Abstract

OBJECTIVE To investigate the mechanisms underlying the improved arterial oxygenation described with flow-limited expiration (FLEX) ventilation in anesthetized horses. ANIMALS 5 healthy adult research horses. METHODS Horses underwent volume-controlled ventilation for 60 minutes (VCV (1) ), followed by 60 minutes of FLEX, and 30 minutes of VCV (VCV (2) ). Main outcomes included the arterial partial pressure of oxygen-to-F io(2) (PF) ratio and electrical impedance tomography (EIT)-derived functional indices at the end of each phase. The EIT data were used to create regional maps of relative lung ventilation and perfusion as well as regional maps of ventilation/perfusion (V/Q) ratios. Ventilation indices derived from EIT included the fraction of expired volume in 1 second (FEV (1) ; %) and the time it took for the EIT signal to drop to 50% of the peak signal at end -inspiration (T- Close 50; seconds). Data were analyzed with 2-way ANOVA for repeated measures. P < .05 was considered significant. RESULTS The PF ratio increased significantly with FLEX compared to both VCV (1) and VCV (2) ( P < .01). There were no differences in the relative distribution of ventilation nor perfusion between ventilation strategies. However, when ventilation and perfusion were superimposed and V/Q ratio maps were constructed, FLEX had a homogenizing effect toward values of 1.0. The FEV (1) was shorter ( P < .01) and the T Close 50 was longer ( P < .001) in all regions during FLEX compared to both VCV (1) and VCV (2) . CLINICAL RELEVANCE Our findings suggest that FLEX ventilation in anesthetized horses enhances regional V/Q matching, likely by pro - longing expiratory aeration and reducing airway closure.