The impact of adaptive flow volume control on lung-protective ventilation

SESSION TITLE: Outcomes of Mechanical Ventilation in the ICU SESSION TYPE: Rapid Fire Original Inv PRESENTED ON: 10/10/2023 12:55 pm - 01:40 pm PURPOSE: Adaptive flow (AF) is a patient-comfort feature used in the volume control mode on some mechanical ventilators. When activated, AF allows for increased flow in response to detection of excessive patient demand, which is sensed by the decreased airway pressure in the circuit. Since flow is increased over a fixed inspiratory time, larger tidal volumes (Vts) may be delivered than the desired setting. This study sought to assess the impact of AF on the ability to achieve target Vt < 8 mL/kg. Here we present a preliminary analysis of that data. METHODS: We conducted a retrospective cohort study of medical intensive care unit patients receiving volume-targeted mechanical ventilation for at least 48 hours in the year before (2017-2018) and the year after (2018-2019) system-wide implementation of a ventilator featuring AF. The primary outcome was the proportion of patients receiving an average Vt > 8 mL/kg of ideal body weight (IBW) during the first 48 hours of intubation. Secondary outcomes included the median exhaled Vt, the median difference between set and exhaled Vt, new incidence of acute respiratory distress syndrome (ARDS), need for refractory hypoxemia interventions, ICU and hospital mortality, ICU and hospital length-of-stay, and ventilator-free days. RESULTS: Of 2680 charts pulled, to date we have screened 1482 and included 235 patients, 131 in the control group and 104 in the AF group. At baseline, patients in the control group were more likely to have asthma, COPD, ARDS on presentation, and had higher sequential organ failure assessment scores. Despite no difference in set tidal volume between groups, patients in the AF group were more likely to receive an average Vt > 8 mL/kg (13.7% vs 6.4%; odds ratio 3.4, 95% confidence interval 1.7 - 6.7; p = 0.0003). The median IBW-adjusted Vt was 6.6 mL/kg (interquartile range (IQR) 6.3 - 7.2) and 7.2 mL/kg (IQR 6.8 - 8.3) for the control and AF groups respectively (p < 0.0001). The median difference between set and delivered Vt was +27.7 mL (or +0.44 mL/kg) in the control group and +59.6 mL (or +0.97 mL/kg) in the AF group (p < 0.0001). These differences remained significant after adjusting for baseline characteristics. Of the secondary outcomes evaluated, new incidence of ARDS, use of neuromuscular blockade, and use of inhaled pulmonary vasodilators were all higher in the control group, but none remained significant after adjustment for covariates on multivariate logistic regression. CONCLUSIONS: This small preliminary analysis of a large retrospective study shows that volume control ventilation featuring AF is associated with delivery of average Vts higher than is recommended for lung protective ventilation. To assess the impact on patient-oriented outcomes will require ongoing data collection and analysis. CLINICAL IMPLICATIONS: AF may improve patient comfort at the expense of using improper lung protective ventilation. A larger sample size will be needed to evaluate whether this translates into increased risk of ventilator-induced lung injury, particularly for patients with ARDS. DISCLOSURES: No relevant relationships by Matthew Barraza No relevant relationships by Alex Carter No relevant relationships by Robert Easterling No relevant relationships by Gregory Eisinger No relevant relationships by Zacharia Grami No relevant relationships by Jonathan Henricks No relevant relationships by Derrick Herman No relevant relationships by Quinn Hosler No relevant relationships by Aubrey Husak No relevant relationships by Meghana Moodabagil