The Impact on Driving Pressure Using the Time Controlled Adaptive Ventilation versus the ARDSnet ARMA Method to Adjust Mechanical Ventilation in Simulated ARDS

Background:ARDS remains a significant problem with high mortality. The only treatments are supportive mechanical ventilation (MV) and proning. However, an unintended ventilator-induced lung injury (VILI) can increase mortality if MV is set inappropriately. Key mechanisms of VILI are overdistension (OD) and repetitive alveolar collapse and expansion (RACE). Conventional MV attempts to minimize OD using a one-size-fits all lower tidal volumes (VT), typically 6 mL/kg IBW. Higher PEEP, adjusted by oxygenation utilizing the ARDSnet PEEP/FIO2 protocol, is used to minimize RACE. Driving pressure (ΔP) reflects characteristics of respiratory system compliance (CRS). It has been shown that high ΔP impacts risk of VILI and ARDS-related mortality independent of VT, PEEP, or plateau pressure (Pplat). We hypothesize that the personalized TCAV method to set and adjust the airway pressure release ventilation (APRV) mode is superior to the one-size-fits-all low VT ARMA method at maintaining a low ΔP with reduced CRS in a test lung. Methods:Two groups were studied using a test lung (ASL 5000) and a Dräger Evita ventilator at the following CRS settings: normal lungs, mild, moderate, and severe ARDS. TCAV group: PHIGH of 30 cm H2O, PLOW of 0 cm H2O, THIGH of 5 s. and TLOW set to achieve the termination of peak expiratory flow (T-PEF) of 75%. ARMA group: used the Volume Control - Assist Control mode with a VT of 400 mL (simulating 6 mL/kg IBW), RR of 12 breaths/min, and inspiratory time of 1 s. PEEP of 5 cm H2O was set for normal CRS, and increased at each level of worsening CRS, consistent with predictable settings for mild (8 cm H2O), moderate (10 cm H2O), and severe (14 cm H2O), ARDS. At each compliance setting, we measured peak inspiratory pressure (PIP), Pplat, and driving ΔP (VT/CRS). Relationships between variables were measured by Pearson r correlation coefficient; groups were compared using a one-tailed unpaired student t-test. Alpha was set at 0.01. Results:ΔP was significantly lower in severe ARDS with TCAV method compared to ARMA method (P = 0.0063). TCAV: as CRS decreased VT decreased (from 680 mL to 372 mL; r = +0.82) and ΔP decreased from 25.4 to 10.5; r = -0.93). ARMA: as CRS decreased ΔP increased (from 7 to 32 cm H2O; r = -0.92) and PIP increased (from 15-46 cm H2O; r = -0.95). Conclusions:The TCAV method is personalized and adaptive to changes in CRS using the slope of the expiratory flow curve and thus will reduce VT in response to a fall in CRS, keeping the ΔP in the safe range.Table 1. TCAV Group NormalLungsMildARDSModerateARDSSevere ARDSΔP10.510.612.725.4PHIGH30303030VT680637551372Table 2. ARMA Group NormalLungsMildARDSModerateARDSSevereARDSΔP7.09.014.032.0PIP15192646VT400400400400