP variability.