Abstract Rationale Mechanical ventilation is an increasingly common treatment for chronic respiratory failure from a variety of conditions. However, the delivered FiO2 for a given supplemental oxygen flow is not easily determined without an oxygen analyzer. There is limited data on what impact any changes made in ventilatory settings may have on delivered FiO2 from home ventilators. In this study, we sought to determine if delivered FiO2 was affected by changes in commonly used home ventilator modes, pressures, and models. Methods Testing was performed at two different sites (Pittsburgh, PA and Atlanta, GA) on seven different ventilator models: Trilogy EVO, LTV-1250, LTV-1150, VOCSN, Astral, Breas45, and Breas65. Delivered FiO2 was measured with a standard FiO2 sensor (Maxtec r23p01) that was attached to the proximal end of the ventilator circuit, while the distal end of the circuit was connected to an artificial test lung (no human subject testing). With increasing amounts of supplemental oxygen (0-6 liters per minute lpm), FiO2 was measured in seven different ventilator models set to deliver continuous positive airway pressure (CPAP) of 6 cmH2O. These measurements were repeated using synchronized intermittent mandatory ventilation (SIMV) pressure control (PC) 20/6 cmH2O. Finally, the FiO2 measurements were recorded with a positive end-expiratory pressure (PEEP) of 6, 8, or 10 cmH2O while holding the supplemental oxygen flow constant at 2 lpm using a Triology EVO, with repeated measurements using a VOCSN. We conducted all measurements in triplicate and plotted the average of the three measurements. Results In all seven ventilator models, measured FiO2 was positively correlated with supplemental oxygen flow while in CPAP (Panel A) and SIMV PC (Panel B) modes. As supplemental oxygen flow increased, delivered FiO2 increased more rapidly for the LTV models than for the other five ventilator models. At 6 lpm in CPAP, LTVs delivered an average FiO2 0.75, while the other models delivered an average FiO2 of ∼0.45, with similar trends observed in SIMV PC mode. We found that PEEP and measured FiO2 were inversely correlated in most ventilator modes in both the Trilogy EVO (Panel C) and the VOCSN (Panel D). Conclusions As expected, in all ventilator models, supplemental oxygen flow is positively correlated with measured FiO2; however, the correlation appears to be stronger in LTV ventilators compared to other ventilator models. Because delivered FiO2 decreases as ventilator pressures increase, providers should consider re-measuring delivered FiO2 after making pressure changes. This abstract is funded by: NIH
Gaietto et al. (Fri,) studied this question.